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In Reply to: RE: Ping PJ: questions from last week posted by artsybrute on May 05, 2009 at 09:33:39
Not wanting to hijack or presume PJ's response, but I've done a little more looking at the problem of preventing unbalanced DC on the 10k winding of the 9063. You may have picked up on this already, but there's been a revival of interest in the Blumlein Garter circuit. It's been discussed at length on the Joe List and brought up here in those venues where the street-corner evangelists hang out ;-).
John Broskie over at TubeCad has published some work with the basic circuit plus some updates (although the simpler version appeals to me more). The update article is linked below and there's a link to his original musings in that article.
It's simple and elegant and it wouldn't require the potentially frequent adjustments my low tech approach would. You could implement it with active loads, choke-loads, or conventional PP with B+ feed through the primary CT. However, if you use a parafeed approach, you can still switch that stage from PP to bridged SE by lifting the CT.
Enough folks whose opinions I repsect have given it kudos that I'm giving serious consideration to revising M&C to include it (as long as I can keep my meters for the cool factor). Caveat: every application I've seen so far is in the output stage of power amps, but there is no reason it can't work in differential stages earlier in the chain. In fact, here's an implementation for a 71A PP amp that Raymond Koonce posted to the Joe List earlier this week. There's a link to the *.pdf schematic.
OK, back to your regularly scheduled Q&A.
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