02-02-2009, 08:41 PM
A couple of things come to mind. There may be a high resistance break in the input rf transformer. Very difficult to pin down. A good DMM or VTVM might pick it up - a VOM might not.
Bad solder joint associated with that grid? I would reflow the solder on the tube's grid cap because thats easy to try. You might also try replacing that tube with a known good one...or even switch it with the other 77.
Do you get the same effect if you pull the second tube's cap and replace it? How about if you disconnect/reconnect the antenna while listening?
You can check for oscillator operation by using a second radio alongside the Philco. Tune it to some random frequency about the middle of the band. Say 1200. When you tune the Philco's dial to about 940 you should hear the Philco's local oscillator carrier quite strong in radio #2.
See how it passes that test and if its the oscillator at fault we'll pick away at the options.
-Bill
Bad solder joint associated with that grid? I would reflow the solder on the tube's grid cap because thats easy to try. You might also try replacing that tube with a known good one...or even switch it with the other 77.
Do you get the same effect if you pull the second tube's cap and replace it? How about if you disconnect/reconnect the antenna while listening?
You can check for oscillator operation by using a second radio alongside the Philco. Tune it to some random frequency about the middle of the band. Say 1200. When you tune the Philco's dial to about 940 you should hear the Philco's local oscillator carrier quite strong in radio #2.
See how it passes that test and if its the oscillator at fault we'll pick away at the options.
-Bill
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