From waltah at earthlink.net  Wed Oct  1 22:17:18 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Wed Oct  1 23:39:03 2008
Subject: [HBR] Another one-week (okay, probably not!) HBR -- Part 1
Message-ID: <000601c92436$2938ec00$7e01a8c0@waltah>

Pete said:

> How about some photos as the project progresses? You could open an
> account on PhotoBucket, and post the links as you progress with the
> project. Photos would be neat!!

I'll do photos when it gets a little farther.  As of this evening the
panel is done (except for whatever I forgot ...) and the chassis is
mostly laid out and centerpunched.

The Eddystone dial is just as much fun to install as I expected.  
Assembling it on the panel is a sort of four-hands-needed job.
However, it is a very good dial, AND good looking.

I discovered one design mistake: you can't really drive a dual
triode mixer with a triode LO in this way without getting a little bit
of pulling on the higher frequencies. I've been spoiled by doing it at
1700 kcs in dual conversion sets with a tunable second IF, but with
the LO going to 13 Mcs or something like that in this design, it
wouldn't work.  With a little jiggering of things I was able to switch
to a pentode ECO which will give enough isolation.

Might get the chassis holes done tomorrow.  I'll post some pics when
that's done.

> I'm playing around with the R-23 80kHz transformers. Boy, they don't
> appear to be very high Q, and use a high L to C ratio.  I assume this
> was done to control the bandwidth for AM reception? Also, I have a
> question about the button silver mica caps and the old dogbone style
> ceramic caps that were used.  I know these were good caps back in the
> late 30s and early 40s, but I wonder if it it would be good practice
> to replace them with newer 180pF dipped micas since these components
> are now 60 years old?

I seem to remember that there have been discussions of the Q of those
transformers before; maybe a couple of years ago.  You could try
searching the archives.  When you consider that they operate at 85kcs,
you wouldn't want a very high Q: Q=40 would give you a bandwidth of 2
kcs with one coil.

The ARC-5 manual has curves of the selectivity for the receivers, as I
recall. My previous HBR project with 4 85 kcs command set IFs is about
as sharp as you can use on an SSB signal with all the rods pulled up.
It's really too sharp to be ideal for AM reception, even by tuning to
one side -- when the voice signal is peaked, there's not enough
carrier to demodulate it properly.

As to replacing the caps inside the transformers, if they seem
okay, I don't think I'd bother. The MOLDED micas from those days are
bad actors because the bakelite shrinks due to heat and the passage of
time, pulls away from the leads (or cracks open) and moisture gets in,
but the ceramic and button silver micas are excellent quality; I don't
recall ever running into one that had failed unless there was obvious
mechanical damage.

Among the other command set parts, the sealed-in-the-can paper caps
are also fairly common failures, due to moisture getting in.  Most
sets need one of the bypass cans replaced.

Walt
KJ4KV




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From radioconnection at gmail.com  Sat Oct  4 14:35:45 2008
From: radioconnection at gmail.com (Peter Bertini)
Date: Sat Oct  4 14:47:37 2008
Subject: [HBR] IF transformers
In-Reply-To: <ccedf7ca0809301647t601b0d04gef6233330703cf88@mail.gmail.com>
References: <6900151.1222026307308.JavaMail.root@elwamui-little.atl.sa.earthlink.net>
	<ccedf7ca0809211828v7818dd0hb8fb6101c064bb7c@mail.gmail.com>
	<ccedf7ca0809281128h2cb922e4nc48fa16457c0f0af@mail.gmail.com>
	<ccedf7ca0809281138i71c88020w4a701b7339f517b2@mail.gmail.com>
	<6.2.1.2.2.20080928200814.03751d60@pop-server.nc.rr.com>
	<Pine.LNX.4.58.0809282107480.14799@arthur.atl.org>
	<ccedf7ca0809301647t601b0d04gef6233330703cf88@mail.gmail.com>
Message-ID: <ccedf7ca0810041135g43a7bb62of66f04e86a0ecdbd@mail.gmail.com>

Since I have several of these 85kc transformers to play with, I tried
two in cascade with good results. I tried several different coupling
cap values to couple the secondary of the 1st IFT to the primary of
the second one to see what effect the value would have on the
selectivity, and at what point the coupling became lossy.  Two in
cascade worked fine. I was curious, and added a third transformer, for
three in cascade. I ran into something odd: the two coils in the
middle IFT didn't seem to behave right; as if there was no mutual
coupling between them? This was even with the coils set for max.
coupling, close together. I don't understand what I am seeing. Adding
a small coupling cap from the high end of the primary to secondary LC
circuits in the second IFT solved the coupling problem.

Pete


On Tue, Sep 30, 2008 at 7:47 PM, Peter Bertini
<radioconnection@gmail.com> wrote:
> I'm playing around with the R-23 80kHz transformers. Boy, they don't
> appear to be very high Q, and use a high L to C ratio.  I assume this
> was done to control the bandwidth for AM reception? Also, I have a
> question about the button silver mica caps and the old dogbone style
> ceramic caps that were used.  I know these were good caps back in the
> late 30s and early 40s, but I wonder if it it would be good practice
> to replace them with newer 180pF dipped micas since these components
> are now 60 years old?
>
> Pete
>
> On Sun, Sep 28, 2008 at 9:11 PM, Bob <bob@atl.org> wrote:
>>
>> Harry Lythall - SM0VPO has some homebrew IF transformer
>> info under
>> reference: data technique: DIY IF cans
>>
>> http://web.telia.com/~u85920178/
>>
>> I should have photos of my HBR soon. It's got to go. No more room and if I
>> do well enough this semester to get into nursing school, no time for the
>> next few years.
>>
>> -Bob
>> AH7I Atlanta/Honolulu
>> ************************************
>> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
>> construction notes...... via http://www.qsl.net/k5bcq/
>> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>>
>>
>> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr
>>
>>
>
From daileyservices at qwest.net  Sat Oct  4 14:41:55 2008
From: daileyservices at qwest.net (TC Dailey)
Date: Sat Oct  4 14:53:38 2008
Subject: [HBR] HBR-13 for sale
Message-ID: <000b01c92650$e04b9a20$6502a8c0@w0eaj>

On QTH.COM, there's an HBR-13 for sale, with partial coil collection. (Eddystone Dial, too)

Look up WB1FRW, as he's the guy selling it.

Thought you guys would like to know it's out there.

Tom - W?EAJ

www.qrz.com/wb1frw
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From radioconnection at gmail.com  Sat Oct  4 15:32:24 2008
From: radioconnection at gmail.com (Peter Bertini)
Date: Sat Oct  4 15:44:15 2008
Subject: [HBR] HBR-13 for sale
In-Reply-To: <000b01c92650$e04b9a20$6502a8c0@w0eaj>
References: <000b01c92650$e04b9a20$6502a8c0@w0eaj>
Message-ID: <ccedf7ca0810041232y6f328492i21e8dc16a4b465f7@mail.gmail.com>

The real fun is hunting for the parts, coming up with some unique
improvements,  building it, making it work right, and putting it on
the air!!

I don't think I could enjoy buying one all made. No fun in that for me :(

Pete


On Sat, Oct 4, 2008 at 2:41 PM, TC Dailey <daileyservices@qwest.net> wrote:
> On QTH.COM, there's an HBR-13 for sale, with partial coil collection.
> (Eddystone Dial, too)
>
> Look up WB1FRW, as he's the guy selling it.
>
> Thought you guys would like to know it's out there.
>
> Tom - W?EAJ
>
> www.qrz.com/wb1frw
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via
> http://mailman.qth.net/mailman/listinfo/hbr
>
>
>
From daileyservices at qwest.net  Sat Oct  4 17:36:08 2008
From: daileyservices at qwest.net (TC Dailey)
Date: Sat Oct  4 17:47:51 2008
Subject: [HBR] HBR-13 for sale
References: <000b01c92650$e04b9a20$6502a8c0@w0eaj>
	<ccedf7ca0810041232y6f328492i21e8dc16a4b465f7@mail.gmail.com>
Message-ID: <007901c92669$36bb35b0$6502a8c0@w0eaj>

Yeah, I know... but it'd be a shame to have it go to somebody who didn't 
understand it's unique origins.

----- Original Message ----- 
From: "Peter Bertini" <radioconnection@gmail.com>
To: "HBR Receiver List" <hbr@mailman.qth.net>
Sent: Saturday, October 04, 2008 1:32 PM
Subject: Re: [HBR] HBR-13 for sale


> The real fun is hunting for the parts, coming up with some unique
> improvements,  building it, making it work right, and putting it on
> the air!!
>
> I don't think I could enjoy buying one all made. No fun in that for me :(
>
> Pete

From Hopperdhh at aol.com  Sun Oct  5 09:47:10 2008
From: Hopperdhh at aol.com (Hopperdhh@aol.com)
Date: Sun Oct  5 09:59:09 2008
Subject: [HBR] IF transformers
Message-ID: <cc8.3a300b1d.361a1f5e@aol.com>

Pete,

You can get into a situation where  the stray capacitive coupling can cancel 
the inductive coupling.  Maybe  that is what was happening.

Dan K9WEK


In a message dated  10/4/2008 2:36:21 P.M. Eastern Daylight Time, 
radioconnection@gmail.com  writes:
Since I have several of these 85kc transformers to play with, I  tried
two in cascade with good results. I tried several different  coupling
cap values to couple the secondary of the 1st IFT to the primary  of
the second one to see what effect the value would have on  the
selectivity, and at what point the coupling became lossy.  Two  in
cascade worked fine. I was curious, and added a third transformer,  for
three in cascade. I ran into something odd: the two coils in  the
middle IFT didn't seem to behave right; as if there was no  mutual
coupling between them? This was even with the coils set for  max.
coupling, close together. I don't understand what I am seeing.  Adding
a small coupling cap from the high end of the primary to secondary  LC
circuits in the second IFT solved the coupling problem.

Pete  




**************New MapQuest Local shows what's happening at your destination.  
Dining, Movies, Events, News & more. Try it out!      
(http://local.mapquest.com/?ncid=emlcntnew00000001)
From radioconnection at gmail.com  Sun Oct  5 10:42:55 2008
From: radioconnection at gmail.com (Peter Bertini)
Date: Sun Oct  5 10:54:52 2008
Subject: [HBR] IF transformers
In-Reply-To: <cc8.3a300b1d.361a1f5e@aol.com>
References: <cc8.3a300b1d.361a1f5e@aol.com>
Message-ID: <ccedf7ca0810050742y4179c1aci4688ba29b7c6507f@mail.gmail.com>

Could well be...  I didn't expect to see that.

