[Heathkit] DX-60 Problem

[Harry Vaught]

Chris,

I was lucky with the bandswitch.  The breaks were where there weren't 
any contacts.  It looked like they broke when the mounting screws were 
tightened and no effort was taken to align the wafers and relieve the 
strain imposed by the stiff wires.  I'm not sure this thing ever worked. 
  That may be why it's so clean.

I didn't mention that I replaced R25 early in the game.  A shorted R25 
would have explained the problems at the modulator.  It checked ok, but 
I thought maybe it went bad under stress.  I also replaced the 6146 with 
a known good used one, if a little weak, I'd pulled from my Ranger. 
Your point about an inoperative bias supply at some point is probably 
accurate, the filter caps in the bias supply were shot.  I haven't found 
the 8.2 ohm resistor to be even warm since I re-did the power supply.

The power supply voltages check good at the source, indicating that the 
diodes and transformer are good.  Also, the transmitter dips, loads, and 
  puts out a good CW signal. Drive tunes and adjusts properly. 
Everything works except AM.  In AM, it puts out about 50 watts carrier. 
  I can get some audio from a monitor receiver, but it's very weak and 
the power meter on my tuner shows almost no modulation swings. 
Obviously with the voltages so much off, the modulator isn't working well.

There seems to be a general problem with bias, but the bias voltage is 
good at the source.  I don't know if the problem is one directly with 
bias, or if it's being skewed by whatever is causing the strange 
voltages at the modulator.

Thanks for your reply.  Even if nobody comes back and says, "Boy, 
replace C99 and your troubles are over", it helps to talk it out and 
look at things I haven't thought of.

Regards,

Harry, KT4AE