[Hallicrafters] Hallicrafters SX-71
Bill Collins
n0rry at swbell.net
Thu Feb 14 22:22:39 EST 2008
It's good to see some reference made to the sx-71. I have two that I have
been working on for a while. The first one I bought from an estate of an
SK, and he had been working on the 2nd converter--I had no idea of what he
had actually done or why, so started looking for a parts rig, found one at a
hamfest, took it home and it actually worked a little. Well, My parts rig
changed into a "let's fix this one too" rig. I rebuilt the 2nd converter
assembly, found a couple of resistors burnt in two, replaced them, recapped
both radios, and now that I have gone back to work (after 5 months of
disability), I don't have time to pursue them anymore (I need to retire,
no?) I am pretty sure that all they need now is just realignment, so I am
looking forward to that, but don't have any experience doing such. I have
an old but stable Heathkit signal generator (recapped and checked, tools,
manual, a sams photofact, and no time. Dang it. So one of these days, I
will be whining for help on this project. I really enjoy all the info
provided by the members-lots of good reading, and I even absorb some of it!
haha. If anyone has any tips or pointers on the SX-71, I will be all
ears. I took lots of digital pictures along the way while I was operating
on the 2nd converter especially.
Anyway, thanks for the info that you all share.
Bill
N zero R R and a Y
----- Original Message -----
From: <hallicrafters-request at mailman.qth.net>
To: <hallicrafters at mailman.qth.net>
Sent: Thursday, February 14, 2008 3:00 AM
Subject: Hallicrafters Digest, Vol 49, Issue 20
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Today's Topics:
1. (no subject) (Bill)
2. SX-71 serial # and Run # markings (Chuck McGregor)
3. Re: Re: [Boatanchors] Replacing recttubeswithdiodesquestion
(jeremy-ca)
4. Re: SX-71 serial # and Run # markings (W4AWM at aol.com)
5. Re: Replacing 6H6 with diodes. (Kenneth G. Gordon)
----------------------------------------------------------------------
Message: 1
Date: Wed, 13 Feb 2008 19:53:32 -0500
From: "Bill" <kirklandb at sympatico.ca>
Subject: [Hallicrafters] (no subject)
To: <hallicrafters at mailman.qth.net>
Message-ID: <002201c86ea4$09b1d380$1401a8c0 at bill1qh4y921ze>
Content-Type: text/plain; charset="us-ascii"
Yes, I am in a pissy mode. My humble apologies.
I meant to ask to ask for the previous email to be passed along.
Now to the basement with a beer.
------------------------------
Message: 2
Date: Wed, 13 Feb 2008 17:59:26 -0800
From: Chuck McGregor <cbmcg at comcast.net>
Subject: [Hallicrafters] SX-71 serial # and Run # markings
To: hallicrafters at mailman.qth.net
Message-ID: <20080214020553.EC50F8582AD at mailman.qth.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed
Sorry to ask a seemingly silly question, but where should I expect to
find the serial number and the run number stamp on an
SX-71 ? They're not on the chassis top or the rear apron, and
there's nothing on the inside of the chassis side panels (where the
SX-42 run # hides). I find three inspection stamps on the chassis
underside, below the 2nd converter subchassis. I haven't pulled the
front panel to see if any numbers are hidden behind it.
Thanks & 73
Chuck N7RHU
------------------------------
Message: 3
Date: Wed, 13 Feb 2008 22:17:22 -0500
From: "jeremy-ca" <km1h at jeremy.mv.com>
Subject: Re: [Hallicrafters] Re: [Boatanchors] Replacing
recttubeswithdiodesquestion
To: "Bill" <kirklandb at sympatico.ca>
Cc: boatanchors at mailman.qth.net, hallicrafters at mailman.qth.net
Message-ID: <02f201c86eb8$1f4ff230$6500a8c0 at KITTYMA123>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Bill, it took me quite awhile to quit laughing, you should do well in a
stand up comedy club!
Engineering tradeoffs, phase noise, IP3 and AC/DC all in the same breath! On
a 60-70 year old entry level radio no less which was the start of this
thread! I could see it if the SX-115 was being discussed but a S-40B? Wow,
what a stretch!
If you wish to discuss those engineering performance subjects and my
involvement with Ulrich Rhode, Kenwood and Yaesu I will be glad to discuss
it on the proper forum. The Hallicrafters or Boatanchors forum is not the
place for it.
