MagneQuest Forum

RE: Damn I don't have a center tap in my separate filament transformer

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In Reply to: RE: Damn I don't have a center tap in my separate filament transformer posted by vanofmonks on March 02, 2008 at 15:03:50

Yes, it's just the cathode resistor... but I have found splitting the DC and AC balance works better than putting them in parallel. You could also add an additional 100-ohm balance pot and have adjustable DC balance independent of AC balance.... have done this too... helps a bit on difficult tubes, but here's always a limit on how low you can go... I do have some NOS 45 tubes that can be balanced below 120 microvolts with s/n ratio approaching 90dB referenced to 1-watt/8-ohms.... makes for an extremely quiet amplifier.

Then again, the spec'd filament transformer is only $9 from Angela. And of course.... any alterations to the circuit.... and it's your design, not mine. I've used this same technique with 2A3 triodes with excellent results, but forget this approach with single-plate 2A3 tubes.. the multi-wire filament is brutal on hum output... and I've not had any reasonable luck using AC filaments on these... plus they are extremely sensitive to mechanical vibration.

Regards, KM

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RE: Damn I don't have a center tap in my separate filament transformer - limono 20:28:43 03/02/08 (0)

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