 But I suspect going beyond two cascaded in the first stage would give
diminishing returns regardless.  I'll let the Q-Multiplier supply the
CW selectivity. KISS.

Pete


On Sun, Oct 5, 2008 at 9:47 AM,  <Hopperdhh@aol.com> wrote:
> Pete,
>
> You can get into a situation where  the stray capacitive coupling can cancel
> the inductive coupling.  Maybe  that is what was happening.
>
> Dan K9WEK
>
>
> In a message dated  10/4/2008 2:36:21 P.M. Eastern Daylight Time,
> radioconnection@gmail.com  writes:
> Since I have several of these 85kc transformers to play with, I  tried
> two in cascade with good results. I tried several different  coupling
> cap values to couple the secondary of the 1st IFT to the primary  of
> the second one to see what effect the value would have on  the
> selectivity, and at what point the coupling became lossy.  Two  in
> cascade worked fine. I was curious, and added a third transformer,  for
> three in cascade. I ran into something odd: the two coils in  the
> middle IFT didn't seem to behave right; as if there was no  mutual
> coupling between them? This was even with the coils set for  max.
> coupling, close together. I don't understand what I am seeing.  Adding
> a small coupling cap from the high end of the primary to secondary  LC
> circuits in the second IFT solved the coupling problem.
>
> Pete
>
>
>
>
> **************New MapQuest Local shows what's happening at your destination.
> Dining, Movies, Events, News & more. Try it out!
> (http://local.mapquest.com/?ncid=emlcntnew00000001)
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr
>
>
From waltah at earthlink.net  Wed Oct  8 14:12:34 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Wed Oct  8 15:27:00 2008
Subject: [HBR] Another one-week (okay, probably not!) HBR -- Part 2
Message-ID: <000701c92971$7580fa40$7e01a8c0@waltah>

The metalwork and the 'first mounting of parts' (as Heathkit would
say) are done. Pictures are at:

http://picasaweb.google.com/timbreblue/Walt#5254833299643465026
http://picasaweb.google.com/timbreblue/Walt#5254833820737451154
http://picasaweb.google.com/timbreblue/Walt#5254833430924088786
http://picasaweb.google.com/timbreblue/Walt#5254833472562276914
http://picasaweb.google.com/timbreblue/Walt#5254833653676698194

In the front view, the controls along the bottom are (L to R) BFO
tuning, ON/OFF switch, AUDIO GAIN, TUNING, and CAL (upper)/AGC
THRESHOLD (lower). The big hole on the left is for a 3" speaker and to
the right of the S-meter, switches for STDBY/OPERATE, BFO ON/OFF, and
CAL ON/OFF. Holes under the handles are for latches to hold the set in
the (to be built) cabinet.

Hinged top AND a drawer under ... now THAT will be a project.

The shield on top of the chassis is the upper half of a 3" x 4" x 5"
minibox.

>From the rear, the antenna coil is in the shield on the left, the RF
stage is the tube just to the right of there, and the mixer grid coil
is next toward the panel. The mixer is made up of the triode halves of
the two 19JN8's for which the pentode sections are the RF and
oscillator stages; the oscillator tube is behind the antenna coil in
the shield and behind that, the 1st IFT. There is a shield plate under
the chassis separating the antenna coil and RF stage from the
oscillator/mixer tube and mixer grid coil.

The oscillator coil is forward of the shield, next to the 1st IF
stage. The coil is sub-mounted to reduce heating from the chassis and
allow air flow around the coil -- there will be a way for air to come
in under the chassis. The two stages of IF run to the right from the
oscillator coil, ending at the 1st audio and plate detector tube. The
2nd audio and 3500 kcs marker oscillator stage is to the rear from the
detector tube. The 9-pin socket nearest the panel at the right is the
BFO and bias rectifier; the empty octal socket is for the 117Z6
rectifier.

The mounting of the dial and tuning capacitor is never easy but it is
especially tedious for the Eddystone 898 because exact alignment has
to be obtained with the capacitor mounted above the chassis. Laying
this out is a challenge. The shield holes on the chassis are slightly
elongated left/right to allow lateral adjustment; the holes in the
mounting ears on the tuning cap are elongated (by the mfr.) to permit
up/down tweaking.

The most obvious weakness of this layout is that the leads from the
oscillator tube to the coil are about 5" long. Long tuned circuit
leads are always an issue with plug in coil designs but I could have
done better by moving the first IFT out of the above-chassis shield
and moving the oscillator (and 1/2 mixer) tube closer to the coil.

It'll be a few days before there's anything else to report.

Peter said:
> I've been looking at the Star SR-700A receiver schematic

Thanks for that; I didn't know of this very refined design. I'll watch
for one on Ebay ... would be interesting to put one on the air!

Two striking features: The use of cascaded 55 kcs IF filter coils that
are detuned by switching capacitors in order to vary the selectivity
without moving the carrier edge of the passband. THAT is the way to do
adjustable selectivity if you're going to use a low IF to get narrow
bandpass; you could even apply it to use of the 85 kcs command set
IFTs.

(But the 'without moving the carrier edge' trick is only useful if you
also arrange for both LSB and USB to be LSB at this point; most
probably by switching the final local oscillator between above/below
the previous IF to select the sideband.)

And the Vackar local oscillator. While there is no magic 'stable
circuit,' the Vackar gives the best control over coupling between the
tube and tuned circuit of any of them, thus simplifying the job of
minimizing the effect of tube characteristics on output frequency when
using high gain (modern) tubes.

In a well-designed Vackar circuit at moderate frequencies, the only
drift you have to worry about is in the tank circuit parts: plugging
in a cold tube gives you the same frequency as the warmed-up one did.
So if the coil and capacitors are protected from temperature changes
and/or compensated, you get a very stable oscillator.

One improvement to the circuit shown is to tap the coil at the point
of zero RF voltage and feed the plate voltage through a resistor at
that point with no bypass cap. This eliminates the plate choke which
is effectively part of the tank circuit and thus a source of drift.

Push-pull oscillators also offer great advantages, starting with twice
the gain for the same (effective) tube capacitance.  However they're
best used with a push-pull mixer.

In the tickler feedback circuit of the W6TC designs, coupling to the
plate (actually, screen) circuit can be varied by adjusting the number
of turns and spacing of the plate coil, but the full grid capacitance
appears across the tank.

Using the screen of a pentode as the oscillator plate (as in the ECO
circuit) gives you a low gain oscillator tube anyhow, so the amount of
decoupling that can be done is probably quite limited. The ECO gives
up this advantage in exchange for the simplicity of a built-in buffer
and (in the W6TC designs) 2nd harmonic generator.

Since the major source of drift in these designs is likely to be the
plug-in coils, it's probably not worthwhile to spend a lot of time on
the oscillator circuit.  Good coils and a chassis layout that keeps
the oscillator coil as cool as possible are likely to be the most
useful focus.

Finally, I did find out why I can't post to this list using my regular
e-mail program. QTH.NET assumes that anyone using The BAT (my mailer)
is a spammer and rejects all such postings with a meaningless message.
I can post normally by using Outlook Express, or probably (with a bit
more work) by zapping the code that labels the mail files, as I'm sure
the serious spammers do.

Go figure.

Walt
KJ4KV



From merrijoy at comcast.net  Wed Oct  8 15:20:30 2008
From: merrijoy at comcast.net (Dave And Merrijoy)
Date: Wed Oct  8 15:32:44 2008
Subject: [HBR] Another one-week (okay, probably not!) HBR -- Part 2
References: <000701c92971$7580fa40$7e01a8c0@waltah>
Message-ID: <003301c9297a$ed9bcf10$7c88de62@davehdv6x9zkbd>

Walt, you are a craftsman, there is NO doubt!!
Dave w9ocm


----- Original Message ----- 
From: "Walt Hutchens" <waltah@earthlink.net>
To: <hbr@mailman.qth.net>
Sent: Wednesday, October 08, 2008 2:12 PM
Subject: Re[3]: [HBR] Another one-week (okay, probably not!) HBR -- Part 2


