EH Scott Radio Enthusiasts

The Fine Things are Always Hand Made

Maybe someone has run across a similar situation as I am encountering. AM reception is nonexistant except for static. FM works fine. We have discovered what appears as phantom voltage of negative 300-400 volts at the grid of 6J5 AM oscillator. It fluctuates wildly when lead is copacativly coupled with my hand and pin 5 is moved we can hear a station but need to wiggle the lead with our hand. Sounds strange I know, but looking for ideas since all surrounding resistors and micas test excellent.
Thanks for reading and for any direction you may have.
Bob

Views: 64

Comment by Norman S Braithwaite on June 22, 2012 at 12:13am

Bob:

Some volt meters will read the DC voltage plus the RMS value of the oscillator signal.  A good working oscillator will produce over 100-volts RMS.  Still, the voltage you are reporting is high as if there is a parasitic oscillation.  Check the socket to make sure the pin crimps within the socket are all making good contact with the 6J5 tube.  Also try another 6J5 tube.  What are the plate and cathode voltages?  If your voltmeter indicates DC plus RMS, bypass these elements to ground for the DC only measurements.

Norman

Comment by Robert Jackson on June 22, 2012 at 1:15am

Thank you Norman.

We will let you know what we find.

Bob

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