[Milsurplus] Capacitor failure? Resistor Failure? Suggestions?

[Dean Kellogg]

I have a most vexing problem with a BC653 transmitter.

When first turn on the transmitter and try to zero-beat the MO circuit, 
I get a beat frequency for about 5 minutes.  After that....it 
disappears.....
If I turn the power and emission switch to off, I can hear the beat 
come back for a few seconds as the dynamotor rpm's drop.  If I then 
turn the transmitter back on...the beat freq returns for a few seconds 
as the dynamotor powers up and then it disappears again.  This will 
repeat itself for multiple cycles.  Only on the initial power up does 
the beat freq last for more than seconds.

SO....does this sound like a capacitor problem...or a resistor problem?