> The metalwork and the 'first mounting of parts' (as Heathkit would
> say) are done. Pictures are at:
>
> http://picasaweb.google.com/timbreblue/Walt#5254833299643465026
> http://picasaweb.google.com/timbreblue/Walt#5254833820737451154
> http://picasaweb.google.com/timbreblue/Walt#5254833430924088786
> http://picasaweb.google.com/timbreblue/Walt#5254833472562276914
> http://picasaweb.google.com/timbreblue/Walt#5254833653676698194
>
> In the front view, the controls along the bottom are (L to R) BFO
> tuning, ON/OFF switch, AUDIO GAIN, TUNING, and CAL (upper)/AGC
> THRESHOLD (lower). The big hole on the left is for a 3" speaker and to
> the right of the S-meter, switches for STDBY/OPERATE, BFO ON/OFF, and
> CAL ON/OFF. Holes under the handles are for latches to hold the set in
> the (to be built) cabinet.
>
> Hinged top AND a drawer under ... now THAT will be a project.
>
> The shield on top of the chassis is the upper half of a 3" x 4" x 5"
> minibox.
>
>>From the rear, the antenna coil is in the shield on the left, the RF
> stage is the tube just to the right of there, and the mixer grid coil
> is next toward the panel. The mixer is made up of the triode halves of
> the two 19JN8's for which the pentode sections are the RF and
> oscillator stages; the oscillator tube is behind the antenna coil in
> the shield and behind that, the 1st IFT. There is a shield plate under
> the chassis separating the antenna coil and RF stage from the
> oscillator/mixer tube and mixer grid coil.
>
> The oscillator coil is forward of the shield, next to the 1st IF
> stage. The coil is sub-mounted to reduce heating from the chassis and
> allow air flow around the coil -- there will be a way for air to come
> in under the chassis. The two stages of IF run to the right from the
> oscillator coil, ending at the 1st audio and plate detector tube. The
> 2nd audio and 3500 kcs marker oscillator stage is to the rear from the
> detector tube. The 9-pin socket nearest the panel at the right is the
> BFO and bias rectifier; the empty octal socket is for the 117Z6
> rectifier.
>
> The mounting of the dial and tuning capacitor is never easy but it is
> especially tedious for the Eddystone 898 because exact alignment has
> to be obtained with the capacitor mounted above the chassis. Laying
> this out is a challenge. The shield holes on the chassis are slightly
> elongated left/right to allow lateral adjustment; the holes in the
> mounting ears on the tuning cap are elongated (by the mfr.) to permit
> up/down tweaking.
>
> The most obvious weakness of this layout is that the leads from the
> oscillator tube to the coil are about 5" long. Long tuned circuit
> leads are always an issue with plug in coil designs but I could have
> done better by moving the first IFT out of the above-chassis shield
> and moving the oscillator (and 1/2 mixer) tube closer to the coil.
>
> It'll be a few days before there's anything else to report.
>
> Peter said:
>> I've been looking at the Star SR-700A receiver schematic
>
> Thanks for that; I didn't know of this very refined design. I'll watch
> for one on Ebay ... would be interesting to put one on the air!
>
> Two striking features: The use of cascaded 55 kcs IF filter coils that
> are detuned by switching capacitors in order to vary the selectivity
> without moving the carrier edge of the passband. THAT is the way to do
> adjustable selectivity if you're going to use a low IF to get narrow
> bandpass; you could even apply it to use of the 85 kcs command set
> IFTs.
>
> (But the 'without moving the carrier edge' trick is only useful if you
> also arrange for both LSB and USB to be LSB at this point; most
> probably by switching the final local oscillator between above/below
> the previous IF to select the sideband.)
>
> And the Vackar local oscillator. While there is no magic 'stable
> circuit,' the Vackar gives the best control over coupling between the
> tube and tuned circuit of any of them, thus simplifying the job of
> minimizing the effect of tube characteristics on output frequency when
> using high gain (modern) tubes.
>
> In a well-designed Vackar circuit at moderate frequencies, the only
> drift you have to worry about is in the tank circuit parts: plugging
> in a cold tube gives you the same frequency as the warmed-up one did.
> So if the coil and capacitors are protected from temperature changes
> and/or compensated, you get a very stable oscillator.
>
> One improvement to the circuit shown is to tap the coil at the point
> of zero RF voltage and feed the plate voltage through a resistor at
> that point with no bypass cap. This eliminates the plate choke which
> is effectively part of the tank circuit and thus a source of drift.
>
> Push-pull oscillators also offer great advantages, starting with twice
> the gain for the same (effective) tube capacitance.  However they're
> best used with a push-pull mixer.
>
> In the tickler feedback circuit of the W6TC designs, coupling to the
> plate (actually, screen) circuit can be varied by adjusting the number
> of turns and spacing of the plate coil, but the full grid capacitance
> appears across the tank.
>
> Using the screen of a pentode as the oscillator plate (as in the ECO
> circuit) gives you a low gain oscillator tube anyhow, so the amount of
> decoupling that can be done is probably quite limited. The ECO gives
> up this advantage in exchange for the simplicity of a built-in buffer
> and (in the W6TC designs) 2nd harmonic generator.
>
> Since the major source of drift in these designs is likely to be the
> plug-in coils, it's probably not worthwhile to spend a lot of time on
> the oscillator circuit.  Good coils and a chassis layout that keeps
> the oscillator coil as cool as possible are likely to be the most
> useful focus.
>
> Finally, I did find out why I can't post to this list using my regular
> e-mail program. QTH.NET assumes that anyone using The BAT (my mailer)
> is a spammer and rejects all such postings with a meaningless message.
> I can post normally by using Outlook Express, or probably (with a bit
> more work) by zapping the code that labels the mail files, as I'm sure
> the serious spammers do.
>
> Go figure.
>
> Walt
> KJ4KV
>
>
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via 
> http://mailman.qth.net/mailman/listinfo/hbr
>
>
>
> -- 
> No virus found in this incoming message.
> Checked by AVG.
> Version: 7.5.524 / Virus Database: 270.7.6/1714 - Release Date: 10/8/2008 
> 7:01 AM
>
> 

From jlandrigan at pol.net  Wed Oct  8 17:38:42 2008
From: jlandrigan at pol.net (jlandrigan@pol.net)
Date: Wed Oct  8 17:51:05 2008
Subject: [HBR] Re: HBR -- Part 2
Message-ID: <50280.10.250.10.1.1223501922.squirrel@webmail2.medscape.com>




Walt, 
This is really nice work. Did you use
a milling machine or layout, drill
and punch by hand with Greenlee punches?
After I get my permeability tuned
oscillator turned and milled I will be
tackling the HBR.
John KA4RXP


 
> On Wed, October 8,
2008 2:20 pm CDT,
Dave And Merrijoy wrote:
> 
> 
>
Walt, you are a craftsman, there is NO doubt!!
> Dave w9ocm
>

> 
> ----- Original Message -----
>
From:
"Walt
Hutchens"
> To:
> Sent: Wednesday, October 08,
2008 2:12 PM
> Subject: Re[3]: [HBR] Another one-week (okay, probably not!)
HBR -- Part 2
> 
> 
> > The metalwork and the 'first
mounting of parts'
(as Heathkit would
> > say) are done. Pictures
are at:
> >
> >
http://picasaweb.google.com/timbreblue/Walt#5254833299643465026
> >
http://picasaweb.google.com/timbreblue/Walt#5254833820737451154
> >
http://picasaweb.google.com/timbreblue/Walt#5254833430924088786
> >
http://picasaweb.google.com/timbreblue/Walt#5254833472562276914
> >
http://picasaweb.google.com/timbreblue/Walt#5254833653676698194
> >
> > In the front view, the controls along the bottom are (L
to R)
BFO
> > tuning, ON/OFF switch, AUDIO GAIN, TUNING, and CAL
(upper)/AGC
> > THRESHOLD (lower). The big hole on the left is for a
3" speaker and to
> > the right of the S-meter, switches for
STDBY/OPERATE, BFO ON/OFF, and
> > CAL ON/OFF. Holes under the
handles
are for latches to hold the set in
> > the (to be built)
cabinet.
> >
> > Hinged top AND a drawer under ... now THAT
will be a
project.
> >
> > The shield on top of the
chassis is the upper
half of a 3" x 4" x 5"
> >
minibox.
> >
> >>From the rear, the antenna coil is in the
shield on the left, the
RF
> > stage is the tube just to the right
of there, and the mixer grid
coil
> > is next toward the panel. The
mixer is made up of the triode
halves of
> > the two 19JN8's for
which the pentode sections are the RF
and
> > oscillator stages; the
oscillator tube is behind the antenna coil
in
> > the shield and
behind that, the 1st IFT. There is a shield plate
under
> > the
chassis separating the antenna coil and RF stage from
the
> >
oscillator/mixer tube and mixer grid coil.
> >
> > The
oscillator coil is forward of the shield, next to the 1st IF
> > stage.
The coil is sub-mounted to reduce heating from the chassis and
> > allow
air flow around the coil -- there will be a way for air to come
> > in
under the chassis. The two stages of IF run to the right from the
> >
oscillator coil, ending at the 1st audio and plate detector tube. The
> >
2nd audio and 3500 kcs marker oscillator stage is to the rear from
the
> > detector tube. The 9-pin socket nearest the panel at the right is
the
> > BFO and bias rectifier; the empty octal socket is for the
117Z6
> > rectifier.
> >
> > The mounting of
the
dial and tuning capacitor is never easy but it is
> > especially
tedious
for the Eddystone 898 because exact alignment has
> > to be
obtained with
the capacitor mounted above the chassis. Laying
> >
this out is a
challenge. The shield holes on the chassis are slightly
>
> elongated
left/right to allow lateral adjustment; the holes in the
> > mounting
ears on the tuning cap are elongated (by the mfr.) to
permit
> > up/down
tweaking.
> >
> > The most
obvious weakness of this layout is
that the leads from the
> >
oscillator tube to the coil are about 5"
long. Long tuned circuit
> > leads are always an issue with plug in coil
designs but I could
have
> > done better by moving the first IFT out of
the
above-chassis shield
> > and moving the oscillator (and 1/2 mixer)
tube closer to the coil.
> >
> > It'll be a few days
before
there's anything else to report.
> >
> > Peter
said:
>
>> I've been looking at the Star SR-700A receiver
schematic
> >
> > Thanks for that; I didn't know of this very
refined design. I'll
watch
> > for one on Ebay ... would be
interesting to put one on the
air!
> >
> > Two striking
features: The use of cascaded 55 kcs
IF filter coils that
> > are
detuned by switching capacitors in order to
vary the selectivity
> >
without moving the carrier edge of the passband.
THAT is the way to do
> > adjustable selectivity if you're going to use a
low IF to get
narrow
> > bandpass; you could even apply it to use of the
85 kcs
command set
> > IFTs.
> >
> > (But the
'without moving the carrier edge' trick is only useful if you
> >
also
arrange for both LSB and USB to be LSB at this point; most
> >
probably
by switching the final local oscillator between above/below
>
> the
previous IF to select the sideband.)
> >
> > And
the Vackar
local oscillator. While there is no magic 'stable
> >
circuit,' the
Vackar gives the best control over coupling between the
>
> tube and
tuned circuit of any of them, thus simplifying the job of
> > minimizing
the effect of tube characteristics on output frequency
when
> > using
high gain (modern) tubes.
> >
>
> In a well-designed Vackar
circuit at moderate frequencies, the only
> > drift you have to worry
about is in the tank circuit parts:
plugging
> > in a cold tube gives you
the same frequency as the
warmed-up one did.
> > So if the coil and
capacitors are protected
from temperature changes
> > and/or compensated,
you get a very
stable oscillator.
> >
> > One improvement to
the circuit
shown is to tap the coil at the point
> > of zero RF voltage
and
feed the plate voltage through a resistor at
> > that point with no
bypass cap. This eliminates the plate choke which
> > is effectively
part
of the tank circuit and thus a source of drift.
> >
>
>
Push-pull oscillators also offer great advantages, starting with twice
>
> the gain for the same (effective) tube capacitance.  However
they're
>
> best used with a push-pull mixer.
> >
> > In the tickler
feedback circuit of the W6TC designs, coupling to
the
> > plate
(actually, screen) circuit can be varied by adjusting
the number
> > of
turns and spacing of the plate coil, but the full
grid capacitance
> >
appears across the tank.
> >
> > Using the screen of a pentode
as the oscillator plate (as in the
ECO
> > circuit) gives you a low gain
oscillator tube anyhow, so the
amount of
> > decoupling that can be done
is probably quite limited.
The ECO gives
> > up this advantage in
exchange for the simplicity
of a built-in buffer
> > and (in the W6TC
designs) 2nd harmonic
generator.
> >
> > Since the major
source of drift in
these designs is likely to be the
> > plug-in coils,
it's probably
not worthwhile to spend a lot of time on
> > the oscillator
circuit.
 Good coils and a chassis layout that keeps
> > the oscillator
coil
as cool as possible are likely to be the most
> > useful focus.
>
>
> > Finally, I did find out why I can't post to this list
using
my regular
> > e-mail program. QTH.NET assumes that anyone using
The
BAT (my mailer)
> > is a spammer and rejects all such postings with a
meaningless message.
> > I can post normally by using Outlook Express,
or
probably (with a bit
> > more work) by zapping the code that
labels the
mail files, as I'm sure
> > the serious spammers do.
> >
> > Go figure.
> >
> > Walt
>
> KJ4KV
> >
> >
> >
> >
************************************
> > Visit the HBR Receiver Web
Site
with over 100 pictures of receivers and
> > construction
notes...... via
http://www.qsl.net/k5bcq/
> > there is also a mirror
(faster response)at
http://k5bcq.edebris.com/
> >
> >
> > Retrieve
reflector archived data via
> >
http://mailman.qth.net/mailman/listinfo/hbr
> >
> >
>
>
> > --
> > No virus found in this incoming
message.
> > Checked by AVG.
> > Version: 7.5.524 / Virus
Database:
270.7.6/1714 - Release Date: 10/8/2008
> > 7:01 AM
> >
> >
> 
>
************************************
>
Visit the HBR Receiver Web Site
with over 100 pictures of receivers and
>
construction notes...... via
http://www.qsl.net/k5bcq/
> there is also a
mirror (faster response)at
http://k5bcq.edebris.com/
> 
> 
>
Retrieve reflector
archived data via http://mailman.qth.net/mailman/listinfo/hbr
> 
>

