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In Reply to: RE: Dadbar brought up a good point about the selenium rect. posted by Michael Samra on February 24, 2015 at 13:43:40
I think all of the 12ax7's are connected for 6.3V, but each channel has the tubes in series. The Scott schematic shows 15v for each of the sets of three, and the Sam's shows 18v. I'll be curious to see what I have there.
Dave
Follow Ups:
I would trust the Scott schematic. My 299a also calls for 5 volts and that's what I am using. Works perfectly.
Indeed.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Id go by the scott schematic.You are right,they are in series. I've rebuilt a few lC21s and a couple 130s and I never paid much attention as I usually just tune the source voltage off the filament supply.
You will notice that a pair of 2.7 ohm resistors are in parallel off the diode bridge..Clip one end of one of the one resistor that's in parallel and see if that drops the filament voltage if its too high.If you have 7 or 8 volts across each tube's filament,I would get that down to around 6vdc on the filaments.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Edits: 02/24/15
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