[Amps] Ameritron AL-811H-- Again

[Peter Chadwick]

At the end of the day, the 572B isn't that good a tube for HF. OK, it 'gets
by', but its structure isn't that good. As far as I can determine, it first
appeared in the early 1950's as a zero bias audio tube for modulators,
replacing 2 811As. About the right sort of size for modulating a 500 watt
input tx with a pair - for 1kW, you went up to 810s. Even the 811A was used
more at audio: its lower mu brother, the 812A, was used at RF but even that
was pushing things a bit at 30MHz - you had to be careful with the layout.

It was to get the grid leads shorter that tubes like the 24G and 35TG were
introduced, with a side contact for the grid.

Now add the fact that the quality isn't necessarily as good, and you're down
to getting what you pay for - or, rather, not getting what you don't pay
for.

So we're talking about amplifiers with tubes designed at least 50 years ago.
Having said that, the 4X150 first appeared in 1946: the filament structure
of the 3-500Z is the same as the 4-250, and that was a 1945 tube, too.

73

Peter G3RZP