> 
>

-------------- next part --------------
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From waltah at earthlink.net  Wed Oct  8 18:00:05 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Wed Oct  8 19:15:07 2008
Subject: [HBR] Re: HBR -- Part 2
Message-ID: <000701c92991$50dfa2c0$7e01a8c0@waltah>

John said:
> This is really nice work.

Thank you.  I've practiced a lot on projects that failed!

> Did you use a milling machine or layout, drill and punch by hand
> with Greenlee punches?

The most advanced tooling is a small drill press, but  most of the
holes were made with either a Skil electric drill with a 3/8" chuck or
a Stanley 'Handyman' hand drill from about 30 years ago. I have
Greenlee punches for the most common sizes of socket holes including
the 1" required for that meter. The speaker cut out and all the
rectangular holes were done with some combination of drilling a row of
holes, a Dremel with cutoff wheel, or a Sears electric saber saw
screwed to the middle of a sheet of plywood, blade up.

I actually like the little hand drill because you have such good control of
where that hole goes.  But when drilling 100 holes in a row, an electric
motor is a great help!

It's about 20 hours of metalwork, and another 10 or so of design and
layout.

I'll start the wiring tonight. That will take considerably longer.

> After I get my permeability tuned oscillator turned and milled I
> will be tackling the HBR.

We'll be watching for it!

Walt
KJ4KV


From daileyservices at qwest.net  Wed Oct  8 19:15:48 2008
From: daileyservices at qwest.net (TC Dailey)
Date: Wed Oct  8 19:27:46 2008
Subject: [HBR] Walt's creation
References: <000701c92991$50dfa2c0$7e01a8c0@waltah>
Message-ID: <001e01c9299b$cce66250$6402a8c0@w0eaj>

I'm impressed - somebody doing it the "old fashioned" way.  Many's the times 
when, in my youthful attempts to create yet another modern electronic 
wonder, my hands suffered the "death of a thousand cuts".  It's sort of a 
rite-of-passage I think - you know... spending hours, days, and weeks with 
now-permanent calluses at the base of my thumb-forefinger junction where the 
metal nibbler fit, just to make ALL those tube socket holes.

I salute you.  ('scuse me while I fetch another roll of gauze)

Tom - W?EAJ 

From waltah at earthlink.net  Sun Oct 12 06:09:54 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Sun Oct 12 07:24:58 2008
Subject: [HBR] Re: HBR -- Part 3
Message-ID: <000701c92c52$b12fa580$7e01a8c0@waltah>

Heathkit-terminology steps since last time:

Second mounting of parts -- output transformer, volume control, filter
choke, ON/OFF switch, speaker, and misc.
First wiring -- filaments and plate power supply
Second wiring -- 1st & 2nd Audio stages

Only made one mistake wiring the filaments this time! Pins 4 & 5 on 7
tube sockets; how, you wonder, could I get that wrong? Well ... I
wonder the same thing.

The audio section worked right away, though I had the interstage
coupling cap wrong, so had a bit too much hum. With that fixed, it is
silent at low to mid volume settings, only some hum at full volume.

The full volume hum comes from capacitive coupling between the chassis
(which is at power line ground voltage) and the neutral power wire
which is B- and the audio signal ground for all circuits.  This
voltage is of the order of one volt RMS and usually 'trashy.'  With a
750k volume control, just a few mmf of stray capacitance is enough to
produce an audible signal.

The audio detector has a much lower (than 750k) plate resistance; when
it's wired it will lower the impedance at this point, eliminating the
hum.

The audio stages have a high level of negative feedback and thus
relatively little gain -- I think a voltage gain of 3 from the volume
control to the voice coil.  But 100 mW of audio for a 4 ohm speaker is
about 0.65 volts RMS so with voltage gain 3, volume control set for
10% of max voltage gain, the detector output will only need to be
a bit over 2 volts and the 2nd IF output, in the milivolt range.

Sharp cutoff tubes are fine in an IF operating at that low level.  But
a sharp-cutoff tube in an RF stage is not ideal for ham band service.
Does anyone remember how unhappy Hallicrafters was when some people
substituted 6AK5's for the RF tube in one of their receivers?  Maybe
the HQ-129X?

This is not that bad, because the AGC voltages will be correct for the
tubes I'm using, but better front-end performance would result from
using 6EH7's in all three sockets. Then you'd have an 11 tube receiver
that might possibly be done as a 300 mA series string set ... a
different design!

'High fi' audio with frequency response shaped for communications
purposes makes signals a lot clearer and takes just a couple more
parts. Use of 1/2 of a 12AU7 for the audio output stage requires a
high efficiency speaker: the modern midget extended low frequency
response speakers used for computer and car audio will not deliver
enough volume.  Speakers from taxi and CB sets are fine.

Most of the circuitry of this set is copied from the earlier band
imaging set with six tubes, push-pull oscillator and mixer, 80/40
meters.  So I THINK all the problems with 'transformerless' power
supply have been resolved.  Yeah, that's what I think ...

I plan to wire the audio and AGC plate detector circuits next. These
are respectively the triode halves of the 19JN8 1st audio and 2nd IF
stages.

Following that, I'll wire the local oscillator, so I can start working
on the oscillator coil while wiring the other stages.

The Eddystone dial that I have is factory-calibrated for six ham
bands; I think it came as part of a kit of parts for the G3LOK
receiver design. (Think: HBR with bandswitching, using itty-bitty
coils ... NOT a great design!) And I'm using the tuning cap that came
with.

This dial is a nice (silk screen?) printing job on painted metal and
the scales are very close to linear so it makes sense to try to track
the oscillator to the dial, rather than recalibrating.  However this
sort of thing requires a bit of cut-and-try ... probably a week's
work, on and off, to get a decent result.

This will require a three-point fit. Typically the three parts to be
adjusted would be the coil inductance, the shunt (trimmer) capacitor,
and a capacitor in series with the tuning cap, called the padder
capacitor. These would adjust the low and high ends and the midband
point, respectively. The W6TC designs use a tap on the coil rather
than a series padder cap, probably because tapping the coil is cheaper
than another high quality capacitor. However, moving a tap to get
midpoint dial tracking right is tough.

On the other hand, changing a capacitor down inside a coil form with
an APC trimmer in the top may not be simpler ... I'll probably try
using the tap, first.  I bought 10' of PVC for $2.39 plus tax, and I
have a bunch of rusty octal tubes ...

Just one more thought: that capacitor tracked that dial with the coils
that are in that (busted up) front end assembly. Maybe my first effort
should be to duplicate the in-set coils and copy the oscillator
circuit parts. Hummm ...

The tube lineup has turned out to be surprisingly tidy:

19JN8 -- RF & 1/2 mixer
19JN8 -- ECO LO & 1/2 mixer

This looks messy, but the RF drives one half of the mixer and the LO
drives the other, thus each pentode is coupled to the triode in the
same envelope.  The two triode plates and cathodes are joined; the
plates go to the 1st IFT.

19JN8 -- 1st IF & AGC clamp (triode is diode-connected)
19JN8 -- 2nd IF & AGC plate detector
19JN8 -- 1st audio & audio plate detector
12AU7 -- 2nd audio & 3.5 Mcs marker oscillator
12AT7 -- BFO & bias rectifier (2nd triode is diode-connected)

117Z6 -- Plate supply rectifier

There's also a 150 mA 9-pin miniature with a triode and two diodes
with independent cathodes that could be substituted for the 12AT7 if
another diode is needed. The 14GT8 was designed for use in combination
ratio-detector/1st audio service in AC/DC AM/FM receivers.

Another report in another few days ...

