[Collins] No Drive on KWS-1

[Gerald]

On Thu, 2005-12-22 at 10:22 -0800, Ed Simeone wrote:
>  Greetings,
> 
> I recent purchased a KWS-1 that is in fine physical condition but while
> tuning up the unit all drive suddenly went away.
> 
> We replaced a bad choke in the final drive section and one of the silver
> mica caps that was varying with temperature but still nothing. 
> 
> There is not even a hint of drive on 80 meters.
> All the voltages look good on 40 meters all the way through the final
> pre stages but still no drive.
> Any clues as where to look next?
>  
> 
> Ed Simeone
> 
> K6EGS

No drive, all bands?

Single band failure I'd look at switching. Multiple or all band failure,
still the switches are suspect. Might be helped by working the
bandswitch a few times end to end. That often brings back bands in 32S.
The longer term cure is a quarter drop of DeoxIT per switch contact.
Applied from a dropper bottle, not from a sprayer.

Otherwise in a linear transmitter the loss can be anywhere from
microphone input to PA grid circuit including ALL the oscillators.
Though the HF crystal oscillator is out of the circuit on 80 meters. I
see from the schematic in my KWS-1 manual that carrier is created by
unbalancing the balanced mixer, so if the carrier oscillator isn't
running that's the beginning of signal for tuning. Could be anything
between there and the PA grid except the HF oscillator. You just have to
trace signal starting with the carrier oscillator and chase it through
until it doesn't go through a stage. Figure 6 to 10 dB loss in a mixer,
but gain in all other stages. Check each mixer for LO injection level
compared to the level specified in the manual. Mixer gain goes up and
down with injection level, but in some mixers below a certain injection
eve there's no more mixing action on normal strength signals.

Trimmers, switch contacts, tubes, mechanical filter, all are suspect and
can only be eliminated by signal tracing once you are sure that all the
DC voltages are correct and none are shorted by old paper capacitors. Be
sure to check for negative bias on the ALC line. Lots of negative bias
there can shut down the gain stages.

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