12-01-2007, 11:56 PM
Hello blurrrr,
The RF deck of the 38-116 Code 125 is one of the most complicated assemblies that Philco ever built. Only the RF deck of the 38-116 Code 121, identical to Models 37-116, 37-675 & 37-690, is more complicated.
Since you have changed tubes and checked voltages, check resistors (19), (21) & (22). Did you replace condenser (20)? Check continuity of the oscillator coils. It is very unusual that all five coils would be bad. How about the oscillator control circuit (6N7G and associated components)?
Have you tried feeding an IF signal to the set and seeing if it goes through? Inject 470 kc IF into the grid cap of the 6A8G mixer tube (the one directly in front of the 6U7G RF tube). Please note that it won't do any good to feed a signal into the grid of the other 6A8G tube - the one behind the 6N7G; the grid cap of the 6A8G oscillator tube is grounded. Anyway, when you inject a 470 kc signal into the mixer grid, you should hear a 400 cycle tone through the speaker. Your signal generator should be set to 470 kc with internal modulation on.
The RF deck of the 38-116 Code 125 is one of the most complicated assemblies that Philco ever built. Only the RF deck of the 38-116 Code 121, identical to Models 37-116, 37-675 & 37-690, is more complicated.
Since you have changed tubes and checked voltages, check resistors (19), (21) & (22). Did you replace condenser (20)? Check continuity of the oscillator coils. It is very unusual that all five coils would be bad. How about the oscillator control circuit (6N7G and associated components)?
Have you tried feeding an IF signal to the set and seeing if it goes through? Inject 470 kc IF into the grid cap of the 6A8G mixer tube (the one directly in front of the 6U7G RF tube). Please note that it won't do any good to feed a signal into the grid of the other 6A8G tube - the one behind the 6N7G; the grid cap of the 6A8G oscillator tube is grounded. Anyway, when you inject a 470 kc signal into the mixer grid, you should hear a 400 cycle tone through the speaker. Your signal generator should be set to 470 kc with internal modulation on.
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Ron Ramirez
Ferdinand IN
