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In Reply to: More questions on PP pre out posted by John Swenson on January 17, 2007 at 15:34:16:
I paralleled two plates in a single envelope in one of my Headphone amps. This is the amp that sounded the best, but it didn't have enough gain to be run from a portable CD player (A 115V player could drive it just fine.)The parts on the grids are a cross feed circuit you don't want in a preamp.
R5 and R7 worked the magic in paralleling the two tubes. R5 added to R7 should approximately equal the bias resistor R4
Play safe and play longer! Don't be an "OUCH!" casualty.
Unplug it, discharge it and measure it (twice) before you touch it.. . .Oh!. . .Remember: Modifying things voids their warranty.
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