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In Reply to: Pentode Driver, SE output, and high frequencies??? posted by maynardg on March 17, 2007 at 14:15:15:
I remember Pete Millet noting the same issue and suggesting, in the audioxpress writeup of his E-linear amplifier, a small valued capacitor from pentode plate to ground to roll of the high frequencies . He was using a D3A pentode driver.Here's the schematic link from his site. The 1500uF/600V cap is what he used.
http://www.pmillett.com/file_downloads/KT88_SCH.PDF
Follow Ups:
correction, .. i meant 1500pF (not 1500uF), .. but the schematic's correct.
Well, I put in 820pf polystyrene, and it is much better. Now the differences between the 717A driver and the 6SJ7 are much more subtle and will take some more listening. There is an obvious gain difference. Maybe I'll have to adjust the NFB down just a bit - but don't want to lose control of the bass.Darn this is a fun hobby.
If you do ever feel like tinkering some more with your project, I thought I'd suggest you study that schematic I linked. It uses the UL tap of the OPT to supply the driver plate. It also uses regulated screens on the driver
You know, I've been looking at that off and on. My April 05 AudioXpress got lost somewhere so it awaits me rounding up another.
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