Walt
KJ4KV



From radioconnection at gmail.com  Sun Oct 12 13:17:55 2008
From: radioconnection at gmail.com (Peter Bertini)
Date: Sun Oct 12 13:30:38 2008
Subject: [HBR] Re: HBR -- Part 3
In-Reply-To: <000701c92c52$b12fa580$7e01a8c0@waltah>
References: <000701c92c52$b12fa580$7e01a8c0@waltah>
Message-ID: <ccedf7ca0810121017g5d1ff236ge761d04acdf2734e@mail.gmail.com>

Are those green sockets Western Electrics?  Your layout looks very
tidy. We're all awaiting more updates!
Peter


On Sun, Oct 12, 2008 at 6:09 AM, Walt Hutchens <waltah@earthlink.net> wrote:
> Heathkit-terminology steps since last time:
>
> Second mounting of parts -- output transformer, volume control, filter
> choke, ON/OFF switch, speaker, and misc.
> First wiring -- filaments and plate power supply
> Second wiring -- 1st & 2nd Audio stages
>
> Only made one mistake wiring the filaments this time! Pins 4 & 5 on 7
> tube sockets; how, you wonder, could I get that wrong? Well ... I
> wonder the same thing.
>
> The audio section worked right away, though I had the interstage
> coupling cap wrong, so had a bit too much hum. With that fixed, it is
> silent at low to mid volume settings, only some hum at full volume.
>
> The full volume hum comes from capacitive coupling between the chassis
> (which is at power line ground voltage) and the neutral power wire
> which is B- and the audio signal ground for all circuits.  This
> voltage is of the order of one volt RMS and usually 'trashy.'  With a
> 750k volume control, just a few mmf of stray capacitance is enough to
> produce an audible signal.
>
> The audio detector has a much lower (than 750k) plate resistance; when
> it's wired it will lower the impedance at this point, eliminating the
> hum.
>
> The audio stages have a high level of negative feedback and thus
> relatively little gain -- I think a voltage gain of 3 from the volume
> control to the voice coil.  But 100 mW of audio for a 4 ohm speaker is
> about 0.65 volts RMS so with voltage gain 3, volume control set for
> 10% of max voltage gain, the detector output will only need to be
> a bit over 2 volts and the 2nd IF output, in the milivolt range.
>
> Sharp cutoff tubes are fine in an IF operating at that low level.  But
> a sharp-cutoff tube in an RF stage is not ideal for ham band service.
> Does anyone remember how unhappy Hallicrafters was when some people
> substituted 6AK5's for the RF tube in one of their receivers?  Maybe
> the HQ-129X?
>
> This is not that bad, because the AGC voltages will be correct for the
> tubes I'm using, but better front-end performance would result from
> using 6EH7's in all three sockets. Then you'd have an 11 tube receiver
> that might possibly be done as a 300 mA series string set ... a
> different design!
>
> 'High fi' audio with frequency response shaped for communications
> purposes makes signals a lot clearer and takes just a couple more
> parts. Use of 1/2 of a 12AU7 for the audio output stage requires a
> high efficiency speaker: the modern midget extended low frequency
> response speakers used for computer and car audio will not deliver
> enough volume.  Speakers from taxi and CB sets are fine.
>
> Most of the circuitry of this set is copied from the earlier band
> imaging set with six tubes, push-pull oscillator and mixer, 80/40
> meters.  So I THINK all the problems with 'transformerless' power
> supply have been resolved.  Yeah, that's what I think ...
>
> I plan to wire the audio and AGC plate detector circuits next. These
> are respectively the triode halves of the 19JN8 1st audio and 2nd IF
> stages.
>
> Following that, I'll wire the local oscillator, so I can start working
> on the oscillator coil while wiring the other stages.
>
> The Eddystone dial that I have is factory-calibrated for six ham
> bands; I think it came as part of a kit of parts for the G3LOK
> receiver design. (Think: HBR with bandswitching, using itty-bitty
> coils ... NOT a great design!) And I'm using the tuning cap that came
> with.
>
> This dial is a nice (silk screen?) printing job on painted metal and
> the scales are very close to linear so it makes sense to try to track
> the oscillator to the dial, rather than recalibrating.  However this
> sort of thing requires a bit of cut-and-try ... probably a week's
> work, on and off, to get a decent result.
>
> This will require a three-point fit. Typically the three parts to be
> adjusted would be the coil inductance, the shunt (trimmer) capacitor,
> and a capacitor in series with the tuning cap, called the padder
> capacitor. These would adjust the low and high ends and the midband
> point, respectively. The W6TC designs use a tap on the coil rather
> than a series padder cap, probably because tapping the coil is cheaper
> than another high quality capacitor. However, moving a tap to get
> midpoint dial tracking right is tough.
>
> On the other hand, changing a capacitor down inside a coil form with
> an APC trimmer in the top may not be simpler ... I'll probably try
> using the tap, first.  I bought 10' of PVC for $2.39 plus tax, and I
> have a bunch of rusty octal tubes ...
>
> Just one more thought: that capacitor tracked that dial with the coils
> that are in that (busted up) front end assembly. Maybe my first effort
> should be to duplicate the in-set coils and copy the oscillator
> circuit parts. Hummm ...
>
> The tube lineup has turned out to be surprisingly tidy:
>
> 19JN8 -- RF & 1/2 mixer
> 19JN8 -- ECO LO & 1/2 mixer
>
> This looks messy, but the RF drives one half of the mixer and the LO
> drives the other, thus each pentode is coupled to the triode in the
> same envelope.  The two triode plates and cathodes are joined; the
> plates go to the 1st IFT.
>
> 19JN8 -- 1st IF & AGC clamp (triode is diode-connected)
> 19JN8 -- 2nd IF & AGC plate detector
> 19JN8 -- 1st audio & audio plate detector
> 12AU7 -- 2nd audio & 3.5 Mcs marker oscillator
> 12AT7 -- BFO & bias rectifier (2nd triode is diode-connected)
>
> 117Z6 -- Plate supply rectifier
>
> There's also a 150 mA 9-pin miniature with a triode and two diodes
> with independent cathodes that could be substituted for the 12AT7 if
> another diode is needed. The 14GT8 was designed for use in combination
> ratio-detector/1st audio service in AC/DC AM/FM receivers.
>
> Another report in another few days ...
>
> Walt
> KJ4KV
>
>
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr
>
>
From merrijoy at comcast.net  Sun Oct 12 13:36:25 2008
From: merrijoy at comcast.net (Dave And Merrijoy)
Date: Sun Oct 12 13:49:06 2008
Subject: [HBR] Re: HBR -- Part 3
References: <000701c92c52$b12fa580$7e01a8c0@waltah>
	<ccedf7ca0810121017g5d1ff236ge761d04acdf2734e@mail.gmail.com>
Message-ID: <004101c92c91$0db70cb0$7c88de62@davehdv6x9zkbd>

This all reminds me of Walt's receiver and transmitter that he built and 
wrote about in the pages
of the early issues of Electric Radio.  Well thought out - well written - 
and well built.  It is sure good
to see you writing and building again, Walt.
Dave w9ocm


----- Original Message ----- 
From: "Peter Bertini" <radioconnection@gmail.com>
To: "HBR Receiver List" <hbr@mailman.qth.net>
Sent: Sunday, October 12, 2008 1:17 PM
Subject: Re: Re[2]: [HBR] Re: HBR -- Part 3


> Are those green sockets Western Electrics?  Your layout looks very
> tidy. We're all awaiting more updates!
> Peter
>
>
> On Sun, Oct 12, 2008 at 6:09 AM, Walt Hutchens <waltah@earthlink.net> 
> wrote:
>> Heathkit-terminology steps since last time:
>>
>> Second mounting of parts -- output transformer, volume control, filter
>> choke, ON/OFF switch, speaker, and misc.
>> First wiring -- filaments and plate power supply
>> Second wiring -- 1st & 2nd Audio stages
>>
>> Only made one mistake wiring the filaments this time! Pins 4 & 5 on 7
>> tube sockets; how, you wonder, could I get that wrong? Well ... I
>> wonder the same thing.
>>
>> The audio section worked right away, though I had the interstage
>> coupling cap wrong, so had a bit too much hum. With that fixed, it is
>> silent at low to mid volume settings, only some hum at full volume.
>>
>> The full volume hum comes from capacitive coupling between the chassis
>> (which is at power line ground voltage) and the neutral power wire
>> which is B- and the audio signal ground for all circuits.  This
>> voltage is of the order of one volt RMS and usually 'trashy.'  With a
>> 750k volume control, just a few mmf of stray capacitance is enough to
>> produce an audible signal.
>>
>> The audio detector has a much lower (than 750k) plate resistance; when
>> it's wired it will lower the impedance at this point, eliminating the
>> hum.
>>
>> The audio stages have a high level of negative feedback and thus
>> relatively little gain -- I think a voltage gain of 3 from the volume
>> control to the voice coil.  But 100 mW of audio for a 4 ohm speaker is
>> about 0.65 volts RMS so with voltage gain 3, volume control set for
>> 10% of max voltage gain, the detector output will only need to be
>> a bit over 2 volts and the 2nd IF output, in the milivolt range.
>>
>> Sharp cutoff tubes are fine in an IF operating at that low level.  But
>> a sharp-cutoff tube in an RF stage is not ideal for ham band service.
>> Does anyone remember how unhappy Hallicrafters was when some people
>> substituted 6AK5's for the RF tube in one of their receivers?  Maybe
>> the HQ-129X?
>>
>> This is not that bad, because the AGC voltages will be correct for the
>> tubes I'm using, but better front-end performance would result from
>> using 6EH7's in all three sockets. Then you'd have an 11 tube receiver
>> that might possibly be done as a 300 mA series string set ... a
>> different design!
>>
>> 'High fi' audio with frequency response shaped for communications
>> purposes makes signals a lot clearer and takes just a couple more
>> parts. Use of 1/2 of a 12AU7 for the audio output stage requires a
>> high efficiency speaker: the modern midget extended low frequency
>> response speakers used for computer and car audio will not deliver
>> enough volume.  Speakers from taxi and CB sets are fine.
>>
>> Most of the circuitry of this set is copied from the earlier band
>> imaging set with six tubes, push-pull oscillator and mixer, 80/40
>> meters.  So I THINK all the problems with 'transformerless' power
>> supply have been resolved.  Yeah, that's what I think ...
>>
>> I plan to wire the audio and AGC plate detector circuits next. These
>> are respectively the triode halves of the 19JN8 1st audio and 2nd IF
>> stages.
>>
>> Following that, I'll wire the local oscillator, so I can start working
>> on the oscillator coil while wiring the other stages.
>>
>> The Eddystone dial that I have is factory-calibrated for six ham
>> bands; I think it came as part of a kit of parts for the G3LOK
>> receiver design. (Think: HBR with bandswitching, using itty-bitty
>> coils ... NOT a great design!) And I'm using the tuning cap that came
>> with.
>>
>> This dial is a nice (silk screen?) printing job on painted metal and
>> the scales are very close to linear so it makes sense to try to track
>> the oscillator to the dial, rather than recalibrating.  However this
>> sort of thing requires a bit of cut-and-try ... probably a week's
>> work, on and off, to get a decent result.
>>
>> This will require a three-point fit. Typically the three parts to be
>> adjusted would be the coil inductance, the shunt (trimmer) capacitor,
>> and a capacitor in series with the tuning cap, called the padder
>> capacitor. These would adjust the low and high ends and the midband
>> point, respectively. The W6TC designs use a tap on the coil rather
>> than a series padder cap, probably because tapping the coil is cheaper
>> than another high quality capacitor. However, moving a tap to get
>> midpoint dial tracking right is tough.
>>
>> On the other hand, changing a capacitor down inside a coil form with
>> an APC trimmer in the top may not be simpler ... I'll probably try
>> using the tap, first.  I bought 10' of PVC for $2.39 plus tax, and I
>> have a bunch of rusty octal tubes ...
>>
>> Just one more thought: that capacitor tracked that dial with the coils
>> that are in that (busted up) front end assembly. Maybe my first effort
>> should be to duplicate the in-set coils and copy the oscillator
>> circuit parts. Hummm ...
>>
>> The tube lineup has turned out to be surprisingly tidy:
>>
>> 19JN8 -- RF & 1/2 mixer
>> 19JN8 -- ECO LO & 1/2 mixer
>>
>> This looks messy, but the RF drives one half of the mixer and the LO
>> drives the other, thus each pentode is coupled to the triode in the
>> same envelope.  The two triode plates and cathodes are joined; the
>> plates go to the 1st IFT.
>>
>> 19JN8 -- 1st IF & AGC clamp (triode is diode-connected)
>> 19JN8 -- 2nd IF & AGC plate detector
>> 19JN8 -- 1st audio & audio plate detector
>> 12AU7 -- 2nd audio & 3.5 Mcs marker oscillator
>> 12AT7 -- BFO & bias rectifier (2nd triode is diode-connected)
>>
>> 117Z6 -- Plate supply rectifier
>>
>> There's also a 150 mA 9-pin miniature with a triode and two diodes
>> with independent cathodes that could be substituted for the 12AT7 if
>> another diode is needed. The 14GT8 was designed for use in combination
>> ratio-detector/1st audio service in AC/DC AM/FM receivers.
>>
>> Another report in another few days ...
>>
>> Walt
>> KJ4KV
>>
>>
>>
>> ************************************
>> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
>> construction notes...... via http://www.qsl.net/k5bcq/
>> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>>
>>
>> Retrieve reflector archived data via 
>> http://mailman.qth.net/mailman/listinfo/hbr
>>
>>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via 
> http://mailman.qth.net/mailman/listinfo/hbr
>
>
>
> -- 
> No virus found in this incoming message.
> Checked by AVG.
> Version: 7.5.524 / Virus Database: 270.8.0/1720 - Release Date: 10/11/2008 
> 3:59 PM
>
> 

