[Collins] KWM-2A changeover recovery question, etc

[Dr. Gerald N. Johnson, electrical engineer]

The open relay contacts are very picky about movement. More likely one
that enables the receiver is slow to make contact because its been bent
from burnishing to barely touch. These relays can't handle burnishing
with a burnishing tool. Anything thicker that cotton rag paper and
DeOxit can bend them.

Slow recovery could come from the fact that tune mode injects an audio
tone that drives the VOX circuit. A high VOX gain and long time constant
would slow the drop out of the VOX relay.

You need to check for grid current with drive in the tune mode to see if
they driver and PA grid tuning is correct. Each band has its own trimmer
and often a fixed capacitor on each of the rack tuned coils. Those may
go open. Switch contacts may go open, and need a quarter drop of DeOxit
on each. The RF you see with the RF volt meter may be sign of a stage
oscillating at VHF, grounding of the circuit shield boxes under the
chassis is critical to preventing that unwanted oscillation. A bit of
DeOxit on where those contact the chassis should be effective. Though
I'd lean towards a drop of aluminum connector grease. On many bands (and
I'm having trouble with the bandswitch details, I think the draftsman
was confused on the paper schematic I have) there are separate
compression mica trimmers in parallel with the load capacitor so that
all bands tune a 50 ohm load with the load variable capacitor at the
same place on its dial. Those compression mica trimmers are relatively
fragile and are known to short and thus prevent there being any output.

Does it receive on 10 meters, and are those 10 meter signals, not 11 or
12?

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.