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EL34 active-load (SRPP) parallel-feed amplifier

This is a little experiment I've been playing with.  It uses EL34's in SRPP, or active-loaded, with a parallel feed (no DC) output transformer.  Running on a B+ of 600-650V, it puts out around 8 watts.

I connected the lower EL34 as a triode, and the upper as a pentode.  This arrangement provided low distortion and really good PSRR.  Details forthcoming...

I tried both a Radio Shack 70V line transformer and a Hammond 125J as the OPT.  The RS worked pretty well for a really cheap TX, but distorted pretty badly below 100Hz.  The Hammond 125J did better, fairly decent at 20Hz up to a couple of watts.

I used a hybrid tube/SS rectifier to get ~650VDC from a 270-0-270 VAC transformer.  This worked really well.

Schematic (PDF file, 31k)