From hbr@mailman.qth.net  Mon Nov  3 12:37:53 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Mon, 3 Nov 2003 07:37:53 -0500
Subject: [HBR] Homebrew 1929 Superheterodyne Receiver: UPDATE
Message-ID: <003c01c3a207$4e87cfa0$c7d549c6@greg>

Well, the receiver metal work is ALL DONE---the receiver paint work is ALL
DONE....(at last!)...and this past weekend I wired the filaments & the
primary AC wiring...

I'm on night shift for the next two weeks, & I'm quite confident that I can
get everything completed by the middle of the month: that'll leave me a good
two weeks to get the thing (hopefully!) trouble-shot & operational, well in
advance of the Bruce Kelley 1929 QSO Party...

Boy, a project of this magnitude sure does take time...! Thus far, I figure
I put in AT LEAST a GOOD WEEK drawing the schematic/laying out the parts (on
paper) & planning the thing, TWO weeks doing all the metal work (drilling
holes for sockets, screws, transformers, tie bars, AD NAUSEUM!), and ANOTHER
good week doing the priming/painting---a WHOLE MONTH, & the darned thing is
only now getting its first whiffs of rosen & solder...

I must say, though, thus far, it's a pretty-looking thing: those white
National & Millen ceramic sockets sure are FB nestled-in atop the flat black
painted chassis top...

A good supply of 224's/224A's has been steadily arriving at the door, c/o
eBay...

I can hardly wait to hear those push-pull 245's swing into action! Hopefully
this monster will PLAY as good as it LOOKS! Hi Hi.

Will keep you posted...

~73!~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Mon Nov  3 13:58:14 2003
From: hbr@mailman.qth.net (Brett Gazdzinski)
Date: Mon, 03 Nov 2003 08:58:14 -0500
Subject: [HBR] RE: [AMRadio] Homebrew 1929 Superheterodyne Receiver: UPDATE
In-Reply-To: <003c01c3a207$4e87cfa0$c7d549c6@greg>
Message-ID: <00a001c3a212$8740d570$adb220a6@wcomnet.com>

Eddy,
What are you building?

Yes, my designs take about a month of looking in every book and
at every receiver diagram I have, another month or more going through
all the parts I have to get nice ones that will work well, another month
laying out parts, moving things around, changing the odd bit,
then moving things around again.

The holes, once things are finalized are quite quick, I did them all
over the weekend, the chassis and the front panel.

Painting and labeling the controls is always a giant pain in the butt.

Brett
N2DTS



> -----Original Message-----
> From: amradio-admin@mailman.qth.net
> [mailto:amradio-admin@mailman.qth.net]On Behalf Of Eddy Swynar
> Sent: Monday, November 03, 2003 7:38 AM
> To: Amradio@mailman.qth.net; hbr@mailman.qth.net;
> antiquewirelessassociation@egroups.com
> Subject: [AMRadio] Homebrew 1929 Superheterodyne Receiver: UPDATE
> 
> 
> Well, the receiver metal work is ALL DONE---the receiver 
> paint work is ALL
> DONE....(at last!)...and this past weekend I wired the filaments & the
> primary AC wiring...
> 
> I'm on night shift for the next two weeks, & I'm quite 
> confident that I can
> get everything completed by the middle of the month: that'll 
> leave me a good
> two weeks to get the thing (hopefully!) trouble-shot & 
> operational, well in
> advance of the Bruce Kelley 1929 QSO Party...
> 
> Boy, a project of this magnitude sure does take time...! Thus 
> far, I figure
> I put in AT LEAST a GOOD WEEK drawing the schematic/laying 
> out the parts (on
> paper) & planning the thing, TWO weeks doing all the metal 
> work (drilling
> holes for sockets, screws, transformers, tie bars, AD 
> NAUSEUM!), and ANOTHER
> good week doing the priming/painting---a WHOLE MONTH, & the 
> darned thing is
> only now getting its first whiffs of rosen & solder...
> 
> I must say, though, thus far, it's a pretty-looking thing: those white
> National & Millen ceramic sockets sure are FB nestled-in atop 
> the flat black
> painted chassis top...
> 
> A good supply of 224's/224A's has been steadily arriving at 
> the door, c/o
> eBay...
> 
> I can hardly wait to hear those push-pull 245's swing into 
> action! Hopefully
> this monster will PLAY as good as it LOOKS! Hi Hi.
> 
> Will keep you posted...
> 
> ~73!~ Eddy VE3CUI - VE3XZ
> 
> _______________________________________________
> AMRadio mailing list
> AMRadio@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio

From hbr@mailman.qth.net  Wed Nov  5 01:25:39 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Tue, 4 Nov 2003 20:25:39 EST
Subject: [HBR] Re: HBR digest, Vol 4 #115 - 2 msgs
Message-ID: <104.38c0c4f7.2cd9ab93@aol.com>

And to think I was contemplating mass production of an HBR like the ones 
their building on
   here.  Keep up the good work.  Not enough home brewers left.  kc5fmx


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From hbr@mailman.qth.net  Sun Nov  9 02:57:38 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Sat, 8 Nov 2003 21:57:38 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 1B
Message-ID: <3FAD66D2.9625.26FC2A8@localhost>

The excitement -- is that the right word? -- continues ...

The first big question is whether I can build a sufficiently linearly 
tuning oscillator to justify a dial calibrated directly to 10 cps 
increments.   That's especially a dicey issue with a tuning cap of 
unknown characteristics -- but this cap (which rotates 240 degrees to 
cover its range) is the only thing I've got that will allow tuning 180 
degrees without end effects.   And it is of outstanding quality so if it 
can be linearized, it'll be good.

I've got the oscillator mechanicals roughed out.   The posts on the 
right side of the dial mechanism formerly supported the stator of the 
built-on tuning cap; now they will hold the large face of a 3x4x5 box 
in which the new tuning cap and other oscillator parts will live.   To 
save space, I shortened the posts about 5/8".   That turned out to be 
more interesting than expected because the posts are surface 
hardened -- anyone know what process gives a silver color?   Seems 
like overkill to me ... what sort of wear would such posts experience? 

The trickiest part was having to drill and tap 5/8" deeper in the cut-off 
end.   Three of them were no problem; the fourth somehow was 
surface hardened in the bottom of the hole -- a crystal or two of 
whatever was used (cyanide?) must have gotten down there.   And I 
had to Dremel a notch at the right point on each post before I could 
cut them off with a hacksaw.   

Lengths had to be exactly the same: I cut the posts a hair long, then 
drilled through a block of wood (of proper thickness) and used a belt 
sander to grind the ends off flush.  

The assembly went together without problems -- as Jim has noted it 
takes some time to drill and tap a bunch of holes, but I had only 24 
of them (3-48 and 4-40) so it wasn't that bad.

Tapping holes in an aluminum chassis or box usually isn't too 
successful because the material is too thin and the usual chassis is 
dead soft.   The following trick makes it work for 3-48 machine 
screws (a la command sets):  Drill a tiny hole -- say #50 or a bit 
smaller. If you're attaching a cover, drill through both pieces.  By 
using a Dremmel while spinning the bit in an electric drill, taper the 
butt end of the correct drill to tap for the screw you want -- #39 for 3-
48 -- to a sharp point.   Chuck with tapered end out in drillpress (or 
electric hand drill), lube with silicone grease, and quickly force (while 
spinning) through your pilot hole.   You now have a hole of the correct 
tapping diameter but in metal 2x to 3x the thickness of the rest of the 
sheet -- of course you do not remove the upset material!   This area 
has also been work hardened, so the thread will be much stronger 
than in unworked metal of the same thickness.   Holes can be 
tapped in the usual way -- I usually chuck the tap in a variable speed 
reversing hand drill but one of the old hand crank drills also works 
well.   The hole in the cover plate should be enlarged to fit over the 
upset; a #31 drill works for 3-48 screws.   

Try this on scrap first -- practice makes perfect!

It's more work than sheetmetal screws, but it goes quickly and gives 
a strong and good looking result on the usual 0.050 chassis.   Also, 
you can remove and replace the machine screws many times, if 
necessary.   This sort of thing may be unnecessary for a simple box 
cover, but for an oscillator assembly you get close to the stiffness of 
a cast box with the ease of working of sheet metal and a fraction the 
weight.

I needed mainly the stiffness (with minimum weight) because the 
entire oscillator -- box, tuning cap, sockets, tubes, small parts, and 
some wiring -- is supported on the four posts of the LM worm gear 
drive.   Looking down, the assembly is basically a backwards 'L' 
supported only at the short end of the bottom -- the cast gear frame.  
 I may eventually add a single support at the top (rear) of the 'L', but 
since it will go to the center of an aluminum chassis, a high 
stiffness/weight ratio is still a good idea.

Pictures -- does anyone recognize that tuning cap?   The box doesn't 
actually touch the panel, tho it is a bit closer than I wanted.   Looking 
at the 'C' photo (oscillator box open) the coil mounts by one end on 
the larger upper hole of the two in the space between the cap and the 
tube sockets.   It's a plastic (plexglas) tube about 3/4" dia x 2-1/2" 
long that held craft 'glitter' -- available at Wal-Mart and doubtless 
many other places.

http://www.collie-rescuers.com/ebay/11803A.jpg
http://www.collie-rescuers.com/ebay/11803B.jpg
http://www.collie-rescuers.com/ebay/11803C.jpg

I spent several hours researching tubes.   Because they were never 
cheap (and transistors were starting to come on the market), most 
subminiature tubes were used only by the military.    There are at 
least four battery filament triodes but all have 100 ma (or more) 
filaments and some are rated only for push-to-talk service -- 100 hour 
filament life.   There probably was a triode designed for hearing aid 
service (remember the cigarette pack size hearing aids?) but I don't 
have a suitable index of tube types to numbers; I have to start with a 
type number and retrieve characteristics.  

I did discover a whole line of subminiature tubes (roughly 5904... 
5908) designed for 26.5 volts on filament *and plate.*    I know of no 
military equipment that used such tubes -- does anyone?   'Far as I 
knew, the 26.5 volt plate era began and ended with the R-392 -- 
miniature tubes in that one.

I considered acorn tubes but the sockets are large and the only tube 
I could find is the 958 which has a 100 mA filament.

I was unable to locate even one miniature battery operated single 
triode.   The 3A5 is a dual triode, but has a 100 mA filament.   It 
looks like the best bet is triode connected 1U4's (minature, 1.4 volt 
0.05 amp filament, sharp cutoff pentode) and I'll try those first.  There 
are various stability questions with these tubes but for the more the 
more than 10-fold reduction in total heat production, it's worth a shot. 
Worst comes to worst I can replace with 6AF4's.

An invaluable resource for researching tubes is:

http://home.wxs.nl/~frank.philipse/frank/frank.html  

*19,000* tube types are indexed there, complete with data sheets. I 
found a few oddballs that were missing but I'll bet they'll be there in a 
few months -- the site owner does regular updates and posts 
requests for help on unknown types.

