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Delco Model R-1128 buzzing very loudly

I have a 1939 Delco Model R-1128 (schematic below) I have replaced both electrolytic filter caps and most of the other caps (tested the caps in the tone circuit and left them). After about 10 seconds of power on, the speaker starts to buzz very loudly with the volume all the way down. At first I thought it was the field coil buzzing, but after disconnecting the speaker from the Output Transformer, the noise went away. Any ideas?

torokj picture

Hello Will,
Remove the c25 coupling capacitor from the input pin (Grid) of the 6F6G  power pentode.If the buzz still exist,this tube,or rectifier 5Y3G probably faulty.Are the grid resistors OK?
If you have signal tracer,you can follow the IF and audio signal path.
Good luck to repair.



SzBálint picture

üdv: a csöveket is érdemes megmozgatni a foglalatokban