[Amps] Gettering GU-74B's in-place with screen voltage?

[Carl]

American external anode tubes with indirectly heated cathodes are 
rejuevenated by running filaments only for a day or two in extreme cases. 
These are 8874, 3CX800, 8877, 4CX1000A, etc

Directly heated tubes have the gettering material on the inside of the anode 
surface and require running at rated power on a regular basis. The 
alternative is the same as glass tubes....run reduced plate voltage and more 
positive bias to reach a high enough dissipation to activate the getter. 
These are 3CX1000, 3CX1200, 3CX3000, 4CX5000, etc.

Ive no idea what the Russians use for gettering and dont want to make a 
WAG....

Carl
KM1H


----- Original Message ----- 
From: "Jim Barber" <audioguy at q.com>
To: <Amps at contesting.com>
Sent: Monday, March 12, 2012 2:47 AM
Subject: [Amps] Gettering GU-74B's in-place with screen voltage?


> 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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