The oscillator box will be warmed by the other tubes in the set but 
that'll be only via the air, so it will happen very slowly.   Since the box 
is closed, all the parts affecting the frequency will warm up at the 
same rate, meaning that temperature compensation should be 
simple.   In fact I'll use a plastic form for the oscillator coil: If properly 
designed (a bit of space between the turns) such coils are self-
compensating and can even have a negative temp coefficient so they 
compensate for the positive coefficient of the other parts.

(The miniductor local osc. coils you see in some HBR projects are a 
really bad idea -- the wire is often not firmly gripped in the support 
bars and as the coil gradually warms, it will from time to time jump to 
a new position ... I only tried that once!

One must of course watch out for self-heating of oscillator tank parts 
due to circulating RF currents.   That means heavier wire than you'd 
expect for the coil and using multiple smaller NP0 caps in parallel for 
the necessary shunt cap.   Also the oscillator power level must be 
kept low.

Since I'm not using the FT-101 capacitor, there's no clear advantage 
to using the FT-101 tuning range.   I'll try tuning the oscillator 5.2-5.7 
Mcs instead of 8.7-9.2 Mcs.   That should be easier to linearize and 
definitely will help stability.   I haven't yet done the spur checks for 
that, (I will before winding any coils!) but it ought to be okay.  

('Ought to be okay' ... Hehehe ... ) 

This oscillator and dial mechanism is *big* -- several times that of the 
FT-101 and maybe double that of the 1MHBR -- but if the 
performance the individual parts are capable of can be realized in the 
assembly, it'll be well worth the extra space.   And it's all above 
chassis, so the space below is available for other circuits provided 
they do not generate much heat. 

I've made up the plate transformer -- two Radio Schlock 120 to 6.3-0-
6.3 x 3A filament transformers donated their primaries to make a 
single 120 to 120 transformer. They are bobbin-wound so you 
disassemble, unwind each secondary, cut off that end of the bobbin, 
use a sander to grind the center partitions to half thickness, restack 
the laminations inside the paired primaries, and reassemble.   Now I 
just have to wire up the power supply in the junk chassis, wire the 
oscillator and go from there.

Not being able to find suitable scrap, I ordered the front panel plate 
today.   About $29 for two 8" x 14" x 0.125" plates, half of that is 
shipping from WA via UPS.   Expensive I suppose, but their service 
is outstanding and the site works beautifully:

www.onlinemetals.com

Naw, I don't get anything by recommending them -- I could get a 5% 
discount, if everything worked right and I ordered again within 30 
days but I'm afraid I can't afford to save that much money.   

If I can get linear tuning then the next step is to wire up the Hahnel 
oscillator (multiples of 1.75 Mcs) and premixer and get that stuff 
working.   Then start over with the real receiver ... probably a couple 
months down the road, at least.

Walt
KJ4KV  

From hbr@mailman.qth.net  Wed Nov 12 12:09:56 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Wed, 12 Nov 2003 07:09:56 -0500
Subject: [HBR] Items For SWAP...
Message-ID: <004401c3a917$4e7a84a0$dbd549c6@greg>

Greetings All,

I came up two items short here in my 1929 homebrew replica superheterodyne
receiver project, specifically, two ceramic plate caps for my 224 globe
tubes...

Does anyone have a pair they'd like to part with...? They can be either
National Radio type, or James Millen---as long as they're both white, glazed
ceramic & presentable, I don't care.

I'd be willing to trade TWO of my National 813-sized ceramic plate caps
(i.e. R.F.E.---"Removed From Equipment") for your two 807/224-sized ceramic
plate caps.

Anything out there...?

BTW, the behemoth is done---but NOT working (naturally!). The audio stages
are FB, but little else. NOW comes the learning process...! I'm working
backward from the detector stage on up to see what gives.

It is one HEAVY mutha'! Good lookin', too, in a roaring 20's kind of way.
Sure does look like it's hiding a lot of potential from me...with any luck,
I'll be able to unlock its secrets BEFORE the 1929 QSO Party...!

May have some digital pix taken & available on the weekend, too, in case
anyone is interested---but I HATE taking shots of non-working gear...

Thanks & my very

~73~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Wed Nov 12 13:01:32 2003
From: hbr@mailman.qth.net (Tom Smith)
Date: Wed, 12 Nov 2003 07:01:32 -0600
Subject: [HBR] Items For SWAP...
In-Reply-To: <004401c3a917$4e7a84a0$dbd549c6@greg>
Message-ID: <web-71191252@mail.hal-pc.org>

Hi Eddy,

I think I have a pair if still needed.

Tom  N5AMA

On Wed, 12 Nov 2003 07:09:56 -0500
  "Eddy Swynar" <gswynar@durham.net> wrote:
>Greetings All,
>
>I came up two items short here in my 1929 homebrew replica 
>superheterodyne
>receiver project, specifically, two ceramic plate caps for my 224 
>globe
>tubes...
>
>Does anyone have a pair they'd like to part with...? They can be 
>either
>National Radio type, or James Millen---as long as they're both white, 
>glazed
>ceramic & presentable, I don't care.
>
>I'd be willing to trade TWO of my National 813-sized ceramic plate 
>caps
>(i.e. R.F.E.---"Removed From Equipment") for your two 807/224-sized 
>ceramic
>plate caps.
>
>Anything out there...?
>
>BTW, the behemoth is done---but NOT working (naturally!). The audio 
>stages
>are FB, but little else. NOW comes the learning process...! I'm 
>working
>backward from the detector stage on up to see what gives.
>
>It is one HEAVY mutha'! Good lookin', too, in a roaring 20's kind of 
>way.
>Sure does look like it's hiding a lot of potential from me...with any 
>luck,
>I'll be able to unlock its secrets BEFORE the 1929 QSO Party...!
>
>May have some digital pix taken & available on the weekend, too, in 
>case
>anyone is interested---but I HATE taking shots of non-working gear...
>
>Thanks & my very
>
>~73~ Eddy VE3CUI - VE3XZ
>
>************************************
>Visit the HBR Receiver Web Site with over 100 pictures of receivers 
>and 
>construction notes...... via http://www.qsl.net/k5bcq/ 
>
>Retrieve reflector archived data via 
>http://mailman.qth.net/mailman/listinfo/hbr
>


From hbr@mailman.qth.net  Wed Nov 12 15:33:00 2003
From: hbr@mailman.qth.net (Mobile Engineering)
Date: Wed, 12 Nov 2003 09:33:00 -0600
Subject: [HBR] Items For SWAP...
In-Reply-To: <004401c3a917$4e7a84a0$dbd549c6@greg>
Message-ID: <5.2.1.1.2.20031112093152.02f7ea08@pop.hickorytech.net>

Hi,

I may have some plate caps. Please describe the dia. and length of the 
plate terminal to which they must connect.

73's,

John, K0YQX

At 07:09 AM 11/12/2003 -0500, Eddy Swynar wrote:
>Greetings All,
>
>I came up two items short here in my 1929 homebrew replica superheterodyne
>receiver project, specifically, two ceramic plate caps for my 224 globe
>tubes...
>
>Does anyone have a pair they'd like to part with...? They can be either
>National Radio type, or James Millen---as long as they're both white, glazed
>ceramic & presentable, I don't care.
>
>I'd be willing to trade TWO of my National 813-sized ceramic plate caps
>(i.e. R.F.E.---"Removed From Equipment") for your two 807/224-sized ceramic
>plate caps.
>
>Anything out there...?
>
>BTW, the behemoth is done---but NOT working (naturally!). The audio stages
>are FB, but little else. NOW comes the learning process...! I'm working
>backward from the detector stage on up to see what gives.
>
>It is one HEAVY mutha'! Good lookin', too, in a roaring 20's kind of way.
>Sure does look like it's hiding a lot of potential from me...with any luck,
>I'll be able to unlock its secrets BEFORE the 1929 QSO Party...!
>
>May have some digital pix taken & available on the weekend, too, in case
>anyone is interested---but I HATE taking shots of non-working gear...
>
>Thanks & my very
>
>~73~ Eddy VE3CUI - VE3XZ
>
>************************************
>Visit the HBR Receiver Web Site with over 100 pictures of receivers and
>construction notes...... via http://www.qsl.net/k5bcq/
>
>Retrieve reflector archived data via 
>http://mailman.qth.net/mailman/listinfo/hbr



From hbr@mailman.qth.net  Wed Nov 12 16:55:45 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Wed, 12 Nov 2003 11:55:45 -0500
Subject: [HBR] EUREKA!!! It WORKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Message-ID: <001101c3a93d$eeefd4a0$cdd549c6@greg>

Hi All,

Well, I am VERY happy to say that my homebrewed 12-tube 1929 superheterodyne
receiver project IS WORKING!!!!!!

I gave it the "maiden run" test voyage this morning---some problems
('natch!): an open plate choke, a bad solder connection on a bypass cap, and
not enough (and later too much!) coupling between the local oscillator & the
detector...the usual little stuff.

I still have to determine how many turns of the local oscillator coil I'll
have to short out in order to make it tune the 80-meter band (right now it
tunes from about 3.3 to 3.490-MHz---but I was wise enough from the get-go to
employ more coil stock turns than needed, "...just in case". It's always
easier to SHORT turns, rather than to try & ADD them later on, after the
fact!).

It purrs along every bit as loud as my FT-980 along side it (the rice rocket
is relegated to the role of digital frequency meter for these particular
tests). Signals definitely peak right up with the two pre-selector
capacitors (yup, it's a knob twiddler's delight!), & the old British vernier
dial assembly is as smooth as silk---BETTER than anything encountered from
either National, or Millen, surprisingly enough...

Surprised, too, by the absence of hum, & IF feedback in the thing---either
I'm really lucky, or I've managed to learn a trick or two in these matters
after homebrewing for some 32 years now.   :>)

The whole package LOOKS real sexy, too---with any luck, I may be able to
borrow a digital camera this weekend...if anyone cares to, I'd be more than
pleased to e-mail shots of my latest "pride & joy" here to them. Just ask!

Now, according to Murphy's law, the darn thing should blow up between now &
the first request for a shot...Hmmmmm.

~73!~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Wed Nov 12 18:08:33 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Wed, 12 Nov 2003 13:08:33 -0500
Subject: [HBR] EUREKA!!! It WORKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
In-Reply-To: <001101c3a93d$eeefd4a0$cdd549c6@greg>
Message-ID: <3FB230D1.16866.85B246@localhost>

CONGRATULATIONS Eddy!

How 'bout pictures on the web site?   This is a real achievement, a 
very nice piece of work, and an inspiration to the rest of us!   

Congratulations again!

Walt 
KJ4KV

From hbr@mailman.qth.net  Wed Nov 12 19:16:41 2003
From: hbr@mailman.qth.net (Jeff Noel)
Date: Wed, 12 Nov 2003 14:16:41 -0500
Subject: [HBR] EUREKA!!! It WORKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
References: <001101c3a93d$eeefd4a0$cdd549c6@greg>
Message-ID: <000801c3a951$81a49d40$db6a2c42@hppav>

Please, may I see the pictures!

