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

[Carl]

The problem with that and some other Russian triodes is that they are low mu 
and make poor SSB amps with poor IMD.

Running in GG takes a  lot of drive and HV for reasonable effficiency. They 
make nice Class C AM/CW tubes.

Think of the difference between several USA A3 and  A7 suffix ceramic 
triodes or go back to the 811 and 812 glass tubes.

The G17 also goes soft very easy which could be because it is a pulse tube 
and not made for high duty cycles or just a low cost throw away tube after 
so many hours.

If something like a pair of 3-500 prices makes you shudder then you may need 
a different hobby or consider other sources or the good used tube market.

Carl


----- Original Message ----- 
From: "Alan Ibbetson" <alan at g3xaq.net>
To: <amps at contesting.com>
Sent: Friday, October 25, 2019 9:09 AM
Subject: [Amps] What limits DC plate supply voltage for GI7B?


> 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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