I think the real problem at the end of the day was that the tube manufacturer
wasn't going to provide any 'design maximum ratings' for sweep tubes except in
horizontal sweep service. Realistic design maxima for ICAS linear service would
have seen some severe derating from the power levels that amateurs wanted,
anyway. I did read that many of these tubes derived originally from 6L6/807
structure: certainly, there were TV sets over here that used the 807 as a
horizontal sweep output tube in the years just after WW2 when TV was starting.
Additionally, in the ham world, the mistreatment of tubes like 6L6, 807 and 813
was legendary, and they would stand up to a lot. I ran, in my mispent youth, an
807 at 200 watts input, (Va = 1750, Vg2 = 500, Vbias about -250, driven hard by
a 6L6!) and it lasted well - but 807s were very cheap as war surplus, and I
believe, in the US, 1625s even more so. So a belief readily grew up that you
could take liberties with all tubes.
I have a seen a 2MHz marine radio over here that used 3 6LQ6 in the PA with
about 600 volts on the plates: but that was rated for 100 watts PEP out, and, I
suspect, didn't push things at all.
73
Peter G3RZP
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