Jeff

k4zku@erols.com


From hbr@mailman.qth.net  Thu Nov 13 11:34:47 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Thu, 13 Nov 2003 06:34:47 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 2
Message-ID: <3FB32607.29039.424A0F@localhost>

Two days of testing and adjusting a push-pull oscillator using 1U4's, 
the worm drive and dial from an LM frequency meter, and a split-
stator tuning cap from an unknown piece of military UHF gear yielded 
an interesting collection of things that worked and one that hasn't -- 
yet.

The oscillator works -- at 60 V on the plate it draws around 1 mA and 
delivers 5V p-p across a 270 mmf capacitor -- actually, two such 
waveforms of opposite phase.   It's -- wow! -- really stable.   The lash-
up version does all its drift in a couple of minutes and may then be in 
the under 100 cps/hour range, indefinitely.  The drift is quite steady, 
so with compensation it should be better.  There are too many loose 
ends to really evaluate it -- a couple of poor-quality fixed ceramic 
caps in there, the turns on the coil aren't glued down, long 'haywire' 
leads, no cover on the oscillator box, filament isn't perfectly filtered or 
bypassed ... you get the picture.   But I'm ready to say that providing 
well-filtered DC to the filament of an oscillator tube (or tubes in this 
case) might be a worthwhile price if you need really low warm-up drift! 

(Of course it's only worthwhile because essentially no other heat will 
reach the oscillator except throught the air and with everything in a 
closed box, it'll all warm up at the same rate.   With oscillator parts 
strewn over several inches and multiple other nearby tubes and 
conduction heating paths as in the 1MHBR, a battery-tube oscillator 
would make no significant difference.)

Other than a couple of bad fixed capacitors, there really were none of 
the usual circuit-doesn't-do-what-you-expect kinds of problems.   
Everything just needs a good clean up, and it'll be ready to go.

Except for the darn tuning capacitor.  It tunes over a range of about 
240 degrees and that was one of its great attractions because it 
allowed picking a 180 degree range without end effects.  To tune over 
240 degrees, the stator has to be only 120 degrees -- otherwise the 
rotor would start to reenter it as the capacitance was decreasing.   
120 degree stator, 240 degree rotor ... but with this arrangement, as 
you turn in the increasing capacitance direction the rotor starts to 
*exit* the stator somewhere near mid-position.   Suddenly the 
capacitance is going down at the same time it's going up, meaning a 
step-decrease in the rate of increase.   The manufacturer dealt with 
that by placing a step increase of the rotor radius at just the right 
place to make the difference.   As the backside of the rotor starts to 
exit the stator, the radius of the rotor suddenly increases to 
compensate. 

I looked at that a dozen times while building the unit and wondered 
... this was done long before computers were used for such things so 
how would you design this feature?   Graphical electric field 
methods?   Wild guess?  Cut and try?   Did they get it right?

Well ... not quite.   In general I was able to linearize the tuning (i.e., 
track it to the linear calibration of the LM dial) within about 200 cps; I 
suspect that with some further work it could be gotten down to 100 
cps.   However just ahead of the step in the rotor radius -- covering 
say 50 kcs of the 500 kcs tuning range I'm using -- they ramped out 
the radius substantially, well ahead of the point where the rotor exit 
occurs.   There's a 5 kcs 'kink' in the tuning (a dip in frequency) at 
that point.

Later today I'll make one pass, removing the tuning cap, removing the 
shaft over a large mixing bowl so the 100 or so itty-bitty ball bearings 
(rat shot size) go someplace where I can find them, and grinding or 
filing the contour of the rotor plates to correct the problem. Working 
by uncalibrated eyeball and since I'm unwilling to do more than a one-
shot effort, I can probably get the error to the 1 kcs range and 
squeeze most of that into a smaller tuning range.

(Unwilling -- two hours of very fussy work and if I drop that ceramic 
shaft, the game's over.  Once is going to be plenty.)

This wasn't a problem in the original because these UHF sets used a 
bunch of ganged identical caps and switch selected crystals.  You 
peaked the capacitor knob (or knobs) according to the crystal, 
locked everything up, and an autopositioner did the job the next time 
that channel was selected.    

I think that capacitor may be from the RDZ -- an amazingly heavy 
RCA 200-390 Mcs shipboard receiver dating from about 1946-7.   The 
corresponding transmitter was the TDZ, at something like eight the 
all-time high water mark for number of Collins Autotune units in one 
radio.   The system had nearly a negative lifecycle, as it was based 
on the use of fundamental crystals in the 5 Mcs range multiplied up 
in conventional doublers and triplers.   But a task force of ships could 
easily need 100 or more channels and there was such severe mutual 
interference with all the spurious frequencies that the Navy rushed a 
series of single-channel transmitters and receivers based on overtone 
crystals into production within a few years.   

The units showed up in surplus but there was little you could do with 
them -- you got any ideas for a 400 pound 10-watt UHF transmitter?   
The receiver wasn't so bad but still required two men and a boy to lift.

Walt 
KJ4KV

From hbr@mailman.qth.net  Sun Nov  9 13:30:26 2003
From: hbr@mailman.qth.net (Don)
Date: Sun, 9 Nov 2003 07:30:26 -0600
Subject: [HBR] Walt's project
Message-ID: <003301c3a6c5$a31c12c0$76526144@ok.cox.net>

As I am a solid state man myself for the most part I really hope I am =
not intruding in your website....

I don't recognize the tuning cap but I have one of those bulky drives =
from Walts latest pictures. Currently on an old 6 meter tube rig that =
was junked years ago. If you or someone else wishes to have it let me =
know....free of charge too.  Also I have a box of ceramic plug in coils =
which are buried in my attic. They are octal bases but might be used in =
your rig Walt. Some were for plate circuits for power amps as they have =
the plate cap on them. You could get away from the vagaries of plastic. =
Also I have some military quality plug in coils with bakelite bases. =
They are slug tuned from the bottom with a detachable metal shield on =
top. I think I took them out of an old military signal generator. The =
coil could/might be rewound and tapped for switching bands. Have two to =
give.

Finished my own tube receiver last spring......you tube guys are =
gluttons for pain!!! Ended up using ladder filters made from Mouser =
microprocessor crystals. Have a 400 Hz CW and and about 1500 Hz SSB =
switched filters. Worked Isreal and Korea (real lucky) and a bunch of JA =
CW this month using my HB VFO and 6AG7/6L6 30W transmitter. My wife =
checks on me every few minutes when I use my tube gear...she is sure she =
is going to find me twitching on the floor one of the days. I am also =
working on the matching SSB/CW transmitter a little each week. Was going =
to use the rx LO and mix to basic 40M freq and mix again to 20, 15, 10 =
but I could not find a 4MHz SSB filter. I could probably make one but =
only about 1500 Hz like my rx filter... but 4Mhz is a little low for =
that. I  decided to build the SSb transmitter with 9Mhz filter now and =
use an on board VFO at 1.5 to 2.0 Mhz and may change my rx to 9Mhz IF =
too. In my rx I have 3 to 3.45 Mhz LO now with 4Mhz IF for basic 40 =
meter rx. And since my RX is interstage transformerless it would not =
take long. The 9MHz will make SSb filter easier but the CW filter a =
little harder. Everthings a compromise.

Walt if you would or anyone else want any of the above let me know. Also =
I have a reasonably simple method for building a HB tuning drive using a =
mayonaise jar lid. Its the old shaft and pulley method. I wrote an =
article for an electronics magazine years ago describing it. Using an =
1/8" shaft and 3" lid you can get about 24:1. If you add a panel mounted =
in-line 5:1 epicylic drive you can get 120:1. In my rx I use something =
similar...a 1.75" pulley, 3/16" shaft in line with one of the 5:1 =
drives. Gives me about 50 or 60:1. I got the drive at Dan's Small =
Parts..also a good source for ceramic standoffs and feedthroughs. Also =
got my panel and the rx bottom at On-line metals like you Walt....came =
with a few scratches but the 3/8" panel even though a little thick adds =
a lot of mechanical stability when using the crappy aluminum chassis' =
available. If you haven't already found a chassis for your rig yet. I =
think Hammond transformer in Canada might have steel chassis'. If I ever =
built another tube station again (which I won't as I am going back to =
solid state...so much easier) I would have used one of the audio =
chassis' I see on the internet. Also I was at my brother in laws house =
in California and he has a commercial tube audio amp for his stereo. It =
was pretty cool as the chassis was modularly constructed. It was made up =
of pieces bolted to gether. The pieces seem to have been standardized in =
size and the side and tops  were screwed together. It was approx 10 x 13 =
and I pressed on it and it was rock stable yet appeared to be able to be =
taken apart and made narrower or wider if the amp was to be modified. =
The sides were about 3" tall and could not be changed but could be =
lengthened or shortened.

Hope I didn't butt into your web site too much. I would send pictures of =
my rig but I am definitely not in the true spirit of Kee's site. As Walt =
knows from e-mails several months ago my rx is and tx will be alot of =
solid state and I have no interstage transformers as I used toroids or =
miniature chokes for all plate chokes, LO coils, etc. Rx has or will =
have 16 solid state devices when the 20, 15, 10 convertors are done and =
the tx low level devices will all be solid state...I just didn't want =
plug in coils mostly....to much work!!  But I enjoy all of the tube rigs =
you guys are building. Wish I wasn't so scared of high voltage!!! The =
transmitter will use 400 volts on finals and that is as high as I have =
ever worked with on HB.

Don Kelly KA5UOS




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From hbr@mailman.qth.net  Thu Nov 13 04:09:39 2003
From: hbr@mailman.qth.net (Donald Chester)
Date: Thu, 13 Nov 2003 04:09:39 +0000
Subject: [HBR] Re: [AMRadio] Items For SWAP...
Message-ID: <BAY1-F137vsTDWWcuZc0000152c@hotmail.com>


>I came up two items short here in my 1929 homebrew replica superheterodyne
>receiver project, specifically, two ceramic plate caps for my 224 globe
>tubes...
>
>Does anyone have a pair they'd like to part with...? They can be either
>National Radio type, or James Millen---as long as they're both white, 
>glazed
>ceramic & presentable, I don't care.

I don't think they used white ceramic plate or grid caps back then.  All I 
have ever seen on gear of that vinage is the metal clips.  The ones made by 
National are called "National Grid Grips".  I believe the ceramic ones date 
from WW2 or later.

Don K4KYV

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From hbr@mailman.qth.net  Fri Nov 14 12:10:09 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Fri, 14 Nov 2003 07:10:09 -0500
Subject: [HBR] 1929-Style SUPERHET RECEIVER...
Message-ID: <001401c3aaa8$62030aa0$cbd549c6@greg>

Hi Everybody...

Many thanks to all who've taken the time to  direct kind words of
encouragement re. my recently-completed project---much appreciated!

As it turns out, I WILL, indeed, have access to a digital camera this
weekend: anyone who has asked for them SHALL receive a bunch of photos
through the e-mail on either Saturday, or Sunday...