From waltah at earthlink.net  Sun Oct 12 19:33:36 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Sun Oct 12 20:48:52 2008
Subject: [HBR] Re: HBR -- Part 3 (PART ONE)
Message-ID: <000e01c92cc2$fb136680$7e01a8c0@waltah>

I am again unable to send to the list owing to being considered a spammer.
I'll try a binary search, hoping to find the offending section.  There are
no real instructions for this, just 'the text of your message seems to have
words or punctuation that makes it look like spam.'

Sorry for the extra messages.

Quoting self:
> The Eddystone dial that I have is factory-calibrated for six ham
> bands; I think it came as part of a kit of parts for the G3LOK
> receiver design. (Think: HBR with bandswitching, using itty-bitty
> coils; NOT a great design!) And I'm using the tuning cap that
> came with.

Oops! Not G3LOK, but G3RKK, a later, fairly similar design that is
described in considerable detail in the RSGB 'Radio Communications
Handbook,' Fourth Edition, 2nd printing, 1969. (Good book for serious
HBR-ers to have, BTW) The commercial 'Electroniques Ltd.' front end
for this receiver is described there, including a circuit diagram that
matches the equipment I have.

One might wonder why I didn't just use this bandswitching front end
assembly: The reason (aside from wanting to do a plug in coil design)
is that it's pretty close to junk, with wires loose, plastic parts and
wires that have had close encounters of the 100-watt soldering iron
kind, and a few parts broken or missing. And except for what appears
to be an excellent tuning cap, it's a 'budget' design, all the way.

After a bit of study it looks like the 80M and/or 160M oscillator
coils may be gone, rewound with who knows what for some higher
frequency. Anyway, the windings on one of them are loose.

The good news is that I have the circuit diagram and (I think) most of
the actual parts that allowed that oscillator to match that dial. It
is a Vackar circuit, which has the virtue of using a very simple coil.

(END OF PART ONE)

From waltah at earthlink.net  Sun Oct 12 20:02:52 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Sun Oct 12 21:19:06 2008
Subject: [HBR] Re: HBR -- Part 3 (PART TWO.TWO
Message-ID: <001f01c92cc7$355d70c0$7e01a8c0@waltah>

BEGINNING OF PART TWO.TWO

Part two failed to go through, so it has been split into two parts.  This is
the second.

It should be possible to get a very good start on tracking by just
matching the inductance of the new plug-in coil to the one in the
Electroniques front end for those bands that have the coils intact. If
the caps that are still there are also matched, it should be very
close on the bands that have all parts and just a one or two variable
problem on the others. Unfortunately, I want to start with 80M, and
I'm pretty sure that coil has been trashed.

On the whole, all this seems pretty good but there are likely to be
some challenges.

I spent a couple of hours today diagramming the working set with the
detector circuit I want to use. (Follows the Tempo ONE) Lots of parts
there.

Walt
KJ4KV

(END OF PART TWO.TWO)


From waltah at earthlink.net  Sun Oct 12 20:16:35 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Sun Oct 12 21:32:35 2008
Subject: [HBR] Re: HBR -- Part 3 (PART TWO.ONE.ONE)
Message-ID: <002e01c92cc9$15abd080$7e01a8c0@waltah>

(BEGINNING OF PART TWO.ONE.ONE)

Part two.one failed to go through, so it has been split into two parts.
This is
the first.

Unfortunately the tube they used is a 6AJ8, the 9 pin miniature
version of the 6K8 triode-heptode. So there's no way to use the same
tube for the oscillator, even if I wanted to. I am going to try to use
the W6TC ECO scheme. Because different tubes have different electron
transit times, they produce different phase shifts and you get
different tracking, particularly in high frequency wide band circuits.
However, this is NOT a wide band design; that issue should be minor.

END OF PART TWO.ONE.ONE

From waltah at earthlink.net  Sun Oct 12 21:00:43 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Sun Oct 12 22:15:51 2008
Subject: [HBR] Re: HBR -- Part 3 (FINAL)
Message-ID: <001701c92ccf$22be0260$7e01a8c0@waltah>

We're down to one paragraph that I have reduced to simple sentences with no
punctuation other than periods at the end of each sentence.  It has to do
with some oscillator issues.  The only thing I can imagine is that there's
some word or phrase in that paragraph that makes my post look like spam.

It doesn't seem worth pursuing this any further.

Windy, I've no idea how you put up with this.  Sharyn and I run a couple
dozen lists totalling over 7000 members.  We would be gone in two minutes
(okay maybe two days) if they treated members this way.  Can you or anyone
suggest another list, similar content (and membership) that doesn't use
QTH.NET?  Offlist replies, please.

Walt
KJ4KV



From radioconnection at gmail.com  Mon Oct 13 18:18:49 2008
From: radioconnection at gmail.com (Peter Bertini)
Date: Mon Oct 13 18:31:38 2008
Subject: [HBR] Re: HBR -- Part 3 (FINAL)
In-Reply-To: <001701c92ccf$22be0260$7e01a8c0@waltah>
References: <001701c92ccf$22be0260$7e01a8c0@waltah>
Message-ID: <ccedf7ca0810131518r5640057av56e92b10c10e4a2f@mail.gmail.com>

Walt

Maybe you could create a free Gmail account and post to HBR from
there. Gmail works fine for me.

Pete

On Sun, Oct 12, 2008 at 9:00 PM, Walt Hutchens <waltah@earthlink.net> wrote:
> We're down to one paragraph that I have reduced to simple sentences with no
> punctuation other than periods at the end of each sentence.  It has to do
> with some oscillator issues.  The only thing I can imagine is that there's
> some word or phrase in that paragraph that makes my post look like spam.
>
> It doesn't seem worth pursuing this any further.
>
> Windy, I've no idea how you put up with this.  Sharyn and I run a couple
> dozen lists totalling over 7000 members.  We would be gone in two minutes
> (okay maybe two days) if they treated members this way.  Can you or anyone
> suggest another list, similar content (and membership) that doesn't use
> QTH.NET?  Offlist replies, please.
>
> Walt
> KJ4KV
>
>
>
> ************************************
> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
> construction notes...... via http://www.qsl.net/k5bcq/
> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>
>
> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr
>
>
From waltah at earthlink.net  Wed Oct 15 12:40:26 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Wed Oct 15 13:56:16 2008
Subject: [HBR] Re: HBR -- Part 4
Message-ID: <000e01c92ee4$cb0e4120$7e01a8c0@waltah>

In part 3, the two audio stages got wired and working and I figured
out that the parts set from which the Eddystone dial and tuning cap
that I'm using came, had a Vackar local oscillator.

The audio stages have essentially no hum.

Yesterday I wired the audio detector -- a plate detector using the
triode half of the 1st audio 19JN8. At full volume there was enough
hum to be audible in the next room.

I fixed one obvious wiring mistake by moving this tube to the next to
lowest voltage point on the series filament string. That definitely
improved things. Then I did what I should have done first: replaced
that tube. Bingo! Hum all gone. Although the tube was 'new,' it had
excessive heater-cathode leakage. It may be satisfactory in
another stage.

One of the issues in designing with series filaments is that the
higher the voltage between the filament and cathode, the more leakage
current there will be. This usually isn't a problem if the cathode is
at signal ground for that stage, but there are a few stages in this
design for which that's not true. The audio plate detector is one of them:
for SSB and CW the BFO is coupled to the cathode and any AC current
flowing between the filament and cathode will also be injected there.

