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Power Supply questions

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Power Supply questions Empty Power Supply questions

Post by joeinri on Fri Feb 20, 2009 10:56 am

I'm trying to adapt a Radiola 18 (mistake in earlier post - model 18 not 17) to a Zenith model 11-E which was missing the power unit when I got it. The two sets use the same tube lineup - 4, 226's - 1, 227 - and 1, 171 (71A).
The Radiola high voltage supply is 165VDC and 145VDC. The Zenith schematic calls for 220VDC and 100VDC. My question is concerning the plate voltages of the 226 tubes and the 171 tube. Plate voltages for the 226 on Zenith is 100VDC, on the Radiola - 145VDC. Plate voltage on the 171 tube for Zenith is 220VDC, on the Radiola - 165VDC. Tube spec sheets show max voltage for the 71 tube to be - 180V and for the 226 tube to be 180V.
Can I use the Radiola voltages for the Zenith? I seem to be high on the 26 tubes plates by 45v....and low on the 71 output tubes plate by 55V. It seems to me that the Zenith schematic showing HV winding of 220V is exceeding the 71 output tube max voltage rating by 40v ???
Any help would be greatly appreciated.
Confused in Rhode Island.
Joe

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Post by n0bst on Sun Feb 22, 2009 6:46 pm

It might work, but there would definitely be differences in bias for the output tube- IOW, you'd have to change a resistor or two. It's not much of a problem to bump down the voltage for the 26s by adding a series resistance. You'll probably need a decoupling cap between the resistor and the rest of the radio. .1u should do.

Scott

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Post by joeinri on Sun Feb 22, 2009 7:46 pm

Thanks Scott! I've been playing around with it for days now...my voltages are actually low for the Zenith, but did finally get a signal through....very very weak and garbled. My plate voltage on the 71 output is around 93v..not bad, 100v supply on Zenith schematic. My high voltage of 220 however, is only making it to about 150. Don't know if that's the cause of problem but am looking around the detector/volume control at the moment. The set uses a volume control in line with the 26 tube filaments to control volume. Cleaned and repaired control and working properly now, but need to replace 3 caps in the bias circuit ( from center tapped resistor to each side of the 1.5 v 26 filament line. Also one cap across the whole 26 filament line. No idea on value of these caps...not noted on schematic. I was going to go with .01's. Thanks again for the advise....I'll look some more tomorrow, getting worn out!
Joe

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