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RE: Bogen HO50 1949 AB2 vintage amp

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In Reply to: RE: Bogen HO50 1949 AB2 vintage amp posted by ivan_terrible on October 19, 2020 at 00:00:46

I have to assume you mean the Stancor Williamson amplifier CH-2133 rated at 10W??
These were sold as kits with the A-8054 OPT, and the 807 screen grids tied to the anodes in an attempt to imitate the PX25 triode.

There were major problems with Williamson amps, because without a decent transformer they turn into great RF oscillators.
As the British knew, they turned to Partridge for a proper interleaved winding arrangement.
In reality the KT66 with higher screen grid ratings is better than the 807, which is why DTN W used it.

Stancor made a Stancor A-8072 "ultralinear version" which is an anachronism. 6L6/807s and the like with their aligned grids don't basically work with "ultralinear" because the screen grids have inadequate gain.
Probably would work a lot better with the EL37, forerunner of the EL34.

Apparently Stancor, UTC with their LS series and Peerless were about the only people capable of making decent interleaved OPTs.

The Bogen amp seems to be pretty impervious to HF oscillation,I suspect because the OPT is well made and because it's AB2 is HALF the usual A-A load.

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