Interestingly (at least if your interests are a bit warped!) the local
oscillator stage has the same issue, even though the cathode is
bypassed to ground. That's because the LO circuit is so sensitive to
disturbance that even having heater-cathode leakage shunting the lead
from the cathode inside the tube to the point where it is (RF)
grounded to the tuning cap frame causes a significant change in tube
characteristics. In most oscillator circuits there will be enough
change to cause a few CPS FM on the oscillator, when operating on the
higher bands. This will be noticed as a warble when receiving CW and
as distortion on SSB voice signals.

Because of this issue the LO stage has to be at the cold end of the
series string and when the tube has two sections with filaments in
series (as in the 19JN8) the oscillator section should be the cold
one.

The Vackar circuit allows full control of coupling between the tube
and tank circuit, but because the ECO circuit doesn't have a very high
oscillator gain, I doubt that very much decoupling will be possible.
However, this is an issue that W6TC dealt with -- it's a major reason
a high Q oscillator coil and high-C design were chosen. It may be
okay.

(The higher the tank Q, the less is the effect of a change in tube
characteristics.)

The tickler feedback oscillator of the W6TC designs allows control of
coupling at the plate, but the tank itself is straight across the
grid.

A better design would use a high-gain separate triode oscillator --
one of the UHF TV oscillator triodes like the 6CW4 (Nuvistor) would
probably be excellent. Best of all, of course, is a crystal controlled
1st converter to a much lower tunable IF as used in advanced
communications receivers of the 1960's: crystals have Q's in the
thousands, so significant changes in tube characteristics are
tolerable.  But of course these would be more complicated designs.

When the set was switched on, the 117Z6 rectifier would flash one of
the two filament sections to near white brilliance.  NOT GOOD for the
life of the tube. Since our line voltage is around 122, I stuck a 100
ohm 1 watt metal film resistor in series: that reduced the problem by
half AND equalized the brilliance of the two halves.  Still not
great, but certainly much better.

With the resistor the (hot) filament voltage is reduced to 114. Plenty
high enough.

The only thing I can figure is that the strands of filament that
actually touch the cathode sleeve don't heat up as quickly and thus
stay at low resistance longer, leaving the center strands to absorb
most of the voltage and overheat, until the cathode sleeve begins to
get hot. Any difference at all between the two (series) filaments
would cause the same to occur in one section relative to the other. By
limiting the inrush current (the cold resistance of the tube is about
245 ohms) the series resistor slows the heating enough to allow better
equalization.

This problem is probably much more serious with some makes of tubes
than others but I only have two and they're of the same make.

Because the mechanics of posting with a mailer that isn't the one I
normally use are time consuming I'd rather write fewer longer posts.
However, since I also have trouble with getting tagged as spam for
content (the binary search and multiple posts of the other night) I'll
try to post each day that something actually gets done.

Hopefully that was a one-time event.

Next: The AGC circuits and winding of the 3rd IFT.

Walt
KJ4KV




From waltah at earthlink.net  Fri Oct 17 12:38:42 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Fri Oct 17 13:54:54 2008
Subject: [HBR] Re: HBR -- Part 5
Message-ID: <000701c93076$e3269300$7e01a8c0@waltah>

The AGC plate detector is wired and seems to be working. That included
the two controls (back panel for AGC delay and front for AGC
bias/threshold, effectively an RF/IF gain control) and the bias supply. This
circuit has a BUNCH of parts; I'm glad it's done.

Rather than use a voltage divider on the bias output to get down to
around -50 to -70 volts for the AGC detector cathode, I hooked the
diode-connected triode bias rectifier to the filament of the same
tube, letting the filament string serve as the voltage divider. Seems
to work fine, minimizes heater-cathode voltage, and with the filaments
arranged properly, delivers the right bias.

With the detectors seeming to be okay, the next thing was winding the
3rd IFT. I have some shielded single-slug tuned coils with four base
pins that were used in the 1.5-2.0 Mcs range, so they were ideal --
but they had only one winding. The 3rd IF to detector transition
corresponds to the switch from IF signals that reference chassis
ground to audio signals referencing the common buss; by far the
easiest way to do that is with a transformer. Primary signal ground is
the chassis, secondary signal ground is the common buss: What could be
easier?

Also the secondary must be center tapped to provide signals of both
polarities so the BFO signal can be cancelled out at the grid of the
AGC detector.  Yep, Yaesu (makers of the Tempo ONE) had smart people
even in the 60's -- I'd never have figured this circuit out for
myself!

Anyway I stripped off the single winding and replaced it with 100
turns of #40, an experience I'm not looking forward to repeating for
the other two transformers. It can be done, though -- in this case,
after breaking the wire halfway through on the first two tries. Two
300 mmf caps in series give a center tap and it tunes about 1.5-1.9
Mcs in the can. It wasn't quite pure luck: I stuck one of the caps on
the original winding (looked like about 50 turns of #34 or so) and
dipped that, to guide my guesswork.

Over that winding a layer of paper and on top of that, 30 turns of #30
as a primary. Everything stuck together with clear nail polish. Should
work ...

I expect about 50 or 60 turns of #30 scramble-wound in a pile would
also have worked, although there wouldn't be much room for the primary
if it were done that way. The two windings must either be insulated
from each other or spaced because the primary is at plate voltage.

With the transformer installed and the output side of the 2nd IF stage
wired, I stuck a temporary grid resistor to ground, draped a clip lead
antenna over my GDO coil and got a 'thump' as it tuned past the IF.
A DVM attached to the AGC output showed a peak to several volts.  I
stuck one of the filter crystals in a test oscillator, draped the clip
lead antenna over that, and peaked the coil at the correct frequency.

It's silent, either with or without a carrier signal, meaning no
mistakes in grounding (that would pick up the trash between chassis
ground and the power line common) ... yet. Everything is working so
far!

Today I hope to wire up the LO and start figuring out that problem --
particularly getting it to track the dial. In periods of frustration
I'll wind the next IF transformer and do the 1st IF and S-meter circuits
-- the S-meter is driven by a bridge circuit from the cathode (voltage
drops on signals) and screen grid (voltage increases ...) of the 1st
IF stage.

That S-meter circuit is another item stolen from the Tempo ONE.  It
avoids the need for a separate S-meter amplifier tube as used by W6TC.
However I think the circuit I'm using pretty much requires a 200 or
100 uA meter and W6TC's will work with a (then cheaper) 1 mA movement.

Walt
KJ4KV

From waltah at earthlink.net  Thu Oct 23 05:09:30 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Thu Oct 23 08:13:23 2008
Subject: [HBR] Re: HBR -- Part 6
Message-ID: <000701c934ef$13a9e820$7e01a8c0@waltah>

The local oscillator is wired and the 80M (3500-4000 kcs) band
oscillator coil wound and tracking the dial. This was a BUNCH of work,
but seems to be successful.

The oscillator is a Vackar, although not a great one, due mainly to
the small value of the tuning cap. The really good Vackars for the 5
Mcs range swamp both grid and plate with 100s-1000s of mmf caps; this
one has 100 mmf on the grid and 126 mmf on the screen grid (=plate)

But standard Vackar circuits for this frequency range use tuning caps
in the 50 mmf range; mine is a 15 mmf delta-C unit as commonly chosen
for the W6TC and similar ham-band-only designs. Using such a small cap
and with the lower gain of an ECO, you can't use an extremely high-C
circuit.

The coil goes from the screen grid to a capacitive voltage divider.
The tap of the divider goes to the control grid. A fixed cap ('padder
cap') goes from screen to ground. The tuning cap goes from the control
grid end of the coil to ground and is paralleled by an air variable
glued in the top of the coil ('trimmer cap') and a very small air
variable on the panel, for calibration trimming purposes.

In traditional ham work a two point fit to the dial calibration is
generally used.  A trimmer cap that's across the tuning cap is used to
set the top end of the band to something like 95 (on an 0-100 dial
scale) and the coil is adjusted to put the bottom end at 5 or so on
the scale.  Then a stable frequency source or frequency counter is
used to mark the dial for in-between frequencies.

However my Eddystone 898 is already calibrated for the G3RKK-design
receiver. It's a nice, professional calibration job for six bands,
160-10 meters, and nearly perfectly linear. I'm using the tuning cap
that came with the dial in this set. Rather than recalibrate the thing
(when I could not do nearly so nice a job) the plan is to fit the
receiver tuning to the scales that are already there. Getting an
accurate match requires a three point fit.

The typical three point scheme uses the fact that changing the coil
inductance moves all frequencies by the same percentage, the
(parallel) trimmer mainly moves the top end of the dial, and the
(series) padder mainly moves the bottom end. While you can calculate
the values for a scale for which you have precise percentage numbers
-- there are programs on the web to do it for a linear scale and cap
-- fitting to a not-perfectly-linear scale on an existing dial with a
cap that isn't straight-line-capacitance is a trial-and-error process.

The best approach depends on how the various adjustments are done. In
this case I wanted to select a fixed value of padder cap, making that
the hardest variable to change. So I started with a wild guess about
the padder (several times the max value of the tuning cap plus trimmer
is a good start) and used the trimmer and inductance value (removing
and/or spacing turns on the coil) to get the end points right.

With the ends right, I checked the mid point. With the first try, the
mid point was 8 kcs low in frequency: when the dial was set for an
oscillator frequency of 5450 kcs (3750 + 1700 kcs IF) the actual
frequency was 5442 kcs. Over several hours of work I increased the
padder cap (mainly lowering the low end frequency), corrected the low
end by decreasing the inductance, and brought the high end back down
by increasing the trimmer value. Because the tuning range is small
(500 kcs at over 5 Mcs -- less than 10%) the adjustments interact a
lot, so you have to overshoot each adjustment at first and go back and
forth many times.

Reducing the coil from the initial 30 turns to 26 and increasing the
padder from 100 to 126 mmf (measured value of cap marked 120 mmf) and the
trimmer from 2 mmf to about 10 mmf did the job.

The W6TC coil designs are beautiful to look at and very practical for
use but they're impossible to work with for a cut and try design. I
did the initial work with the chassis upside down and the coil form
(no base plug) and other parts tacked to the tube and coil sockets.
Only when I had the padder (fixed) value right did I assemble the
padder, the air trimmer, and the coil form onto the tube base. The
APC-25 trimmer is glued in the top of the coil with PVC pipe cement;
the coil is epoxied to the salvaged base from a metal octal tube.

A two point fit will do for the final tweak (when everything is wired
up) bringing the mid point error to less than 1 kcs. That is about the
width of the lines on the frequency dial and rather less than the
draftsman's errors in placing a couple of them.