Carl
KM1H
----- Original Message -----
From: "Bill" <kirklandb at sympatico.ca>
To: "'jeremy-ca'" <km1h at jeremy.mv.com>; <wq9e at dtnspeed.net>;
<erastber at tampabay.rr.com>
Cc: <boatanchors at mailman.qth.net>; <hallicrafters at mailman.qth.net>
Sent: Wednesday, February 13, 2008 6:52 PM
Subject: RE: [Hallicrafters] Re: [Boatanchors] Replacing
recttubeswithdiodesquestion
> Unfortunately Carl I don't seem to have a copy of an earlier email from
> you
> discussing any exceptions or voltage reduction. I only saw the email I
> responsed to
> which made quite blunt general statements. What I've found lacking in
> your responses
> Carl is a lack of discussion of the engineering trade offs or a good
> solid analytical
> analysis. Please pass it along.
>
> e.g. Just because something is done, in one receiver, e.g. AC/DC radios
> where
> B+ is applied, doesn't mean it was the best thing to do. They may well
> have made an engineering trade off, cost, performance, simplicity of
> design for the
> sake of some tube life. Who knows, maybe it was intentional, keeps the
> customer buying
> tubes.
>
> As for National giving the ok, great but since I don't have access to
> the engineering
> report I have no idea what the trade offs are.
>
> As for receiver sensitivity, good to hear that it didn't change but what
> other parameters
> have to measured, e.g. IP3, oscillator phase noise?
>
> Instead of indicating such and such is a myth because "it worked for
> me/others", I would
> rather see a good solid engineering/analytical discussion.
>
> It's good to have a great RF lab, unfortunately you didn't quote any
> measured results.
> Maybe in a previous email thread? If not, posting them and maybe some
> enterprising
> individual could put it up in an html page. Reminds me, guess I should
> do a google.
>
> I merely pointed out the obvious differences between the tube rectifier
> and the solid
> state rectifier. If you have some good analytical data, I would love to
> see it and then
> perhaps a good html page could be set up.
>
> I guess in summary there are 4 groups, "best practices", "acceptable
> practices", "bad practices"
> and anything else. It seems some of those that methods that might be
> considered "best (better)practices"
> get relegated to myth status.
>
>
------------------------------
Message: 4
Date: Wed, 13 Feb 2008 23:34:10 EST
From: W4AWM at aol.com
Subject: Re: [Hallicrafters] SX-71 serial # and Run # markings
To: cbmcg at comcast.net
Cc: hallicrafters at mailman.qth.net
Message-ID: <cef.2a1d7fce.34e51ec2 at aol.com>
Content-Type: text/plain; charset="US-ASCII"
Hi Chuck,
The serial numbers on most Hallicrafters receivers of that vintage were on
paper tags glud to the rear chassis banel. Unfortunately, many have not
passed
the test of time and rough handling. Normally the run numbers are stamped on
top of the chassis. If you don't see the run number, I could consider it to
be a
first series.
73,
John, W4AWM
**************
The year's hottest artists on the red carpet at the
Grammy Awards. Go to AOL Music.
(http://music.aol.com/grammys?NCID=aolcmp00300000002565)
------------------------------
Message: 5
Date: Wed, 13 Feb 2008 22:59:11 -0800
From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
Subject: [Hallicrafters] Re: Replacing 6H6 with diodes.
To: Hallicrafters at mailman.qth.net
Message-ID: <47B3763F.31712.DCB085 at localhost>
Content-Type: text/plain; charset=US-ASCII
On 14 Feb 2008 at 9:59, Rodney Bunt wrote:
> Not only high back resistance you need VERY low forward junction
> voltage. A tube diode conducts in the forward direction from a VERY
> low voltage. A diode if silicon needs approx 0.7v forward bias before
> it conducts, a Germanium (1N34) needs 0.3volt forward bias. Today you
> could use Shotkey diodes, but the 6H6 uses very little power and works
> very well.
Yes.
> An old trick is to reduce the filament voltage, thereby
> reducing the "electron cloud" around the cathode (these -ve electrons
> tend to repel other electrons from leaving the cathode) reducing the
> filament voltage, reduces the "cloud" reducing the forward bias
> voltage necessary to conduct.
>
> Rodney
> VK2KTZ
Thanks for the tip, Rodney. And you're absolutely correct. I
can't see any good reason to change a 6H6 for a pair of SS
diodes. The SS diodes won't do as good a job, and there
really isn't much of a savings. The 6H6 is very reliable.
When I changed the 6H6 in my Scott SLR-F back in the
1960s, it REALLY didn't help. In fact, the change made it
work worse. I took it out.
Thanks for the info.
Ken Gordon W7EKB
------------------------------
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