Going backwards from 572Bs to 811As is an unusual conversion because it
results in less power. It's also unusual in that the 811A has a lower plate
voltage rating, so the HV power supply would require modification. If you
put 572B plate voltage (2400V) on an 811A, it's likely to make the tube
fail. I'd check to see that the HV isn't over 1500V before using 811As in
there...
WB2WIK/6
-----Original Message-----
From: D Conklin [mailto:dconklin@neo.rr.com]
Sent: Monday, January 23, 2006 3:37 PM
To: amps@contesting.com
Subject: [Amps] SB-200 Amp with 811 tubes?
Gurus,
Amp rookie here.
I got a SB-200 fitted with 2 811A tubes. I was assuming that this was a
plug-and-play replacement for the 572A. A local ham who
has an extensive but not detailed memory indicates that this was a common
mod due to 811 tubes being cheaper, but that it involved a
substantial amp mod and wasn't just a plug and play replacement.
I have searched the net for info on modding a SB-200 for 811 tubes and found
nothing. I also searched the QST index without luck. I
need to know the mod so that i can check if the previous owner (SK) did it
right, or if he completed it - this amp looks like it was
in the process of being refurbed at the time of his passing - maybe he was
in the middle of converting it to or from 811s.
Any help greatly appreciated - you will go over my head pretty quickly on
this stuff, so talk slowly ;-)
AI8P
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