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

[Roger (K8RI)]

Due to the tube's design it's easy to create transverse coolers and use 
them in MLA2500s If you have access to a milling machine, or know a 
machinist.

73, Roger (K8RI)


On 10/25/2019 10:18 PM, Leigh Turner wrote:
> 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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>
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-- 
Roger (K8RI)