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[Amps] What limits DC plate supply voltage for GI7B?

To: amps@contesting.com
Subject: [Amps] What limits DC plate supply voltage for GI7B?
From: Alan Ibbetson <alan@g3xaq.net>
Date: Fri, 25 Oct 2019 14:09:48 +0100
List-post: <mailto:amps@contesting.com>
The datasheet for the Russian GI7B triode says the maximum anode voltage for "continuous wave generation" is 2.5KV, so about 5KV peak. However the rating is 12KV for pulse operation. Flashover would not appear to be an issue even with a 6KV DC supply and the Ia/Va graph still looks sane at 8KV despite needing well beyond -60 volts on the grid for cutoff.

Does this mean the valve can be safely operated with an anode supply beyond 2.5KV as long as the thermal ratings are not exceeded? Or do bad things happen? If there are problems please can someone explain the physics?

The reason I ask is I've been given a 3.3KV/400mA PSU, I have some GI7Bs on the shelf, and the cost of an 8877 or even a pair of 3-500Zs these days makes me shudder.

Has anyone tried 3KV or more with a GI7B?

73, Alan G3XAQ
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