[Collins] 32 s 1 self oscilation

[Dr. Gerald N. Johnson]

On 4/20/2012 9:45 AM, drleborgne at aol.com wrote:
>
> Dear collins colleagues: My 32 s-1  seems to self oscilate  consuming transmitter power in the bands above 7.2 Mg.
> Any suggestions where the problem might be ?  thanks&  73 KI4JRY   Martin
> ______________________________________________________________
>
Most commonly the driver, feedback, and PA neutralization has to be 
performed every time tubes are changed. Poor neutralization will cause a 
stage to oscillate, more often on the higher frequency bands. There is a 
feed through bypass in the PA grid circuit, that is part of the 
neutralization circuit that has been known to fail.

Its worth the effort to loosen and tighten each tube socket mounting 
screw because grounds depend on those being tight and not corroded. Same 
thing for every screw mounted ground lug.

Sometimes the shield cans underneath each coil position lose their 
ground contacts. They can be loosened, the contact points cleaned with a 
contact cleaner, like DeoxIT, and then retightened.

Misalignment of the rack tuned to the crystal frequency, not the signal 
frequency can contribute RF power with no audio on SSB. Bad balance of 
the balanced mixer can make that worse.

Lack of carrier supression is a problem with the original two diode 
balanced modulator but that shows on all bands. See 32S-1 SB-2 for an 
update.

The feedthrough capacitor and shield grounded is discussed in Service 
information letter 1-75 which I have attached to my direct response.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association