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

[Leigh Turner]

I agree here Jeff.

Sans doing a hi-pot test on the tube as Jim suggested verifying its
withstanding voltage, I'd install a fast HV fuse and glitch resistor in
series with the plate feed, enabling the tube to benignly glitch on occasion
without incurring damage to the tube or PS components.

If the tube specimen is initially borderline, it will likely gradually
improve with a longer gettering soak to improve, harden, and stabilize the
vacuum quality.

The GI7B is indeed a great tube and excellent bang for buck.

Leigh
VK5KLT

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jeff Blaine
Sent: Saturday, 26 October 2019 1:58 AM
To: amps at contesting.com
Subject: Re: [Amps] What limits DC plate supply voltage for GI7B?

I ran a pair at about 3KV for a long time.  Once you get beyond about 
2400V, the risk of a glitch goes up.  The transformer had a variety of 
secondary taps and I could dial it in pretty close. Tube is more 
efficient and has less Ig for a given PO at the higher voltage which 
helps so it's worth the work.

And it depends a lot on the tube.  Some samples will do fine at the 
higher voltage, others not so.  In my case getting the heat out was the 
challenge.

If you go this route make sure you have well protected the PS as you 
should expect glitching.  It's a great tube for the price.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com



On 10/25/19 8:09 AM, Alan Ibbetson wrote:

> 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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