I've also compiled a list of answers to specific questions asked by everyone
as to the design of this thing, what inspired me to build it, etc.---this
will be included with the photo attachments.
I'll send out everything to everyone in one big, blanket e-mail, due to the
sheer volume of interest shown in this thing. If it takes TWO separate
mailings to prevent servers from "giving up" (Hi), so be it!

If the effort might inspire even one single, solitary homebrewer to finally
"...come out of the closet" with soldering iron & Handbook in hand, it WILL
have been worth all the while! Hi Hi.

Now...please stay tuned...

~73!~ Eddy VE3CUI - VE3XZ

PS: Yes, it WOULD have been MUCH simpler were I to post everything on a
separate web site, but I can't even PRETEND to be that
computer-savvy---after all, it should be obvious by now that my head (and my
heart!) is still stuck in the Roarin' Twenties!   :>)


From hbr@mailman.qth.net  Fri Nov 14 14:54:16 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Fri, 14 Nov 2003 08:54:16 -0600
Subject: [HBR] 1929-Style SUPERHET RECEIVER...
Message-ID: <20031114.090008.-380147.0.windy10605@juno.com>

Eddy, please send me some pictures too and I'll put them on the website.
Thanks.

73 Kees K5BCQ

From hbr@mailman.qth.net  Sat Nov 15 21:10:32 2003
From: hbr@mailman.qth.net (George R. Griesbach)
Date: Sat, 15 Nov 2003 15:10:32 -0600
Subject: [HBR] FS-HB Transceiver
Message-ID: <NHBBKIJJOLOIFFNNPMBJGEEOEJAA.w5grg@comforttexas.net>

I have for sale a complete HB transceiver, PS and linear amp station.
Including A Speech processor, microphones (2), cables, frequency counter,
and manuals for all of it. It is a 2 band 80-160 transceiver. It uses
command set tuning controls, it is all SS , except the linear w/ 1x6146, and
1x 6CL6 driver. The transceiver could be used QRP or with the linear. It is
very selective and stable. The transceiver is 12vdc, and is powered by a
small supply on the back of the transceiver. The linear is powered from what
is labeled as a SB-1102 supply. I have changed the electrolytic in part of
the PS to get it functional. I have used the station on the air and have
gotten good signal reports without the speech processor. I did not check the
processor out, but I think it could stand recapping, also. I converted the
PS to a 3wire cord, and the rest of the station could stand that also. The
frequency counter makes some RFI in the transceiver, but I did not research
that, probably need s a few caps also. The manuals are pretty complete with
both schematics and written explanations of circuit theory. I will take
$300.00 + S&H. from 78013
Pictures are here;
  http://www.comforttexas.net/gallery/HB-Transceiver

email me and I will try to answer any questions, I have more of this hams
stuff I will put up later.
Thank You
George R. Griesbach W5GRG
505 River Oaks Rd.
Comfort, Texas 78013
w5grg@comforttexas.net
http://www.comforttexas.net/w5grg
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From hbr@mailman.qth.net  Sat Nov 15 21:42:40 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Sat, 15 Nov 2003 16:42:40 -0500
Subject: [HBR] My 1929 Retro-Superhet Receiver---THE QST SUPER 12
Message-ID: <001401c3abc2$7c7edd80$fdd549c6@greg>

Hi Gang,

Well, anyone who may have asked for photos of my retro-1929 superhet
receiver SHOULD have received them by now...

If not, do please give me a buzz, & I'll try again...

~73!~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Sat Nov 15 21:42:40 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Sat, 15 Nov 2003 16:42:40 -0500
Subject: [HBR] My 1929 Retro-Superhet Receiver---THE QST SUPER 12
Message-ID: <003201c3abc3$dd1ddc80$fdd549c6@greg>

Hi Gang,

Well, anyone who may have asked for photos of my retro-1929 superhet
receiver SHOULD have received them by now...

If not, do please give me a buzz, & I'll try again...

~73!~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Sun Nov 16 18:42:57 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Sun, 16 Nov 2003 13:42:57 -0500
Subject: [HBR] Al Feder...
Message-ID: <003401c3ac72$d516db40$c6d549c6@greg>

Hi Al,

I hope you're reading this...the e-mail I sent you bounced right back to my
server...

Please give me your exact e-mail address again, & I'll try sending the
photos of my "QST SUPER 12" to you again.

Thanks, & my very

~73!~ Eddy VE3CUI - VE3XZ


From hbr@mailman.qth.net  Sun Nov 16 19:52:35 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Sun, 16 Nov 2003 14:52:35 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 3
In-Reply-To: <3FB32607.29039.424A0F@localhost>
Message-ID: <3FB78F33.25850.1DE331F@localhost>

The tunable oscillator part of the job is about wrapped up.

Tracking the dial has been somewhat of a challenge.   I pulled the 
tuning cap apart (48 itty-bitty ball bearings, total, not 100!) and filed 
the rotor plates to (I thought) fix the 'kink.'  Two hours from starting, it 
was back together, bearing preload correct, and working -- the 5 kcs 
kink was only about 1 kcs smaller because I had misjudged the 
problem.   So after staring at the thing for a while I got out the Dremel 
and what they call an rotary file but is actually a sort of end mill.   I 
stuffed paper towels over the bearings, Sharyn held the vacuum 
cleaner nozzle, and I milled off the necessary part of the plates, a 
little at a time with the oscillator running so I could check progress 
frequently.  Got it down around a 500 cps error and decided to call it 
quits.   

Following that I started bending plates -- very little required, except 
near the low frequency end where there's another kink of about 1.5 
kcs.  (Pretty much an inevitable result of using a series padder to 
correct the curve of a cap designed for SLF over a 2:1 frequency 
range -- a three point fit is going to leave a pretty good size error 
somewhere.)  It may not be possible to bend plates to fix that 
because the slots in the plates are in the wrong place.   However the 
Dremel technique might work again.   That is, it would work but the 
plates are less stiff there and I'm not confident of being able to do the 
job without ruining the cap.   However I'll probably give it a shot in the 
next day or two and then do a final pass on linearization.   Except at 
the low end kink it's around +/- 200 cps, end to end -- good enough 
for now, since the real tuning range (which affects linearization) 
depends on the crystal filter frequency which won't be known 
precisely until the receiver is built.   

The crystals are nominal 6.5536 Mcs clock crystals.   That's the 
parallel resonant frequency, the series resonance will be below there, 
and the passband of a series-crystal ladder filter (I think this is right) 
starts at the series resonance and extends upwards toward the 
parallel resonance.   Does anyone have a good description of the 
process of building a ladder filter?   I've seen discussions but they 
always seem to leave out a couple of critical facts.  I've done it before 
but it'll go faster if I have directions!

Then I went through and rewired the oscillator, shortening leads and 
generally getting rid of the haywire.   On the first test of drift, the 
oscillator went down a couple of hundred cps, then up over a few 
hours by several hundred.   I had finished up the linearization with 
most of the coil space-wound so that was no surprise.  I took two 
turns off the coil which made it necessary to close wind most of the 
rest; drift was then down 200, back up 200 and more or less stable.   

(With windings about 2x diameter in length, a closewound coil on 
polystyrene form will increase in inductance as temperature 
increases; with about 1/4 or 1/3 of coil spaced slightly it will have a 
near zero coefficient, with more than that spacewound it will have a 
negative coefficient.   Because they don't expand much with temp 
increases, ceramic coil forms are *not* more stable for ordinary ham 
VFO purposes -- the form stays put but the wire expands and 
increases inductance.   But if you had to build an oscillator for an 
extreme temperature range (A B-17 on the ground in England maybe 
50 degrees, at 28,000 ft. about -10 ...) you'd want to go ceramic.)

200 cps down and back is perhaps tolerable, but could still be better. 
I poked around with my digital thermometer probe and found that the 
only tuned circuit part that heats very much was the coil -- about 2 
degrees.   That seemed to be divided between some self heating and 
(mostly) heat conducted from the 39k resistor connected to the 
center tap.  (1 mA, 39k, 39 mW -- it doesn't take much if it's 
connected to a critical part!)    I split the resistor into 10k for isolation 
located in the box and 27k below the chassis, bypassing the 
junction.  (I didn't formerly have proper isolation there but obviously 
have to have it to use the oscillator in a receiver.)   Also reoriented 
the resistor from long axis vertical to axis horizontal, for better 
cooling.   Warm up drift seems to be less, but I'll have to let it get 
stone cold to be sure.   

The only other part that heats at all is a fixed capacitor of 15 mmf 
that's across the coil.   This is an NP0 cap, but those are almost 
never precisely '0' so it's best to keep them as cool as possible.  I 
only had a tiny one; I can either order a physically larger unit or use 
four 3.9's in parallel.  Humm ... I also could use a larger cap on the 
other side of the series padders, that is, across the tuning cap.   
That's much futher from the tube sockets so less temp increase and 
also a lower voltage point.

The downward drift is the tubes.   Once the upward drift is minimized 
I can put a compensating cap right on the tube socket.

The next question is "What's the rest of the front end going to look 
like"?   

My idea of a mixer with one input push-pull and the other single 
ended, output single ended, won't work.   A mixer can be thought of 
as a circuit that multiplies the two inputs so (say) negative x negative 
= positive.   Thus output of one mixer can be added (hooked in 
parallel with) that of a second mixer with positive x positive inputs.  
But negative x negative added to negative x positive -- the outputs 
cancel.  (Jim, I think you tried to say this ...)   Basically two of the 
three connections to a two-device (singly balanced) mixer have to be 
push pull and the other must be single end.  I have to either to go 
push-pull for one input and single ended for the other with output 
push-pull, or use two push-pull inputs and single-ended output.

I only have one tuning cap section available to tune the output, and 
the signal mixer I was planning (from the G2DAF Mk II) expects 
single end input.   That favors a premixer that's push-pull on both 
inputs, allowing single end output.   But I don't know about a Hahnel 
circuit with push-pull output ... that would likely require more than 
one envelope.

Alternative:  Go with the push-pull VFO, a single ended Hahnel input, 
take the premixer output push-pull using a separate winding for 
tuning.   More band switching that way.   Could either use single 
ended output or push-pull.

In between alternative -- if you ground one grid of a (say a dual triode) 
mixer, float the cathode, and drive the other grid, you get much of the 
effect of a push-pull input.   That is, all the phase relationships work --
the only thing you don't get is full cancellation of the input in the 
output circuit.  (The total cathode current has to vary at signal rate to 
get opposite grid-cathode voltage changes, so the total plate current 
must vary similarly.

Another interesting fact -- the 6BN6 gated beam tube has 
outstanding linearity on either input.   I'm guessing they can't be 
used as signal mixers because of high noise levels but they ought to 
work fine as premixers with 100 mV or larger ignals from both 
oscillators.   And unlike the beam deflection tubes, the electrode 
voltages are reasonable.   So two 6BN6's with G3 driven push-pull 
(the VFO) and one G1 driven single end (Hahnel) with the other G1 at 
signal ground could have the plates in parallel.   The VFO gets the 
full benefit of balanced mixer design, the Hahnel only gets some, but 
those signals are always 5 Mcs on the high side of the desired 
output frequency -- fundamental is relatively easy to get rid of and 
harmonics are a non-issue.  And you have single ended output.

