04-10-2013, 08:27 AM
I finally got in the parts for this radio (except the 45's). It's performing OK, as far as receiving stations, but the output is still pretty low. Distortion is low, up to the point on the volume control where the gain starts overloading the front end.
The only thing I can really see is that the +275 source is heavily loaded. It runs around 150-170 volts with the volume down and the tubes at cutoff. The only thing that brings it up is disconnecting the center tap on the output transformer, at which point it goes up to almost the full voltage from the rectifier. I've carefully checked my wiring (there were two wires switched between the 275 source and the main B+ source, but switching them to the correct connections helped very little.) and everything is OK along those lines now. The bias across the 700 ohm bias resistor is quite high, about 90 volts (which SHOULD cut the 45's off completely and allow the B+ on the plates to come UP!)
I'm open to any suggestions of what I might try.. any chance the output tube sockets are leaking?
Thanks in advance.
The only thing I can really see is that the +275 source is heavily loaded. It runs around 150-170 volts with the volume down and the tubes at cutoff. The only thing that brings it up is disconnecting the center tap on the output transformer, at which point it goes up to almost the full voltage from the rectifier. I've carefully checked my wiring (there were two wires switched between the 275 source and the main B+ source, but switching them to the correct connections helped very little.) and everything is OK along those lines now. The bias across the 700 ohm bias resistor is quite high, about 90 volts (which SHOULD cut the 45's off completely and allow the B+ on the plates to come UP!)
I'm open to any suggestions of what I might try.. any chance the output tube sockets are leaking?
Thanks in advance.
