Canadian Philco model 706A Bing Crosby (46-1201 - Printable Version

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Canadian Philco model 706A Bing Crosby (46-1201 - Arran - 09-02-2009

I though that I should mention that this radio is playing now, and quite well, what I wanted to know is if anyone has the schematic and voltage specs for the 46-1201 with a voltage doubler, not the version on Nostalgia Air with the typical AC/DC style half wave rectifier? I have the schematic for the Canadian 706A but the voltages are way off, it pegs the maximum plate voltage at 120 which seems out to lunch, the 48-1201 shows 180 VDC but there are circuit differences, a Pi circuit power supply with resistors for example. The voltage I was getting was almost twice that, no surprise for a voltage doubler, I was getting 210 volts at the screen grid and plate of the 50L6, the maximum rating is 200. As I didn't want to burn up the tubes I tried reducing the size of the filter condensers by half to reduce the B+ voltage and it made no difference, still came out at 210 volts. There was a 90 ohm resistor in series with the plate of the first diode of the 50X6 rectifier, it dropped the input voltage by about 12 volts from 122 to 110 AC, since it was burned a bit I replaced it with a wire wound 225 ohm resistor which dropped the input voltage down to 95 volts AC, now the plate voltage is down to 176 volts DC at the 50L6.
However the plate voltage at the 7C6 first audio/second detector/AVC tube is currently running at 140 volts, while the tube manual says this isn't near the maximum in flicking through my Philco service manuals I could not find another set with that high of a plate voltage on that tube, the closest was maybe in the 100 volt range. It seems that 176-180 volts DC is acceptable for the rest of the tubes as I have found similar voltage ratings in other Philcos for the 7A8 and the 7B7, and it isn't out of line for a 50L6 or 50A5. I'm thinking of installing a larger value of plate resistor in series with the 7C6, perhaps a 470k ohm in place of the 220K ohm. Does anyone have any suggestions?
Best Regards
Arran

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