[Collins] Re: Collins] KWM-1 Boondoggle

[Dr.Gerald Johnson]

1. Popping can come from tubes too. And occasionally popping can 
come from resistors. Finding the source may require signal tracing to see 
where it originates. Capacitors most prone to failure and to causing 
popping sounds are those with the greatest DC bias; typically coupling 
capacitors with plate voltage on one end and a grid on the other end.

2. My schematic (in the 1959 edition of the yellow book) says that the line 
voltage switch S4G is not included in early models. SN 866 may be early. 
Sometimes that switch in other radios has proven delicate leading to 
damage and jumping it would make the easiest way to keep the radio 
running.

3. Be sure your bias supply is working well, not having cut off bias for 
transmitter stages can make extra noises in the receiver.

4. If you are running the radio on 6.3 volts for the heaters the solid state 
replacement for the 6AL5 is probably an improvement. When running on 
12 volts, leaving that tube heater circuit open will cause a slight lowering 
of the voltage on the PA tube heaters and a slight rise on those in 
parallel with V10. Though I see the pilot lamp dimmer causes the same 
problem on other heater strings.

73, Jerry, K0CQ, Technical Advisor to the CRA

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.