There is outstanding info on 6BN6 performance in a product detector 
in the article "Some Ideas in a Ham-Band Receiver," Arnold & Allen, 
QST, May 1960, reprinted in "SSB for the Radio Amateur", 1965 
copyright.

Definitely time for the next round of headscratching!

Walt
KJ4KV



From hbr@mailman.qth.net  Mon Nov 17 11:59:04 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Mon, 17 Nov 2003 06:59:04 EST
Subject: [HBR] Yet Another HBR Project -- Chapter 3
Message-ID: <1a6.1ce388eb.2cea1208@aol.com>

In a message dated 11/16/03 2:53:52 PM Eastern Standard Time, 
waltah@earthlink.net writes:


> My idea of a mixer with one input push-pull and the other single 
> ended, output single ended, won't work.   A mixer can be thought of 
> as a circuit that multiplies the two inputs so (say) negative x negative 
> = positive.   Thus output of one mixer can be added (hooked in 
> parallel with) that of a second mixer with positive x positive inputs.  
> But negative x negative added to negative x positive -- the outputs 
> cancel.  (Jim, I think you tried to say this ...)  

Yeah, that's basically what I was getting at. But it's worth looking at all 
kinds of configurations - that's how the Tayloe mixer came about.

 Basically two of the 
> 
> three connections to a two-device (singly balanced) mixer have to be 
> push pull and the other must be single end.  I have to either to go 
> push-pull for one input and single ended for the other with output 
> push-pull, 

I think that's what G2DAF did

or use two push-pull inputs and single-ended output.
> 
> 
I'm not sure that will work. Here's why:

"Inputs in pushpull" really means "180 degrees apart". So you have Mixer Side 
1 and Mixer Side 2 operating identically except everything in Mixer Side 2 is 
180 degrees shifted (out-of-phase) from Mixer Side 1 and viceversa.

So their outputs are ideally exactly 180 degrees out of phase 
and...cancellation. 


> I only have one tuning cap section available to tune the output, and 
> the signal mixer I was planning (from the G2DAF Mk II) expects 
> single end input.   That favors a premixer that's push-pull on both 
> inputs, allowing single end output.   But I don't know about a Hahnel 
> circuit with push-pull output ... that would likely require more than 
> one envelope.
> 

See above.


> Alternative:  Go with the push-pull VFO, a single ended Hahnel input, 
> take the premixer output push-pull using a separate winding for 
> tuning.   More band switching that way.   Could either use single 
> ended output or push-pull.
> 

Mo' bettah.

> In between alternative -- if you ground one grid of a (say a dual triode) 
> mixer, float the cathode, and drive the other grid, you get much of the 
> effect of a push-pull input.   That is, all the phase relationships work --
> the only thing you don't get is full cancellation of the input in the 
> output circuit.  (The total cathode current has to vary at signal rate to 
> get opposite grid-cathode voltage changes, so the total plate current 
> must vary similarly.
> 
> Another interesting fact -- the 6BN6 gated beam tube has 
> outstanding linearity on either input.   I'm guessing they can't be 
> used as signal mixers because of high noise levels but they ought to 
> work fine as premixers with 100 mV or larger ignals from both 
> oscillators. 

I've got a big jar of them somewhere and I'd love to know how that works for 
you.

  And unlike the beam deflection tubes, the electrode 
> 
> voltages are reasonable.   So two 6BN6's with G3 driven push-pull 
> (the VFO) and one G1 driven single end (Hahnel) with the other G1 at 
> signal ground could have the plates in parallel.   The VFO gets the 
> full benefit of balanced mixer design, the Hahnel only gets some, but 
> those signals are always 5 Mcs on the high side of the desired 
> output frequency -- fundamental is relatively easy to get rid of and 
> harmonics are a non-issue.  And you have single ended output.
> 

Nice!


> There is outstanding info on 6BN6 performance in a product detector 
> in the article "Some Ideas in a Ham-Band Receiver," Arnold & Allen, 
> QST, May 1960, reprinted in "SSB for the Radio Amateur", 1965 
> copyright.
> 

I tried that detector years ago, and it works. But as the authors warn, it's 
microphonic. I went to a 6GX6 self-excited xtal BFO/detector (a la Drake)
for the Type 7


> Definitely time for the next round of headscratching!
> 
Paper is cheaper than aluminum.

One question on the pushpull 1U4 VFO: Will it have enough output to be 
useful?

73 de Jim, N2EY


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From hbr@mailman.qth.net  Tue Nov 18 02:16:00 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Mon, 17 Nov 2003 21:16:00 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 3
In-Reply-To: <1a6.1ce388eb.2cea1208@aol.com>
Message-ID: <3FB93A90.5272.22A9C6E@localhost>

The oscillator kept drifting up more than I thought it should, also it 
was just a little unstable, wandering a few cps one way, a few, the 
other without apparent reason.   Applying the 'hot soldering iron tip 
under various parts' technique, I found that the 15 mmf fixed cap 
across the tank was not NP0 as labled, but N ... some fairly large 
number.  Swapping it for 4 3.9 NP0's in parallel fixed both problems.   
This combination has a slight positive coefficent -- but it is *slight*.   
The other cap must have been breaking down.  There's 50V p-p 
there, but evidently it was too much for that nominal 100V cap.  I like 
to use 500V or 1KV caps in these jobs but this time I didn't have 
one.  

Now it goes down about 100 cps in 5 minutes, then back up 120 in 
an hour and a half -- not sure if it's stable yet or not, but it's very 
close.  And there are a couple of other parts I haven't checked out 
yet.  

Jim said:
> "Inputs in pushpull" really means "180 degrees apart". So you have Mixer
> Side 1 and Mixer Side 2 operating identically except everything in Mixer
> Side 2 is 180 degrees shifted (out-of-phase) from Mixer Side 1 and
> viceversa.
> 
> So their outputs are ideally exactly 180 degrees out of phase 
> and...cancellation. 

Naw ... think *multiplier* -- a mixer is a *multiplier*.   In the described 
case, + times + = +, and - times - = +  so the outputs add.   (I'm 
neglecting the phase reversal of vacuum tubes ...)

You are focussing on the outputs resulting from the amplification of 
the input signals.   Those do indeed cancel -- that's the beauty of the 
doubly balanced mixer.   But the desired mixing products add.  

One of the few useful things in recent Amateur's handbooks is the 
detailed discussion of theory in reasonably plain language.   There's 
a chapter on mixers and some other stuff -- chapter 15 in my 1995 
book; the first couple of pages of that might clear things up.

Yet another way to see it:  Imagine a perfect mixer, i.e., no distortion 
occurs on either signal path.   (A beam tube is close, within its limits 
-- a very linear pentode amplifier with a second input that swings the 
electron beam from one plate to the other.)   Put the same exact 
signal in on both inputs:  what comes out?   If you draw two sine 
waves in phase and sketch the result from multiplying them together, 
you can see -- a sine wave at 2x the frequency, superimposed on a 
DC component.   (f + f = 2f and f - f = 0 in the frequency domain.)  
Now considering combining the output of two single ended mixers, 
the output at the plate receiving the two positive signals is *identical 
to* but 180 degrees out of phase compared to the other plate sure 
enough -- but at twice the frequency the 180 input degrees becomes 
360 degrees, i.e., in phase.   So the outputs can indeed be paralleled.

I admit to being unable to quickly find an example of the type circuit 
I'm considering in the literature but I think its just that hams didn't 
build a lot of complex vacuum tube circuitry.   

One practical example is the 'push-push' mixer I use all the time -- 
plates and cathodes in parallel, each input single ended on one grid.  
It's not really push-push at all, but push-pull for both signals on the 
same two grids because each grid input causes a cathode voltage 
change that is equivalent to a reverse phase input at the opposite 
grid.  Works like a champ, and if you used a pair of two grid tubes 
(with plates similarly in parallel) and applied one push-pull input on 
each pair of grids, it would be even better -- doubly balanced, which 
is the 'there is nothing better' of mixers.

The mixer tube I want could have been provided in a single 9-pin 
envelope. One cathode connection, two G1's, a G2 for both sections, 
2 G3's and 1 plate connection for both; total seven pins allowing two 
for the filament.  Unfortunately the tube manufacturers didn't see fit to 
do so. Of course since I'm the only one with an application maybe 
they didn't see this as a really big market.

A pair of 6BN6's should be ideal -- I can't see how slight 
microphonism would be a problem in this application.  Hahahaha ...

Quoting myself:

>> But I don't know about a Hahnel circuit with push-pull output ...
>> that would likely require more than one envelope.

The late news is that with some doodling I've come up with an  
elegant circuit giving push-pull output.  Namely a push-pull dual 
triode free running oscillator with a crystal connected as a *parallel* 
plate to grid (Pierce) oscillator.   

The circuit:  Coil plate to plate, center tapped for HV.   Each plate to 
opposite grid via small cap, bigger cap grid-to-ground.   (A 1:5 ratio of 
plate to grid voltages seems to work well.)  Cathode grounded.   
That's your basic push-pull oscillator, though I don't know the name 
of the circuit.   (It's a kalitron with added grid to ground caps.)   Now 
put a choke (or large resistor) in the plate HV connection and 
connect one end of the crystal to the tap on the coil.   Lift the 
grounded ends of the two grid-to-ground caps, join them, add another 
cap from there to ground and connect the other end of the crystal to 
the junction of the three caps. 

Should operate as a crystal oscillator with the tube sections in 
parallel on a frequency at which the crystal appears inductive and 
push pull on a frequency determined by the tuning of the tank, but 
with a strong locking effect since the two grids are pulsed in phase 
by the crystal.   You might think the synch pulses would cancel out, 
but one of the grids is below cutoff, so only the conducting tube sees 
the pulse.   

Interestingly this circuit should lock at 1/2 Fc, Fc, 1-1/2 Fc, and so 
on -- but I can't think of a use for that feature in this application.   

Strictly speaking it could either be a Hahnel or just a locked 
oscillator, depending on how it's adjusted.   The Hahnel is a *keyed* 
oscillator -- oscillation completely stops at the output frequency for a 
brief period determined by the crystal frequency.   But a locked 
oscillator can run continuously, with the crystal signal simply 
advancing the phase very slightly on each cycle -- i.e., the free 
running oscillator must be adjusted to a frequency slightly below the 
desired multiple.   Both types generate spurious outputs in the form 
of a spectrum of harmonics of the crystal frequency but it seems to 
me that the locked oscillator would have the better purity of the two.   
However, it is subject to jumping to another multiple if misadjusted, 
for example, as the tank circuit drifts.   The Hahnel, OTOH, would 
decrease output at the desired frequency and increase it at the 
incorrect multiple.  In a particular application, I suppose one bad 
behavior might be less bad than the other.   Anyhow, you don't get 
away from building stable circuitry by using either concept.

