With regard to the comment about using 811-As rather than 572Bs, better
first check the plate voltage. 572Bs can be run up to around 2.5KV while
811As are typically run around 1.5KV. Since the Clipperton-L was
originally designed for 572Bs, I'll bet the plate voltage is too high for
811As.
Also, sometimes cheaper is false economy. While I was going to college
(translation: poor with no money) back in the late seventies, K5GO loaned
me an old Gonset GSB201 to make me QRO on the bands. This amp was
originally designed for 811As but had been retrofitted with 572Bs, two of
which were unfortunately, shot. Scrounging around the storeroom in the e/e
lab at the college I attended, I found four unused, govenment-surplus 811As
in boxes. In the Gonset these tubes would do 1KW out when driven with my
SB-401 and I was a happy ham.
However, after a year I opened up the case and noticed that such operation
had abused the tubes pretty badly. Two of them had holes burned thru the
plate, while all four had warped heat radiating fins. At that point I
swapped the original 572Bs back in and returned the amp to its owner.
73,
Dave/K8CC
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