overlooked something or made any mistakes.

Groningen, Netherlands

PS The 6N3P is a Russian equivalent of the 2C51 and 5670. In Cyrillic script it is written as 6H3PI.

     The circuit above makes all the changes. Gain should be roughly half of the mu and the output impedance less than 1k. Build both circuits and have a shoot-out between them.

Subject: active DC offset correction
     I'm sorry if you've heard this too many times before, but I'm hoping you would address the question of active DC offset correction in class AB Circlotron OTL amps. I think I've seen a commercial offering of such a circuit somewhere on the 'Net, but can't remember where. I also understand that a certain well-renowned tube amp designer (let's call him Batman ;-) has designed such a circuit that works, but is unwilling to reveal any details.


    Here is what I came up off the top of my head.  The mistake many would make would be to try to zero both triodes simultaneously by applying two DC correction circuits. I believe that would upset the bias point. The workaround is to make only one triode's cathode match the other's. This will match the idle currents and eliminate the offset, as the equal idle currents will define a zero volt differential between cathodes.

Aren's line stage

    I would use a much lower plate resistor value and use an unbypassed cathode resistor, as I believe a lower gain and a higher current draw could only improve the sound of this line stage.

Active DC offset correction for the
circlotron output stage

Remake of Aren's line stage


www.tubecad.com   Copyright © 2001 GlassWare   All Rights Reserved