[Collins] KWM-2 #518

[Gerald]

On Sun, 2005-08-28 at 21:44 -0400, Ray LaRue wrote:
> Well after the several bad tubes, cleaning the relay contacts and 
> finding a "bad" spot on the 2nd receiver mixer gain pot, I got it 
> receiving.  Sensitivity seems now normal.
> 
> I haven't tried to load the any transmitter yet, only checked the idling 
> current and PA resonance.  They seem OK.
> 
> There are yet a few more problems on receive though:
> 
> 1.  The exciter drive peaking works well on receive, 40 meters and up, 
> but when peaking on any on the three 80 meter bands, there are numerous 
> very strong birdies (15 or 20) and several places on each band where the 
> receiver goes into feedback like oscillations.  This is with or without 
> the antenna connected, or with the siggen only.
> 
> 2.  There is little or no S-meter indication on strong signals (meter is 
> good) and poor AGC action.  (May be part of the problem causing #1.)

Have you replaced the black beauties yet? Their leakage can kill off AGC
keeping the front end gain excessively high. And almost none aren't
leaky. The impedance in the AGC circuit is high enough that 10 megohms
makes a badly leaky capacitor but that's hard to check with the VOM.
Orange drops almost never leak.

Is the receiver RF tube the proper one, or a high gain replacement? V7
should be a 6DC6.
> 
> 3. LSB and USB work fairly well, but when switching to CW, a low level 
> noise or motor boating like noise, occurs, (also could be AGC problems).

Motorboating comes from bad electrolytics on the low voltage DC line.
> 
> Don't think I know how to trouble shoot the AGC circuitry other than to 
> check static voltages, etc.

Signals should drive the AGC line negative. Backing off on the RF gain
drives the AGC line negative. Controlled tubes with grid emission will
drive the AGC line positive. Start by looking for negative voltage
rising with stronger signals on pin 4 of T5. Its possible that the AGC
rectifier tube is bad. Then trace the circuits to see where the negative
voltage gets lost.
> 
> If you have any experience on the above or can offer any suggestions, it 
> would be appreciated.
> 
> 73,
> Ray, W4BYG
> Naples, FL