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In Reply to: RE: 12bh7 substitution in pilot sa 260 posted by pennyford on February 26, 2012 at 18:57:32
Both the 12BH7 and 6CG7/6FQ7 present the same issue. Does the filament winding of the power trafo have enough extra current? The substitutes draw 2X the heater current, when compared to the 'U7.
Eli D.
Follow Ups:
The schematic shows a "aux power socket". I assume this is to power the preamp.
The difference between a 12au7 and a 6cg7 is .3 amps.
I would think a preamp would draw at least .3 amps of heater current.
The schematic for the non-powered preamp (that I assume goes with this power amp) shows the heater line (pins 1 and 3) being rectified to feed 4 12ax7 heaters.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The powered by the amp Pilot preamp, model 210, requires a filament AC Voltage of 24V, IIRC; not simply more current drawn off the 6.3V AC fil. winding of the amp. The Pilot 232 and 260 amps' power trans have the 24V winding in addition to the 6.3V winding. The power trannies from Pilot were not cool running; even without the preamp being powered. However, like Tre, I don't think .3A of 6.3V will blow the power tranny. It might not even make any difference to the power tranny. If the 6.3V changes to 6.1V, at the same "in from the wall" voltage, then I would be concerned. Otherwise, I would keep using that 12BH7 or 6CG7...
I'm really getting sloppy.
I didn't see that the X Y winding was dedicated to the preamp.
Sorry for any confusion I have caused.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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