[Collins] 32S-1 grid problem

[Gerald]

On Thu, 2005-12-01 at 17:34 -0800, Glen Zook wrote:
> I have a 32S-1 on the bench right now that has an
> unusual problem in that the grid meter is showing a
> negative reading.  That is the meter "pins" below
> zero.  Now this happens immediately when the unit is
> turned on (tubes do not have time to even start to
> warm up).

Sounds like there is a leakage or short to ground on the grid side of
the meter. Some of the feedthrus on the neutralization circuit have been
reported to fail that way.

There is a black beauty C142 in the ALC circuit that will leak and cause
that symptom.

The symptom could also come from a 6146 with cathode oxide laying on the
grid, or a leak in C134 (not likely, but not impossible), C71, C62 (feed
through bypass), or C84. The ceramic disks ordinarily don't leak but
they can fail in that mode.

> 
> The indications are that something in the bias circuit
> is causing the problem.  However, there is another
> problem and that is the fact that the grid circuit is
> completely different from my 32S-1 manual and from the
> manual that is available from the CCA website (which
> is the same as my original Collins manual).  The
> circuit is definitely "factory".  In fact, it is
> completely different from that used in the 32S-3
> series.
> 
> The serial number is in the low 29XX (fairly late
> model).  I checked my 32S-1 which has a serial number
> less than 70 higher (high 29XX) and the grid circuit
> is the same as the one on the bench.  Obviously there
> was a fairly major production change.

Serial number means NOTHING about age. They were issued in random order.
> 
> Does anyone have a schematic of this later version of
> the 32S-1?  Also, has anyone run into the problem of a
> negative reading in the grid position?
> 
So far I only know of two neutralization circuit variations. One uses an
8-50 ceramic trimmer for neutralization, the other uses a 1.7-8 air
trimmer. It is possible that there was a transition circuit from 32S-1
to 32S-3. Other than the trimmer change (and the capacitor in series
with the neutralization trimmer) I don't see a significant difference
between my 32S-1, 32S-3, and 32S-3A manuals. Once the correction in the
next paragraph is made. Of course the ALC rectifier in the 32S-1 is a
6AL5 tube and in the later radios it is a pair of silicon diodes.

Comparing a 32S-1 manual to 32S-3 and 32S-3A, I see an error in the
32S-1 manual. There is a dot missing where the lead from C69 goes
towards C71. C69 should be connected in parallel with R108 and C70. This
error is also present in the 1959 Yellow Book (Fundamentals of SSB). Its
missing in both my 4th and 7th edition 32S-1 manuals.
> 
> 
> Glen, K9STH
> 

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer