Might be worth checking if they need gettering. I have some old GU74bs
and a NOS 4CX800 which have been sitting on the shelf for several years
that I know of. I want to sell them so the first step was hipot - all
made 8kV at <1uA.
Can't see any problem with running them up with cutoff bias applied, I
tend to go cautiously and add a couple of 12" long 15k wirewounds in
series with the HV at first.
Steve
PS anyone interested in the tubes please contact me off list. SK1 bases
available too.
> Is there any reason I shouldn't getter a set of GU-74B's in-place in the
> amp with blower air, filaments hot, and with grid and screen bias
> applied, but with the plate caps lifted? The amp in question is a QRO
> HF2500DX that appears to be virtually unused, but also appears to have
> been stored for an unknown amount of time.
>
> Most of my experience is with metal-ceramic triodes (which "bang" after
> storage without gettering) and good-old beam pentodes like the 813,
> which don't, or at least haven't yet for me, at least. These (Russian)
> metal-ceramic tetrodes are undiscovered country, so I may be being
> over-cautious. Or not?
>
> Thanks,
> Jim N7CXI
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