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In Reply to: RE: Is this amp's output set to Class AB1 or A? posted by Michael Samra on May 04, 2016 at 09:37:24
"What Eioc did in one of the channels was to put in a 165 ohm resistor in series with the lone 12AX7 filament to be able to power the filament with DC from the cathode voltage.I always eliminate that and put AC on fil pins 4,5,and9 as opposed to Eico's half ass setup."
You're not the only member here who dislikes that technique, but I have yet to understand why. HK did the same thing, and it's very effective.
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Follow Ups:
Effective? Are you being serious or yanking our chains? If you want a cheap way to put DC filaments on the voltage amp,that would make sense but to this day I don't understand why anyone would put DC filaments in an amplifier. If you are speaking of DHTs,that would make sense but even then I would do my best to execute other methods because I don't think DC filaments sound as good.
A friend you get for nothing,an enemy has to be bought
"Effective? Are you being serious or yanking our chains? If you want a cheap way to put DC filaments on the voltage amp,that would make sense "
Yes, that's what we're talking about. Not DHTs, not power stages. Specifically, 12AX7s in preamp/voltage amp duty. It works extremely well and the tubes last practically forever.
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Buy Chinese. Bury freedom.
Well, the left and right sides aren't identical, it's hard to like this circuit as is. If one wanted to keep it you could use pin four of the 12AX7 for, say, left, and pin 5 for right, and ground pin 9 Then symmetry would be restored and the world would be fine again :)
...to some it's clever. To others it's excessively cheap. Today's (aging boomer) audiophile abhors "cheap" no matter how clever. IOW, a cultural phenomenon. IMO, of course.
John Broskie, of tube cad journal, developed a nice parallel se amp that uses the cathode voltage off the el34 as the heater voltage for the front end tubes. I think that is a brilliant design which makes use of otherwise wasted energy. He wrote that the amp had improved bass with this feature. regards, Dak
and you want to power the preamp tubes with DC filaments,that would make more sense but I never understood putting DC filaments in any part of an amplifier unless it's for DHTs.
You then have the change in bias over time like Steve mentioned below so that will change the voltage on the filaments as output tubes lose emission over time.
A friend you get for nothing,an enemy has to be bought
He actually built it too. I guessed it intrigued him so he made the amp. If you look at the circuit it looks complex but when you trace the signal it is rather clean with few components to get in the way. I have everything i need to make the amp except a chassis. Although, i am going to use a 6sl7 to 6sn7 aikido front end instead of 12ax7 12au7. I also have to caluclate if the KT88s have enough juice to power the heaters of the 2 front end tubes. cheers, Dak
Edits: 05/06/16
...and a cultural bias that can change over time.
Really? Cultural biases? Here??? :-0
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Buy Chinese. Bury freedom.
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