I don't see anything wrong with it, but I had two (former) marriages 
that I saw nothing wrong with beforehand ... I b'lieve I'll breadboard 
the oscillator rather than commit to it indefinitely at this point.   
Hopefully tomorrow.   I see a place on the VFO test chassis with 
holes for a 9-pin socket and a crystal socket ...

> One question on the pushpull 1U4 VFO: Will it have enough output to
> be useful?

5V p-p across a 270 mmf cap.  Since that's the grid-to-ground cap of 
the push-pull oscillator, there's 10V p-p grid-to-grid.   Way more than 
enough for a 6BN6 mixer ('bout 0.5V p-p for that), plenty for any 
ordinary mixer circuit (a couple of volts is usually ample) and well on 
the way to enough to use a beam tube mixer, if I wanted to.   Which I 
don't.   And that's with 60 volts on the plates -- I could raise or lower 
that, as needed to adjust the output.   

I really like push-pull oscillators.   More parts are needed and the 
tuning cap is 'more special' but the gain of the two tubes adds and 
the symmetry largely kills off even harmonics, making pure output 
easier to achieve.   Same advantages, actually, as push-pull 
anything else in a receiver.   

Jim (and occasional others), the continued critique is much 
appreciated!

Walt 
KJ4KV

From hbr@mailman.qth.net  Tue Nov 18 22:22:36 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Tue, 18 Nov 2003 17:22:36 -0500
Subject: [HBR] Re: My 1929 Retro-Supehet (the "QST SUPER 12")...
In-Reply-To: <001301c3abc1$89168c60$fdd549c6@greg>
Message-ID: <3FBA555C.6907.1C126D7@localhost>

Eddy, that's *beautiful*!

Walt
KJ4KV

From hbr@mailman.qth.net  Wed Nov 19 00:10:10 2003
From: hbr@mailman.qth.net (Byron Tatum)
Date: Tue, 18 Nov 2003 18:10:10 -0600
Subject: [HBR] FS- LF Collins Filters
Message-ID: <001c01c3ae31$806b92f0$bcd4dacf@your6jnhhu0520>

Hello-
    For sale one lot of low freq. Collins mech. filters total 8 pieces :
    # 522 - 9203 - 002 qty. 2
    # 522 - 9103 - 002
    # 526 - 9135  -  00
    # 522 - 9192 - 002 qty. 2,   70 Khz. CF, 3.42 Khz. wide @ - 6 dB.
    # 526 - 9200 - 00
    # 522 - 9138 - 002
    # 522 - 9204 - 00  76 Khz. CF, 625 Hz. wide @ - 6 dB.
    # 522 - 9194 - 002 78 Khz. CF, 3.46 Khz. wide @ - 6 dB.
            All 10 for 50.00 plus shipping.Most appear unused.Thanks, =
Byron

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From hbr@mailman.qth.net  Wed Nov 19 11:27:10 2003
From: hbr@mailman.qth.net (Diane Swynar)
Date: Wed, 19 Nov 2003 06:27:10 -0500 (EST)
Subject: [HBR] Re: My 1929 Retro-Supehet (the 'QST SUPER 12')...
In-Reply-To: <3FBA555C.6907.1C126D7@localhost>
References: <3FBA555C.6907.1C126D7@localhost>
Message-ID: <9414.198.208.159.14.1069241230.squirrel@webmail.durham.net>

Walt...

Many thanks!

As they say, it's got a face only a MOTHER could love---and even then, only
on PAY DAY...!  Hi Hi

~73!~ Eddy VE3CUI - VE3XZ





> Eddy, that's *beautiful*!
>
> Walt
> KJ4KV
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
>  construction notes...... via http://www.qsl.net/k5bcq/
>
> Retrieve reflector archived data via
> http://mailman.qth.net/mailman/listinfo/hbr




From hbr@mailman.qth.net  Wed Nov 19 13:42:29 2003
From: hbr@mailman.qth.net (Diane Swynar)
Date: Wed, 19 Nov 2003 08:42:29 -0500 (EST)
Subject: [HBR] 1929-Style "QST SUPER 12" Receiver: UPDATE
Message-ID: <2563.198.208.159.14.1069249349.squirrel@webmail.durham.net>

Well, to anyone complating the construction of a receiver like this
utilizing ancient tubes---or ANY tubes, probably, for that matter---do not
always suspect the worst when trouble-shooting...!

Two cases in point: the CW & SSB signals on my newly-minted retro-receiver
sounded harsh, rough, & just plain AWFUL...I re-built the BFO with a new IF
transformer---same thing. I was considering yet ANOTHER re-build of the
BFO, when it dawned on me that the signals sounded an awful lot like those
CW/SSB sigs through my old Hallicrafters S-77A on 10-meters.

Well, the local oscillator on the S-77A is just terrible above anything
much higher that 14-MHz, or so---sure enough, I monitored my BFO signal on
a nearby Yaesu FT-980: sounded clean...perfect! Next, I monitored the local
oscillator frequency on the '980: shades of the old S-77A!

Now, what to do..? I added RF chokes to the plate lead of the 224 balloon
oscillator tube: no difference. Next, I make-shifted a shield for the same
tube: nil. Finally, I swapped in a newer shoulder-type envelope 224A and---
PRESTO!---the oscillator was as stable as the BFO.

Next problem: a very high, scratchy, ambient noise level coming out of
the 'phones. I started to pull out tubes from the audio driver on up, to
localize it. PRESTO! ANOTHER 224A balloon tube in the detector was the
culprit! I replaced it with another ST 224A---PROBLEM GONE.

The moral of the story is simply this: even if your tubes pass muster on a
dynamic tube tester, it is NOT an accurate indication of how they'll
perform "...in the field". Both of these old 224A's were NOISEY in their
specific applications, for whatever reason(s)---and yet both had
transconductance levels just in excess of 800 umhos.

I don't particularly like using the more modern "ST" tubes in a 1929
design, but then again, I *DO* want to use the dog gone thing! Guess I'll
just kepp my eyes peeled for MORE globe/balloon 224A's in the future, & use
the process of elimination as to which will be "keepers"...

So far it's been a real blast with this behemoth on the bench...before
setting it up alonside my 3x227 MOPA, though, I want to run experiments
with regenerative feedback on both IF stages---looks EXTREMELY promising!

Stay tuned...

~73!~ Eddy VE3CUI - VE3XZ (that's "c3CUI" & "c3XZ" to anyone REALLY old
enough to remember! Hi Hi)



From hbr@mailman.qth.net  Wed Nov 19 17:05:57 2003
From: hbr@mailman.qth.net (Dan Merz)
Date: Wed, 19 Nov 2003 09:05:57 -0800
Subject: [HBR] 1929-Style "QST SUPER 12" Receiver: UPDATE
References: <2563.198.208.159.14.1069249349.squirrel@webmail.durham.net>
Message-ID: <3FBBA2F5.BB48E42@3-cities.com>

Hi Eddy,  thanks for the info on ST vs. globe 24's.  I have a number of  sets from
the late 20's/early 30's that use 24's but never made a systematic study of
comparing the two types of tubes.  I always liked the ST's when trying to get the
most out of a set and found that 01A's seemed to do a better job when the ST's were
used despite having "good" tubes,  (from a tube tester) in both cases.  But most of
this comparison was on much lower frequency broadcast band.   I would like to see
your set - did the pic's get posted somewhere - or are you sending to individuals?
best regards,  Dan

Diane Swynar wrote:

> Well, to anyone complating the construction of a receiver like this
> utilizing ancient tubes---or ANY tubes, probably, for that matter---do not
> always suspect the worst when trouble-shooting...!
>
> Two cases in point: the CW & SSB signals on my newly-minted retro-receiver
> sounded harsh, rough, & just plain AWFUL...I re-built the BFO with a new IF
> transformer---same thing. I was considering yet ANOTHER re-build of the
> BFO, when it dawned on me that the signals sounded an awful lot like those
> CW/SSB sigs through my old Hallicrafters S-77A on 10-meters.
>
> Well, the local oscillator on the S-77A is just terrible above anything
> much higher that 14-MHz, or so---sure enough, I monitored my BFO signal on
> a nearby Yaesu FT-980: sounded clean...perfect! Next, I monitored the local
> oscillator frequency on the '980: shades of the old S-77A!
>
> Now, what to do..? I added RF chokes to the plate lead of the 224 balloon
> oscillator tube: no difference. Next, I make-shifted a shield for the same
> tube: nil. Finally, I swapped in a newer shoulder-type envelope 224A and---
> PRESTO!---the oscillator was as stable as the BFO.
>
> Next problem: a very high, scratchy, ambient noise level coming out of
> the 'phones. I started to pull out tubes from the audio driver on up, to
> localize it. PRESTO! ANOTHER 224A balloon tube in the detector was the
> culprit! I replaced it with another ST 224A---PROBLEM GONE.
>
> The moral of the story is simply this: even if your tubes pass muster on a
> dynamic tube tester, it is NOT an accurate indication of how they'll
> perform "...in the field". Both of these old 224A's were NOISEY in their
> specific applications, for whatever reason(s)---and yet both had
> transconductance levels just in excess of 800 umhos.
>
> I don't particularly like using the more modern "ST" tubes in a 1929
> design, but then again, I *DO* want to use the dog gone thing! Guess I'll
> just kepp my eyes peeled for MORE globe/balloon 224A's in the future, & use
> the process of elimination as to which will be "keepers"...
>
> So far it's been a real blast with this behemoth on the bench...before
> setting it up alonside my 3x227 MOPA, though, I want to run experiments
> with regenerative feedback on both IF stages---looks EXTREMELY promising!
>
> Stay tuned...
>
> ~73!~ Eddy VE3CUI - VE3XZ (that's "c3CUI" & "c3XZ" to anyone REALLY old
> enough to remember! Hi Hi)
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
>
> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr



From hbr@mailman.qth.net  Mon Nov 24 13:43:54 2003
From: hbr@mailman.qth.net (Diane Swynar)
Date: Mon, 24 Nov 2003 08:43:54 -0500 (EST)
Subject: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript
Message-ID: <41695.198.208.159.14.1069681434.squirrel@webmail.durham.net>

Well, the receiver is ready for the upcoming 1929 QSO Party...in fact, all
I have to do, really, is button down the bottom cover & it's off to the
races!

Since sharing the pix with everyone, I've re-built the detector AND the BFO-
--changed some component values around, is all. I've also made the two
regenerative controls (one per IF stage) operational---what an improvement
in sensitivity AND selectivity!

On AM, signals just seem to "plop" into the passband---they peak incredibly
sharp, too, but with no lack of definition: fidelity remains A-OK. I'm
happy that I incorporated an HQ-170-style large-knobbed "fine tuning"
control, though...makes all the difference in the world.

