04-12-2013, 04:17 PM
The primary of the output is what opened on both radios. The choke section is pretty close to 12 ohms on both. When the radio is working, the total B current through the 1200 ohm resistor R11 is a little under 20 mA. With the output transformer open, the B current through R11 goes up to about 40 mA, which burns out the 1W resistor.
I'm afraid I don't have the filament transformer you recommended. However, I did measure the cathode voltage after the transformer opened. It was a tad below the value on the schematic, about 5 volts.
Does your transformer have about the same DC resistance as the original (225 primary, 0.8 secondary)? I'm not at all sure how much difference it makes.
My original has tabs that go through slots in the chassis and then are twisted to hold it into place. Whatever I use I'll probably need to drill holes and bolt it in place.
The dimensions of the original are about 1.7 inch wide X 1.3 inch tall X 1.3 inch thick. The twist tabs are 1.7 inch apart, but it looks like the hole spacing on any replacement transformer would be a little wider than that. Not a problem in this radio. There is a little room for a larger transformer.
What do you think about the Hammond 146S transfomer? One thing that concerns me is that the max DC current is 2 mA. Does it seem like the plate current of the 35L6 would be more than that?
I actually have an RCA 65U radio/phono that uses a 50L6 output tube. The transformer part number is different, as are some component values. the circuit is much the same, except the bypass capacitor goes between plate and cathode instead of across the output transformer. I've been reluctant to pull it to try it out simply because the part number is different. I'm not sure if that transformer works. It's unrestored, and I haven't got around to it yet. Schematic here: http://www.nostalgiaair.org/Resources/062/M0015062.htm
I'm afraid I don't have the filament transformer you recommended. However, I did measure the cathode voltage after the transformer opened. It was a tad below the value on the schematic, about 5 volts.
Does your transformer have about the same DC resistance as the original (225 primary, 0.8 secondary)? I'm not at all sure how much difference it makes.
My original has tabs that go through slots in the chassis and then are twisted to hold it into place. Whatever I use I'll probably need to drill holes and bolt it in place.
The dimensions of the original are about 1.7 inch wide X 1.3 inch tall X 1.3 inch thick. The twist tabs are 1.7 inch apart, but it looks like the hole spacing on any replacement transformer would be a little wider than that. Not a problem in this radio. There is a little room for a larger transformer.
What do you think about the Hammond 146S transfomer? One thing that concerns me is that the max DC current is 2 mA. Does it seem like the plate current of the 35L6 would be more than that?
I actually have an RCA 65U radio/phono that uses a 50L6 output tube. The transformer part number is different, as are some component values. the circuit is much the same, except the bypass capacitor goes between plate and cathode instead of across the output transformer. I've been reluctant to pull it to try it out simply because the part number is different. I'm not sure if that transformer works. It's unrestored, and I haven't got around to it yet. Schematic here: http://www.nostalgiaair.org/Resources/062/M0015062.htm
John Honeycutt
