Chuck Harris wrote:
snip
If you are using a tube that really likes to oscillate, you will need
to put ferrite beads on the leads up at the tube.

Alan Douglas wrote:
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The only tricky part would be the switching for comparing two
tubes. In the 570, the tubes are in parallel all the time, and the
unwanted grid is biased at -300V through 10 megohms. The lever switch
has three positions: in the center or "off" position both grids are
biased off. Throwing the switch one way or the other, transfers the
grid to the 570 circuitry. I presume the switch is a shorting type,
to avoid floating the grid, even momentarily.

Cheers, Alan


Thanks very much, Chuck and Alan! Two gems I hadn't considered yet,
which makes me darned glad I asked...

-ferrite beads it is; I've fabricated socket extensions in the past, and
evidently immediately forgot the learning experience (w/oscillation.)

-and the switching tubes (switching grids, and plates too maybe?)
concern; I should have been pondering that. I expect 'slightly' time
delayed relay circuits (50~100ms 'overlap') should do it (?) as I want
to have four test socket positions to rapidly go back and forth from,
and doubt I could easily come up with the right make before break switch
(? but I haven't looked yet either.)

Thanks again!
-Robert