When peaked-up right on CW, one DEFINITELY experiences near classic single
signal selectivity: the past weekend saw an "LZ" DX contest going down on
80-meters, & I merrily logged several stations from east Europe, with no
problems from QRM whatever. Just as described in the ARRL's first edition
of UNDERSTANDING AMATEUR RADIO (pp. 142-143), signals peak up beautifully.

What a joy! I can't describe to you the feeling one gets when a rag tag
collection of ancient bottles & components like this come together &
facilitate communications-quality signals like that...why EVERYONE doesn't
homebrew even a simple item for daily use in the shack is lost to me. Ham
Radio just wouldn't be Ham Radio without the ability to "...roll my own" in
this manner.

Thanks so much for letting me share this with the group---and now do,
please, get something on the air for the two weekends of the AWA Bruuce
Kelley 1929 QSO Party, so that the QST Super 12 might hear YOUR signal!
It's TWO weekends in duration, back-to-back, starting THIS COMING SATURDAY
NIGHT. It starts at 6:00 PM Saturady evening (that's 6:00 PM EST---2300
UTC), & ending at 6:00 PM SUNDAY evening. Frequencies generally are from
3550- to about 3580-KHz. Maximum input of 10-watts, with the exception of
after midnight, when 20-watts is allowed.

Close your eyes on the dawn of the vent, & imagine yourself to be sitting
next to a big millpond in the Spring---you'll know we're there from all of
the chirps, yoops, beches, groans, & buzzes that the old buzzard rigs are
famous for emanating forth! Hi Hi.

See you then...?

~73!~ Eddy VE3CUI - VE3XZ



From hbr@mailman.qth.net  Mon Nov 24 18:45:45 2003
From: hbr@mailman.qth.net (Jeff Noel)
Date: Mon, 24 Nov 2003 13:45:45 -0500
Subject: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript
References: <41695.198.208.159.14.1069681434.squirrel@webmail.durham.net>
Message-ID: <000c01c3b2bb$43c02440$8d732c42@hppav>

Eddy,

I know how you feel about your 29 rx.  You should be proud of it. I felt the
same way about the HBR 16 that I built. It also rose out of the junk box of
stuff and  now it plays. I would like to build a 29er
but lack parts that old. But I am thinking about another HBR though. I know
the guys with the super micro rigs will scuff at us that are still working
with glow plugs
but that is OK. This is what we like to do.

Jeff

K4ZKU



From hbr@mailman.qth.net  Mon Nov 24 23:10:36 2003
From: hbr@mailman.qth.net (Eddy Swynar)
Date: Mon, 24 Nov 2003 18:10:36 -0500
Subject: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript
References: <41695.198.208.159.14.1069681434.squirrel@webmail.durham.net> <000c01c3b2bb$43c02440$8d732c42@hppav>
Message-ID: <006801c3b2e1$342dac20$c2d549c6@greg>

Hi Jeff...

Congrats on that HBR-16 you built! No easy task, to be sure...

Well, I also own a "computer aided transceiver" Yaesu FT-980, AS WELL AS an
Icom 751A---both very FB high-tech rigs with their own merits---and yet I
feel as comfortable operating them as I do tinkering with the innards of my
other old "junque".

I think that's where we have it over those high falutin' appliance operators
out there: we can appreciate the merits of ALL generations of rigs, whereas
some of those guys are just too narrow-minded to do so...

Anyway, Jeff, I'm just glad that we are who we are...! Hi Hi

~73!~ Eddy VE3CUI - VE3XZ






----- Original Message -----
From: "Jeff Noel" <k4zku@erols.com>
To: <hbr@mailman.qth.net>
Sent: Monday, November 24, 2003 1:45 PM
Subject: Re: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript


> Eddy,
>
> I know how you feel about your 29 rx.  You should be proud of it. I felt
the
> same way about the HBR 16 that I built. It also rose out of the junk box
of
> stuff and  now it plays. I would like to build a 29er
> but lack parts that old. But I am thinking about another HBR though. I
know
> the guys with the super micro rigs will scuff at us that are still working
> with glow plugs
> but that is OK. This is what we like to do.
>
> Jeff
>
> K4ZKU
>
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
>
> Retrieve reflector archived data via
http://mailman.qth.net/mailman/listinfo/hbr


From hbr@mailman.qth.net  Tue Nov 25 01:04:08 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Mon, 24 Nov 2003 20:04:08 -0500
Subject: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript
In-Reply-To: <000c01c3b2bb$43c02440$8d732c42@hppav>
Message-ID: <3FC26438.19518.95CAEF@localhost>

Jeff Noel wrote:

> I know the guys with the super micro rigs will scuff at us that are
> still working with glow plugs but that is OK. 

They're just jealous ...

Actually, the truth is that one of the very nice things about ham radio 
is that there are a bunch of related hobbies in there.   DX, 
ragchewing, emergency preparedness, traffic handling -- and building 
new 'vintage' equipment.   It's really foolish, the food fights that 
sometimes get started between one group and another.  

Oh, and BTW, not all of those super micro rigs will outperform a well 
designed 1970 +/- vacuum tube rig.   The only thing that put the FT-
101 clearly ahead of a good vacuum tube transceiver was its size 
and weight -- it was in nearly all respects a marginal performer.   But 
it was solid state, and that was where the marketplace wanted to go.

Walt
KJ4KV


From hbr@mailman.qth.net  Tue Nov 25 01:22:35 2003
From: hbr@mailman.qth.net (Jeff Noel)
Date: Mon, 24 Nov 2003 20:22:35 -0500
Subject: [HBR] 1929 "QST SUPER 12" Retro-Receiver---Postscript
References: <3FC26438.19518.95CAEF@localhost>
Message-ID: <000401c3b2f2$b1d71b00$1e762c42@hppav>

Well, so I won't be left out of the micro rigs. I have a Yaesu FT1000MP MARK
V and a TenTec Omni VI+
for a back up.

Jeff



From hbr@mailman.qth.net  Thu Nov 27 02:40:49 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Wed, 26 Nov 2003 21:40:49 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 4
In-Reply-To: <3FB93A90.5272.22A9C6E@localhost>
References: <1a6.1ce388eb.2cea1208@aol.com>
Message-ID: <3FC51DE1.21445.293DF8C@localhost>

A change of plans ...

After some further work, the VFO is nearly finished.   When turned 
on it goes down maybe 150 cps in 10 minutes, then drifts very 
slowly, remaining within +/- 50 cps indefinitely.   The variation seems 
to be due to changes in room temperature; it's lower at night, higher 
in the day; the reversal of direction since last report is caused by 
redoing the coil so it's mostly not spacewound.    I could probably 
rewind it yet again and come even closer, but this will do for now.   
Changing the capacitor compensation is easier -- I may do that.

I will again disassemble the tuning cap so I can trim the rotor plates 
slightly to get rid of the 1.5 kcs kink near the low end.   

Now to the matter of the crystal part of the premixed injection signal.  
Sometimes just thinking about the problem works as well as 
grabbing a soldering iron.   The trouble with locked oscillators is that 
it's darn near impossible to be sure they'll lock on the right multiple if 
that multiple is more than two or three.   I need about 8 at the low 
end, about 24 at the high one.   *That* was the problem solved by the 
Hahnel circuit -- since nothing is locked, it can't lock on the wrong 
frequency.  The worst that happens is you produce more than a 
desired minimum of output on an adjacent multiple and slightly less 
on the right one.

However, the key distinction (between locked and Hahnel designs) is 
that in the Hahnel circuit, oscillation entirely stops for every cycle of 
the controlling (crystal) signal, and then restarts.   The time required 
for this is proportional to Q of the oscillator tank circuit -- lower Q's 
are desired for a quicker stop and restart so you can actually get 
some cycles of the desired frequency before the next stop time.  

In other words, oscillation at the desired frequency is 100% 
modulated by the controlling signal.   That means you are producing 
half the total power on other frequencies -- the quicker the stop and 
start, the more big sidebands are out there.   To get rid of those, you 
need high Q circuits, but the oscillator tank can't be one of them.   
So, you need amplifiers and ganged high-Q circuits to follow.   The 
handbook I mentioned shows a circuit which is claimed to keep 
sidebands 40 db below the desired frequency with a single tuned 
amp stage.  Maybe, but it sure doesn't look as easy as it once did.   

There's a reason the military paid for this work and then never did 
anything with it.   All the multi-channel sets I've studied either used 
individual crystals (the WW-II approach) or some form of crystal 
synthesis, usually direct in the early days.   Indirect (a tunable 
oscillator phase locked to a crystal synthesized signal) began to 
take over around the early 60's, as SSB became the norm for long 
range military voice communications. 

I've done a little work with locked oscillators -- it's no problem to get it 
on the right multiple but getting it to lock there again when the set is 
switched off and then switched on again after getting cold, is a real 
challenge.   And if I'm going to have to use two narrowband tuned 
amps following the Hahnel circuit (they have to be narrow if they're 
going to cut out those sidebands) ... 

I think I'm not going down either path.  What are the alternatives?    

One would be the standard ham design -- a separate crystal for each 
band.   This has the great advantage of simplicity.   I need a crystal 
frequency for each band -- say six or seven if I don't cover all of 10.   
To use the oscillator I've just built, these would range from about 14 
to about 40 mcs.   These can be all third overtone and as special-
order crystals go, aren't terribly hard to get.   Seven by $15 or $20 is 
a little more money than I want to spend, but not totally impossible.   

I could redo the oscillator so as to be compatible with a crystal 
series I have (FT-101, maybe the KWM-2A), but I don't have any real 
spares and I don't particularly want to redo the oscillator. 

Thirdly, I could go to a synthesis approach.   For that, I may have 
crystals -- I have three or four junk ARC-27's that produced 1750 
100kcs channels 225-399.9 Mcs.   I also have some other UHF sets 
with similar output but probably somewhat different conversion 
schemes.   

(The ARC-27 was the UHF transceiver in the F-4H Phantom, the 
main Navy fighter of the Vietnam era and was used in other  high 
performance aircraft of that era.    It was heavy (around 40-50 
pounds) and very expen$ive.   A non-pressurized version (ARC-55) 
was used in large support aircraft and very different (lightweight) 
equipment was adapted or developed for rotating-wing aircraft.)  

The main crystal groups in the ARC-27 are 9.15 Mcs to 8.25 Mcs by 
0.1 Mcs steps (there's your 100 kcs channels) and 25.7-34.7 by 1 
Mcs.   Combining these (and an IF signal) they cover 20-29.9 Mcs by 
0.1 Mcs steps.   Then a multiple of 10 Mcs is added to get the final 
frequency.   I could use two of the 0.1 Mcs step crystals at 0.5 Mcs 
spacings, the ten 1 Mcs step crystals, and a 10 Mcs crystal to get 
about anything needed.   

This approach is more complex -- it requires combining three 
crystals to get each band.   Of course more crystal signals means 
much more potential for spurs.  If going that route, I'd be strongly 
tempted to change the concept to general coverage rather than ham 
bands only.  (And spurs are a certainty in a general coverage design -
- the goal is to minimize the strength and keep the worst out of 
critical bands.) 