Yeah, making the coil fit the dial calibration is kind of a ship in
the bottle exercise. And I get to do it again, for five more bands.
When I get all done, I'll be able to say whoopee, I got the ship in
the bottle.

The good news is that the results from 80 will be some help with (can
be roughly scaled to) the other bands and since 80 is the widest band
(percentagewise) the fit won't be as critical, anyway.

As assembled it drifted down about three kcs during well over an hour
of warm-up. Fairly standard for a 5.2-5.7 Mcs oscillator and this type
of construction. I replaced the Western Electric socket (with those
oh-so-convenient extra terminals) with a socket mounted on spacers
about 3/16" above the chassis. The socket pins stick down just far
enough that you can wire them in the usual way and there's ample space
for air to flow up around the pins, taking heat from them and the
socket along.

With this arrangement, not only is less heat transferred to the
chassis, but in about 3/4 hour, the drift nearly stops, showing that
the tube temperature has stabilized. This result is logical, because
the hotter the tube (base, socket, pins, wiring ...) the greater the
air flow. This process reaches equilibrium much faster (at a lower
temp) than the one in which heat is dissipated only from the tube
envelope and by conduction into the chassis and wiring.

LO (and VFO) tubes generally should NOT be shielded: not only do most
tube shields make the tube run hotter, but more of the heat will be
conducted back into the chassis.  When a tube will not be shielded, it
should NOT have a shield base socket, since that alone significantly
increases the temperature and heat transfer to the chassis.

With the drift this low and so well-behaved, the right temperature
compensating caps on the tube socket and either the coil socket or
tuning cap should easily get it to the 100 cps/hour range on the lower
bands.

There's no need for a three point fit for the RF and antenna coils.
With the maximum coil Q being around 150, being within a few kcs
across the band is plenty good enough. A two point fit at (say) 10%
and 90% of the dial will do.

I'll post new pictures in a day or so.

Plate voltage is often fed to Vackar oscillators through a choke or
resistor to the plate. That's an error: the resistor loads the coil
(there's RF voltage there, right?) and the choke is another reactance
in the oscillator circuit, hence another source of instability.
Feeding through a resistor at a tap near the zero RF voltage point
eliminates both issues, giving the highest possible coil Q, hence best
possible rejection of frequency change due to voltage fluctuations and
tube characteristic changes. There is no bypass cap at this point --
it floats.

The tap is twisted and soldered into the length of wire at the right
point, then the two ends are fed through two holes from the inside of
the coil so the loop is inside. The coil is wound both ways from the
tap. The resistor is thus part of the coil assembly.

I'll probably do the 2nd IFT and 1st IF stage next.  Ugh ... another
100 turns of #40 wire ...

Walt
KJ4KV

From waltah at earthlink.net  Wed Oct 29 14:18:37 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Wed Oct 29 14:23:18 2008
Subject: [HBR] HBR -- Part 7
Message-ID: <000701c939fb$2a7a4340$7e01a8c0@waltah>

Here are the pictures with the oscillator coil and wiring. They're
more interesting if you click the 'magnify' button at the upper right:

http://picasaweb.google.com/timbreblue/Walt#5261666031775899570

You can see the raised mounting of the oscillator tube. It's the one
to the right of the shield, next to the empty IF transformer hole.

http://picasaweb.google.com/timbreblue/Walt#5261666323291227186

The allen wrench in the Fahnstock clip is for the shaft couplings and
knobs.  The tuning cap shaft extension is a rusty piece of scrap I had
on hand; I'll find something better, eventually.

http://picasaweb.google.com/timbreblue/Walt#5261666451689928738

The oscillator socket is the ceramic 9 pin miniature toward the lower
left.  The dabs of masking tape all over the place hold the wiring
in place as I go along; when finished I'll lace it.

The 1st IF and S-meter circuits are wired. It picks up the signal from
my GDO and the S-meter deflects, so all that is working.  There's a
trace of hum (at full volume) on the (pure) signal from the GDO so
that will have to be looked into.  Most likely, heater-cathode
leakage, probably in the plate detector stage.  Second choice,
inadequate filtering of some high voltage.

One definite problem is that there's an offset of about -0.7V on the
AGC line, evidently coming from the vacuum diode I used in this
circuit. "Shucks, I should have thought of that." There are some
options for dealing with this; I don't know which I'll try first.

The next construction step will be the crystal filter, 1st IFT, and
mixer circuit.

And a question: Does anyone have recommendations for securing of turns
on the coils?  Particularly on PVC-pipe coils?  I know that one should
do the bare minimum, because when I've coated the whole coil in the
past I got a lot more distributed capacitance and it was DRIFTY.
First, of all, it drifted steadily for a few weeks while the coating
dried, then it drifted excessively with each heating/cooling cycle, 
compared to a bare coil.

Since I'm using fairly heavy wire -- #22, roughly -- I am able to wind
these coils very tightly and that does help, but maybe a few dabs of
PVC pipe cement on each end? Plus where the gap is, near the tap? Maybe 
thin the usual cement a bit and just use dabs?  Or ????

Walt
KJ4KV

From daileyservices at qwest.net  Wed Oct 29 23:56:01 2008
From: daileyservices at qwest.net (TC Dailey)
Date: Wed Oct 29 23:57:25 2008
Subject: [HBR] HBR -- Part 7
References: <000701c939fb$2a7a4340$7e01a8c0@waltah>
Message-ID: <00c501c93a4b$ce918010$6402a8c0@w0eaj>

downright beautiful, Walt.

That old-trick with the allen in the Fahnstock was found on the SP-600, the 
TCS series, and many other receivers.  Hey, you can ALWAYS find it! 
(providing somebody puts it back where they found it, of course) 

From waltah at earthlink.net  Fri Oct 31 18:52:38 2008
From: waltah at earthlink.net (Walt Hutchens)
Date: Fri Oct 31 18:57:39 2008
Subject: [HBR] HBR -- Part 8
Message-ID: <000701c93bb3$c6841720$7e01a8c0@waltah>

> There's a trace of hum (at full volume) on the (pure) signal from
> the GDO so that will have to be looked into. Most likely,
> heater-cathode leakage, probably in the plate detector stage. Second
> choice, inadequate filtering of some high voltage.

The first guess was the winner: Heater-cathode leakage in the plate
detector stage.  Remember when the best high-fi amps applied a few
volts positive bias to the heaters?  That's what they were fixing.

The 50-watt amp in the last RCA Tube Manual has this circuit.  You can
do the same thing (if no simpler approach works) by returning the
cathode to a negative supply.  This voltage must be a few volts
greater than the peak filament voltage.

The cathode sleeve acts as a plate for a diode having the filament as
a cathode. When the heater swings negative relative to the sleeve some
electrons reach the cathode and flow in the cathode circuit. This
effect is unimportant in most circuits (any time the cathode is
grounded for signal AND 60 cps frequencies) but in high gain circuits
with a 'hot' cathode, it must be reckoned with.

The plate detector cathode is where the BFO is injected for SSB, but
I've found that I can ground it for 60 CPS through a small choke and
0.1 mfd cap; that eliminates the hum on a strong carrier.  Also it is 
grounded when on AM anyway.  

> One definite problem is that there's an offset of about -0.7V on the
> AGC line, evidently coming from the vacuum diode I used in this
> circuit. "Shucks, I should have thought of that." There are some
> options for dealing with this; I don't know which I'll try first.

The reason for this is that even with no voltage applied to the diode,
there are some electrons striking the plate, hence some negative
current flowing in the external circuit having a resistance of a bit
over a megohm.  One microamp would give one volt ...

This turns out to have a very neat solution: Reduce the cathode
resistors so that the cathode bias is about +0.3 volts, giving a total
grid bias with zero signal of about 1 volt, as desired for the 19JN8
pentode.

I've seen a commercial-grade receiver that had no cathode resistors at
all: they used the AGC to do the whole job. No protection for the
tubes that way, though, if the AGC fails.

> The next construction step will be the crystal filter, 1st IFT, and
> mixer circuit.

Starting with 100 turns of #40 on a 1/4" diameter slug-tuned form.
Ugh. However, this time I didn't break it the first couple of times.

Testing of the two IF stages showed three more problems:

1. With a modulated signal, the audio amp was driven into distortion
before the AGC kicked in. I ran into the same issue with the earlier
receivers using this (plate detector) AGC circuit and the solution is
to tap the last IFT so that the voltage going to the AGC is
considerably higher than that going to the audio detector. I switched
from two 300 mmf caps in series across the IFT output winding, to a
200/620 mmf combination giving about a 3:1 ratio and that makes things
a LOT better.

2. When the AGC bias control (RF/IF gain control) is reduced, you can
hear hum, which goes away as you continue to reduce the gain.  That
seems likely to be a bypassing problem around the diode; I haven't
looked into that yet.

3. The 3rd IFT didn't peak up correctly on the AGC voltage when I put
a signal through from the 1st IFT. This turned out to be a bad
coupling cap from the 3rd IFT to the grid of the AGC detector.

Of course 'turned out to be ...' was after substituting tubes and
removing and disassembling the IFT, looking for a short or something.
There's probably a rule that every worthwhile project will include at
least one bad part.

That's a corollary to the rule that some items in your junkbox are
junk.

The gain of the IF/detector chain may be a bit low. I'll worry about
that later on, if necessary. There's plenty more AF gain available,
and since that's set by a feedback resistor, it's very easy to change
if needed.  And there are some things to check in the IF stages.  The
voltages are in the ballpark, but the plate current of the tubes is
low; I think the screen voltage is a few volts below what it should
be.  Also the tubes might be sub-par; while they're claimed to be new,
I haven't checked them.

I probably don't even have data for 19JN8s for my TV-7. However the
data can be figured out by looking for single section tubes equivalent
to the respective halves.

Testing is easier, now that the S-meter is working.

The half-lattice crystal filter is in and working.  Using crystals
that are 1.5 kcs apart in frequency, the nose is reasonably flat and
about 2.2 kcs wide.

Next steps are wiring the mixer and winding the front end coils.  I'm
thinking that I will use the W6TC method of bandspreading these,
namely, tapping the tuning cap down on the coil.  I have a cap meeting
the HBR specs (delta C = 15 mmf) so there's no reason that I can't
just wind the front end coils using the original HBR specs.

Walt
KJ4KV


