[Collins] 32S-1 band oscillator

[Al Parker]

Hi Jerry,
	Many thanks for the thoughts.  My screen voltage is in the 150v range, 
as the skem says.  (the chart in my manual says 85 also.)  The screen 
bypass cap may be it, caps are tough to check in ckt without opening one 
end, I'll see what I can do this AM.  I have a bunch of silver micas so 
can just replace it with the right one.  It's 130 per my 32S-1 skem. 
I'll also ck or replace the cathode bypass, a 0.01
	I'm sort of suspecting a combination of things a bit of spec is 
contributing to the problem.  I do have some xtals that don't oscillate 
in either rig, and some others are probably weak.  A 15mc xtal is 
pushing the limits I suspect.
thanks for your help, I'll let everyone know just what fixes it.
Al, W8UT

On 1/21/2011 8:22 PM, Dr. Gerald N. Johnson wrote:
> Haven't yet had that problem, but I have some things to check.
>
> Check the screen voltage. One schematic says 85 volts, the other says
> 148 volts likely from different bands. Indeed the tube voltage chart in
> my 32S-1 manual says 85 volts and the schematic says 148 volts. Low
> screen voltage leads to lowered tube gain. Low screen voltage might come
> from the 47K screen resistor having drifted high in value or the wiring
> or the screen to ground capacitor gone leaky. That screen to ground
> capacitor sets the feedback and its 82 pf in the S-3 transmitter, but
> they run lower voltage on the plate too. Then the cathode is run though
> a maze to the internal/external oscillator jumper plug and if that
> connection is putting resistance into the cathode circuit it cuts the
> plate current and the tube gain. Ditto a couple RF chokes in that circuit.
>
> With the tuned circuit only in the plate of the electron coupled
> oscillator with the screen feeding back to the grid through the crystals
> (modified Pierce oscillator circuit) that should oscillate as long as a
> crystal is connected. The switch section for the crystals is also
> critical to the circuit working.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>
> On 1/21/2011 2:41 PM, Al Parker wrote:
>> Hi folks,
>> 	I've been agonizing over the xtal osc. in a 32S-1 I'm checking out for
>> a local fellow (new to him, no useful history).  It's refusing to
>> oscillate above 21.4mc.  I've swapped tubes and xtals with known good
>> ones.  I've ckd ckt component values, looked for svc bulletins,
>> judiciously cleaned the switch contacts and determined that they are
>> making contact, etc., all with no luck.  I re-tightened all grounding
>> screws.  It was wkg intermittently at first on lower bands, but changing
>> the band switch indexing a hair fixed that (so far).
>> 	The ckt is similar to the KWM-2A, but uses a 6DC6 vs a section of a
>> 6U8, so some values are different.  I've tried xtals that work in my
>> KWM-2A, and tubes from stock and my 32S-1.
>> 	Any thoughts&/or suggestions would be greatly appreciated.
>> tnx&   73,
>>
>> Al, W8UT
>> www.boatanchors.org
>> www.hammarlund.info
>>
>>
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