In addition to combining three crystal frequencies, I might have to 
somewhat retune the VFO -- which for a general coverage design, I 
might be willing to do.  Of course with general coverage, the 
switching also becomes more complex.   Lacking a 60 position 
bandswitch, I'd have to use three switches -- 0.5 (2 positions), 1.0 
(10 positions), and 10 (3 positions) Mcs increments.   With some 
risk of confusing the operator the 0.5 and 10 Mcs switches could be 
combined -- but I'd probably get the hang eventually.

We're not just switching crystals there, either -- the front end and 
premixer output also must be tuned according to the band.   In a 
general coverage design, the number of front end bands rarely 
matches the number of crystal step bands and all that has to be 
figured out and made to work.   Typical front end bands might be 1.5-
4-8-16-30 Mcs -- a total of 4 bands -- note that those don't map 
neatly to the two or three switches for the crystals.   

In a general coverage design, the front end tuning cap has to be 
*large* and have a good ratio of max to minimum capacitance.   Then 
you get into Q problems at the high end of each range ... 

A larger chassis would be required.

Or -- third alternative -- I could probably design a hamband-only 
synthesis scheme from the beginning to use just two crystals at a 
time and probably not more than three or four, total.   The 1.75 Mcs 
crystal I already have would be one; reasonable multiples of that, 
added to one of maybe three other frequencies might do the trick and 
would not require retuning the VFO.   However this very likely keeps 
the awkward parts of the original scheme (problems covering 160 and 
10) without its seeming simplicity.

I'll probably doodle a while (particularly on the third choice) before 
deciding.   Told you this was going to take all winter.

Walt
KJ4KV





From hbr@mailman.qth.net  Sat Nov 29 17:41:58 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Sat, 29 Nov 2003 12:41:58 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 5
In-Reply-To: <3FC51DE1.21445.293DF8C@localhost>
References: <3FB93A90.5272.22A9C6E@localhost>
Message-ID: <3FC89416.19611.E7B23B@localhost>

We have a decision ...

I'm gonna try a general coverage design.   I have worked out a 
synthesis scheme using a series of crystals from the ARC-27 that 
should do the trick.  

The synthesizer:

1.  Add 7.55 or 8.05 Mcs (500 kcs steps -- that's the tuning range of 
the prototype VFO using 1U4's) to 24.7, 25.7, 26.7 ... 33.7 Mcs (1 
Mcs steps) to give 32.25 to 41.75 in 500 kcs steps.  Note that all 
desired products are above the 10 meter ham band and can be 
selected with a single bandpass filter.   The 24.7 ... crystals are 
overtone units and the ARC-27 uses a Butler oscillator; I will look at 
recycling the tuned circuit -- the oscillator, tuned circuit, crystal 
switch and socket are in one end of an assembly and it is 
conceivable that I could whack off that end.  But probably not -- there 
are other circuits similarly ganged and chances are the 'easy' way is 
to provide ten tuned circuits.   

(Slight possibility which will not be further discussed right now -- use 
the mixer and post mixer amp from this ARC-27 module too.   That 
would solve the mixer tuned circuit problems too ... although my 
problems are simpler than those of the ARC-27 because of the use of 
'sort of doubly balanced' mixers instead of conventional single ended 
ones and the narrower output tuning range.   Going this way I would 
have to wind some cam operated slug tuned coils ... gee, that ought 
to be fun.) 

The ARC-27 is a Collins set -- there's a slug rack, and jillions of 
gears drive this stuff.  Fewer cams than in the R-390 but a 
comparable number of gears, and in less space.
.
2. Subtract 20, 10, 0 Mcs.   This requires one oscillator which can be 
a pentode ECO with a choice of two tuned circuits in the plate.   This 
gives 12.25 to 41.75 Mcs in 500 kcs steps -- the sixty 500 kcs 
bands for full coverage of 0-30 Mcs.   One of three bandpass filters 
must be selected in the plate of this mixer to pick the right output 
frequency.

3.  Subtract the VFO -- 5.7 to 5.2 Mcs.   This gives 6.55 to 36.55 
Mcs which is 6.55 (the IF for which I have clock crystals to make a 
ladder filter) above 0-30 Mcs.   Doubly balanced mixer using a pair of 
6BN6's; output single ended and will be gang tuned with the receiver 
input circuits which are push-pull -- total of 5 gangs required on that 
capacitor.   

The details of the RF stage and synthesizer output tuning are 
undecided.   One way is to use a wide range tuning cap and cover 
several switch bands with one front end band -- say 1.5-3.5; 3.5-10; 
10-22; and 22-30 Mcs.   Fewer RF parts but the switching's very 
complicated; basically you have to build logic circuits through the 
two bandswitches and probably use relays to switch the coils.   And 
you get Q (hence gain) issues with such wide tuning ranges.   

The other way is individual 1 Mcs bands over the whole range.   
Small tuning cap, somewhat less switching logic (I think) but lots of 
parts -- say eight slug tuned coils and most of 30 (60 for RF stage) 
fixed capacitors per circuit.   The choice may be forced by the tuning 
cap --I'm not sure I can find a five gang wide range unit and if I do, it's 
apt to be a very large one.   (Update: no wide-range 5 gang in the 
archives.)   

Basically all this adds up to a 10-tube front end (eight for the 'local 
oscillator') with two bandswitches, a five-gang tuning cap, and a good 
double handful of coils.   It'll have to be built and tested on a separate 
chassis which can be mounted on or under the main receiver 
chassis.    

Well, maybe I can at least get the front end done this winter.   The 
VFO wasn't as hard as I thought ... maybe the same will be true of 
the synthesizer.

Walt
KJ4KV


From hbr@mailman.qth.net  Sun Nov 30 02:41:37 2003
From: hbr@mailman.qth.net (hbr@mailman.qth.net)
Date: Sat, 29 Nov 2003 21:41:37 -0500
Subject: [HBR] Yet Another HBR Project -- Chapter 6
In-Reply-To: <3FC89416.19611.E7B23B@localhost>
References: <3FC51DE1.21445.293DF8C@localhost>
Message-ID: <3FC91291.25837.2D5D7D8@localhost>

Maybe not that hard after all ... and very interesting.

Investigating the ARC-27 20-30 Mcs IF amplifier subassembly this 
morning I think there's a good chance that the synthesizer can be 
built there.   In addition to the crystal socket and switch (24.7 ... 33.7 
Mcs) the same shaft has a pair of cams which operate a slug rack 
with total of 8 slug tuned coils in four pairs.   One pair is in the plate 
of the Butler oscillator; that circuit and coils can be used unchanged 
except for retuning the coils slightly.  

(The reason for the retuning is that in the original the crystals run 
25.7 ... 34.7; I'm adding a new 24.7 at the bottom and removing the 
34.7 at the top, in order to improve the conversion scheme.)

A second pair of coils can be used in the plate of the 1st premixer -- 
the one that adds 7.55 or 8.05 Mcs.   The other two pairs can be 
switched in the plate of the 2nd premixer to subtract either 10 or 20 
Mcs.   The total range of frequencies is 12.25 to 41.75 Mcs so it 
shouldn't be hard to rewind coils that were designed to cover 20-30 
Mcs so they'll work.   Should it?   I mean, less than an octave either 
way ...

The switch has 14 positions in a full rotation, of which ten are used, 
corresponding to the ten crystals and the full range of the slug rack 
cams.  

There are two ways to go to control the thing.   It doesn't look too 
hard to extend the switch shaft in order to put a knob on it.   There's 
a gang that generates a four-bit code that could be used to switch 
front end coils on a per-Mc basis. There may or may not be enough 
friction to avoid having to make a detent.  Because of the strange 
number of switch positions, I can't just hook it to the shaft of a 
standard rotary switch.

The other route is using the autopositioner motor.   The code 
generating gang noted above feeds back the position, the motor 
makes it turn, and a slip clutch and pawl stop it when the code fed 
back matches the order.   Going this way I'd use a normal rotary 
switch to control the RF stage 1-Mcs steps and also generate the 
four-bit code for positioning of the synthesizer.   (Venn diagrams, 
anyone?   Now *there's* a rusty mental circuit!)   Conceptually clean, 
detenting is taken care of, and allows mounting the syn. anywhere I 
want, but the mechanical stuff -- gear alignment, rigidity, etc. -- could 
be messy and the motor/autopositioner assembly is heavy and 
bulky.   Do I want the receiver to go Rrrrrr-rrrrr--rrrrr ... CLACK each 
time I change the 1-Mc step?

A possible third way is to replace the 14-position switches with 
normal 12-position ones.   This may not work because of the need to 
operate the cams but in other respects it's appealing.

The rotary switch for the 10 Mcs and 0.5 Mcs increments will be off 
chassis; this will be marked 0 -- 0.5 -- 10 -- 10.5 -- 20 -- 20.5.  I may 
have to use a reed relay or two for switching on the chassis.   There 
are 7 tube sockets; 6 are 7 pin, which may be an issue -- though 
there's always the 6J6. There may or may not be room on the 
chassis for the three extra crystals -- 7.55, 8.05, and 10 Mcs.   

Anyhow, if I'm very lucky, except for the VFO everything up to the 
output to the signal mixer is going to wind up in one assembly for 
which someone else has done most of the mechanical work, 
including the most complicated rotary bandswitch and the tuned 
circuits.   It's a couple -- okay, a *few* -- months too early to 
celebrate, but I'm encouraged.

Walt
KJ4KV

From hbr@mailman.qth.net  Wed Nov 19 14:28:32 2003
From: hbr@mailman.qth.net (Kim Herron)
Date: Wed, 19 Nov 2003 09:28:32 -0500
Subject: [HBR] Re: GB> 1929-Style "QST SUPER 12" Receiver: UPDATE
In-Reply-To: <2563.198.208.159.14.1069249349.squirrel@webmail.durham.net
 >
Message-ID: <5.2.0.9.2.20031119092351.009f8ec0@mail.voyager.net>

Hi Gang,

      SNIP
>Well, to anyone complating the construction of a receiver like this
>utilizing ancient tubes---or ANY tubes, probably, for that matter---do not
>always suspect the worst when trouble-shooting...!
>
>The moral of the story is simply this: even if your tubes pass muster on a
>dynamic tube tester, it is NOT an accurate indication of how they'll
>perform "...in the field". Both of these old 224A's were NOISEY in their
>specific applications, for whatever reason(s)---and yet both had
>transconductance levels just in excess of 800 umhos.

      This is why the radio manufacturers always suggested substituting a 
known good tube,
or trying the tube in another radio that works.  Tubes testers are just 
that.  It's very difficult to
tell how the thing will work until it's in a circuit.  Testers give a good 
indication of tube condition
but can't be relied on for the final answer.  I keep a stock of about 500 
tubes that I KNOW work
because I've tried them in the various radios that I work on.  When 
possible, I test tubes that I've sold
the same way.  Even NEW tubes can be toast.


Thanks!!

Kim Herron
1-616-677-3706 


