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kawasaki99 16th December 2010 06:09 AM

Odd Block Series 1 6L6 Amp Power Supply
Currently building 6L6GC PP amp using the Odd Watt schematic posted by Oddwatt Audio( 6/24/2009 ). The power supply transformer I'm using is rated 5 amps @6.5v ac. Using the bridge ,diodes and cap as specified, the dc output for the heaters drops to 4.1 volts when loaded. Is it typical for the ac to dc conversion components to drop that much voltage? Any suggestions to get the voltage back up to 6.3v would be appreciated. I'm very new to the vacuum tube hobby.
Regards, Richard

azazello 16th December 2010 07:21 AM

There is drop on bridge rectifier, I'm afraid that You can't use DC heating with this transformer with secondary 6.3 v.Try heat tubes without bridge rectifier. If You use 6L6, 5A from Transf. are small
for all tubes. You can try schematic with 6BQ5, 6AQ5/6005/, 6V6....with resistor 12-13 ohm/2 watts on each LM317.

kawasaki99 17th December 2010 04:29 PM

Thanks for the prompt reply regarding the 6L6 amp. I tested the power supply and discovered a 2.2 volt drop across the three heater diodes. By removing them from the circuit the heater voltage is raised to 6.0 volts dc but of course adding about 1 volt of ac ripple. First, are there more efficient diodes available then what is called for in the schematic and secondly is using the power supply with the diodes removed a bad idea?
Regards, Richard

artosalo 17th December 2010 05:02 PM

Are you supplying 6L6GCs with DC too ?
It is fully un-necessary. Give them AC and then to rest of tubes DC.
Then the voltage drop is much less.

kawasaki99 17th December 2010 06:17 PM

If using ac for the 6L6 tubes is the dc heater bias circuit necessary. and will it function with ac heaters? There is a strong warning on the schematic to use the heater dc bias circuit to prevent smoke and fire.

Regards, Richard

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