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bitrex bitrex is offline
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Default Tube mono-block amp with SIX 6L6 outut tubes

On 12/28/2018 08:18 PM, bitrex wrote:

If you want to see an interesting audio amp, look up the Editors and
Engineers Radio Handbook from the mid 60's. There's a design that
which uses 6 or 8 6080 double triodes to build a direct coupled
amplifier, no output transformer and dual power rails, positive and
negative. Never built built it here, but a very original design. Could
probably update that to use power mosfets...


the two big issues with OTL tube amps is the intrinsic impedance
mismatch of a tube cathode vs a tube plate in a totem pole arrangement
looking into the load, and related lack of any intrinsic power supply
noise rejection in the output stage the way a push-pull
transformer-coupled output stage has when both halves have similar
output impedances working into the same reflected load.

Global negative feedback can't do anything about the second and there
isn't usually enough open-loop gain available to do a good job of
correcting for distortion caused by the first across the audio band.
often leading to a kinda poor-performing amp.


These issues can be addressed but it requires more work than I'm
guessing they put in in the mid 60s (can't immediately find the article
in question online)