[Collins] Setting ALC meter on KWM2

[Dr. Gerald N. Johnson]

On Sun, 2007-08-05 at 19:56 -0400, john wrote:
> I've made some good progress with the KWM2 I've been working on 
> reviving.  Got the T/R switching right with the replacement of C20 and the 
> two 68K resistors. Bias is now set right , and things seem be working well, 
> except for the resting position of the ALC meter.
> 
> When in SSB mode, and the transmitter enabled (PTT engaged) what should be 
> the reading on the meter in the ALC position?  Mine is reading about 25% of 
> scale, which can't be right.   Is there a process for determining if the 
> ALC is working as designed, and if so, how to re-zero the ALC meter ?
> 
> Thanks
> John K5MO
> (My first KWM2 resto...)
> 
On my old KWM-2 schematic there is an ALC zero pot probably adjacent to
the transmitter IF tube, V4. Its R30.

The ALC meter should rest at zero with PTT pushed and no audio. It
should be rising when the PA grid current starts to flicker as the audio
drive is increased. Its based on PA grid current. The PA is designed to
be class AB1 which means no grid current in normal operation. Watching
the RF output with a scope, ALC should let the peaks rise to rated power
and then keep them from rising higher even when the transmitter gain is
increased or the microphone driven harder.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer