In Reply to: active loading with parallel feed? posted by DanK tubes on February 12, 2011 at 21:59:00:
It sounds great this way, no question. Finding the right parafeed cap is still a difficult problem though - the OPT inductance is all over the map as a function of frequency and voltage. The solution as far as I can see lies in the losses - eddy current and hysteresis in the transformer core. These are never quoted as part of the standard transformer specs, and are not exactly easy to measure, or to interpret.
There is no high frequency problem, believe me!
The idea certainly goes back at least to Doc B's "Soul Sister" preamp (1998). Tucker did a 45 amp at the Vancouver VSAC this way, which is still the best 45 I've heard - yes, I believe it was a TFA-2004Ni output. I'm working on a few variants currently, and the Bottlehead Repro tape preamp uses this approach with an Altec 15095 output transformer.
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Follow Ups
- RE: active loading with parallel feed? - Paul Joppa 23:33:43 02/12/11 (0)