[Collins] 32S-1 band oscillator

[Dr. Gerald N. Johnson]

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
>
>