[Hallicrafters] More SX99 questions

Thu Feb 5 08:37:41 EST 2009

Both the Halli and National circuits will benefit from more BFO 
injection resulting in substantially more audio recovery and less of a 
need to ride the RF gain. It will take a bit of experimenting but Ive 
found around 50 pf to my liking for CW/SSB.

Both models will substantially benefit from a bit of zener regulation of 
the HFO and BFO;  5W zeners are about. .25 each these days

It would be interesting to have a S-20R and S-40 (S-85, SX-99, etc) to 
make changes and comparisons. The S-20R uses the gimmick on the diode 
detector.

Carl
KM1H

----- Original Message ----- 
From: "Mark Drakage" <markdd at nc.rr.com>
To: "N8IE" <n8ie at woh.rr.com>
Cc: "'ANTHONY CASORSO'" <canthony15 at msn.com>; 
<hallicrafters at mailman.qth.net>; "'rbethman'" <rbethman at comcast.net>
Sent: Wednesday, February 04, 2009 11:05 PM
Subject: Re: [Hallicrafters] More SX99 questions

Hi, there should be a wire coming from pin 1 on T2 to pin 4 of V4. The
gimmick wire coming from pin 3 of V5 is typically wrapped around the T2
pin 1/ pin V4 wire at least one turn. Of course the gimmick wire needs
to be insulated where it wraps around the other wire. Each turn produces
about 1-2 pf capacitance. One turn should work fine. Doing this would
also keep it from moving around from vibration. My S-40B and S-108 have
the exact same circuitry for injecting a local oscillator carrier to mix
w/ the IF signal coming out of the 1st If amp stage via T2.

For anyone that owns an S-38 (not applicable on the a,b,c,d or e
version), or a National NC-188, their gimmick wire wraps around the wire
that connects the 2nd IF amp output transformer to the plate of the
detector tube. This works OK if all you want to do is listen to CW but
produces poor results for listening to SSB. Just unwrap the gimmick wire
and move it to the same equivalent wire that feeds IF from the 1st IF
stage output transformer to the control grid pin of the 2nd IF stage. In
other words just like it's done on the S-99, S40 and S-108. This makes a
vast improvement in audio quality when listening to SSB on S-38's and
NC-188's. Reason is none of these receivers have a true product detector
stage, but the pentode tube used in the IF stage acts as a much better
virtual product detector for mixing the IF and LO than a diode detector
tube does.

regards,
   Mark
   KJ4FJK

N8IE wrote:
> THANKS!
> I un-wired mine and let it loose near the pin and it works fine.
> I guess I need to secure it so it does not move when bumping the radio
> around or moving it.
>
> You guys a great, thank you all!
>
> 73
> Dan, N8IE
>
> -----Original Message-----
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of rbethman
> Sent: Tuesday, February 03, 2009 4:11 PM
> To: hallicrafters at mailman.qth.net
> Cc: ANTHONY CASORSO; n8ie at woh.rr.com
> Subject: Re: [Hallicrafters] More SX99 questions
>
> Dan,
>
> The end that you found loose?  Do NOT solder it!  It is indeed the
> "gimmick"!
>
> The insulated wire is simple left extended outside the shielding.  I 
> just
> pullked mine out of its cabinet.
>
> Bob - N0DGN
>
> n8ie at woh.rr.com wrote:
>
>> Thanks Bob,
>> Can anyone confirm this easily?
>>
>> When the problem first happened, switching the AM\CW switch made no
>>
> difference and only a local broadcast station could be heard with the 
> volume
> cranked. I found the wire loose and soldered it back to V5. This fixed 
> the
> problem except now when the AVC is on, I get a loud squeal, but the
> sensitivity works fine otherwise. Sounds like it just slipped far 
> enough
> away from the tube to loose coupling.
>
>> I appreciate all the help guys!
>>
>> 73
>> Dan, N8IE
>>
>> ---- rbethman <rbethman at comcast.net> wrote:
>>
>>
>>> Yep, that is "another" method of creating a gimmick.
>>>
>>> If I'd dig out my SX-99 and look, I could confirm it.  It is sort of
>>> buried right now.
>>>
>>> Another project with too little time.
>>>
>>> Bob - N0DGN
>>>
>>> ANTHONY CASORSO wrote:
>>>
>>>
>>>> I the Halli sets I am familiar with, the gimmick is just a piece of
>>>> standard hookup wire stripped on one end only. The stripped end is
>>>> soldered per usual but the other end is just wrapped around a tube
>>>> socket pin to provide a few pf of coupling. It should not be
>>>> connected directly.
>>>>
>>>> Tony
>>>>
>>>>
>>>>
>>>>> Date: Tue, 3 Feb 2009 14:10:22 -0500
>>>>> From: rbethman at comcast.net
>>>>> To: hallicrafters at mailman.qth.net
>>>>> CC: n8ie at woh.rr.com
>>>>> Subject: Re: [Hallicrafters] More SX99 questions
>>>>>
>>>>> Dan,
>>>>>
>>>>> A "gimmick" is a low value capacitor that is made by twisting what
>>>>> is usually enameled wire a "few" turns. They were normally a low
>>>>> voltage component.
>>>>>
>>>>> Bob - N0DGN
>>>>>
>>>>> n8ie at woh.rr.com wrote:
>>>>>
>>>>>
>>>>>> While working on getting the SX99 back up and running I have
>>>>>>
>>>>>>
>>>> another question.
>>>>
>>>>
>>>>>> One of the main faults was the wire running from pin 3 of V5 to
>>>>>>
>>>>>>
>>>> pin4 of V4 came off. It did not look like it was originally on very
>>>> well to begin with.
>>>>
>>>>
>>>>>> This wire is shielded and in the schematic is listed in part as
>>>>>>
>>>>>>
>>>> C38 Gimmick 2uF.
>>>>
>>>>
>>>>>> Exactly what is a "gimmick" capacitor?
>>>>>>
>>>>>> Thanks es 73
>>>>>> Dan, N8IE
>>>>>>
>>>>>>
>>>>>>
>>> --
>>> Bob - NØDGN
>>>
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>>
>>
>
> --
> Bob - NØDGN
>
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