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In Reply to: RE: HK Citation 2 rebuild questions posted by DAK on April 13, 2015 at 01:45:39
It amazes me that great amps use a half-wave bias supply. However, most amps get away with it, meaning that hum can be below the audible level. Nonetheless, it's difficult to see how a full-wave well-filtered supply would be a degradation.
Do not regulate the C- unless you also regulate the B+. You want the bias to track with the B+ in magnitude so that as the B+ goes up (causing the tubes to conduct more) the C- goes up, causing the tubes to conduct less.
Follow Ups:
I would need a really good reason to build a FW bias supply into a push pull amplifier. First, the extremely light load involved makes it easy to reach ripple levels of less than a millivolt, even with only a small CRC filter. Add to that the fact that ripple applied in phase to both grids cancels in the transformer, and that NFB pushes it down even more, and it's just not an issue. Like they say, if it ain't broke, don't fix it. :)
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Buy Chinese. Bury freedom.
Edits: 04/13/15
As I stated, hum is usually not an issue. But if done in solid state there's simply no reason not to go full wave. It's about a dime in extra parts.
And if you go with a solid state C- vacuum state B+ you've definitely got C- before B+ which is a good thing!
I guess in tubed amps the rule might be, "C before B except if everything's regulated."
"But if done in solid state there's simply no reason not to go full wave."
It's not the cost, it's the inclusion of unnecessary parts. Do you think every manufacturer going back to the '50s or '60s got this wrong?
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Buy Chinese. Bury freedom.
In the 1950s and 1960s it wasn't 10 cents in parts.
And we've beat this to death. I'm done.
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