[R-390] Bottom 200Kc Dead

[Drew Papanek]

John Page wrote:

"My Collins R390A just suddenly developed an odd ,to me, problem. It
suddenly decided it would not receive anything from X.200kc down. This on
ALL bands. Really didnt have a clue as where to start as signals from
200kc up were great. It was as though you flipped a switch when you tuned 
below
200kc on any band."

As Dave Wise (he truly is) pointed out, your PTO may have Field Change 7 
installed.  That changes the value of the screen resistor with the intent of 
reducing radiated signal.  Low(er) screen voltage may cause the problem you 
described.

Someone else had the same problem a while back.  The cause turned out to be 
low PTO tube heater voltage caused by a defective BallasTube.  Replacement 
of the 6BA6 was the temporary solution.  Verify correct heater voltage at 
PTO tube with tube in socket.

Those BallasTubes can fail in ways other than going open, and some were out 
of spec to begin with.

Drew

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