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

[stan]

I have what's basically a Clipperton QRO that I've been converting to 
GI7BT tubes. Still yet to finish that project but I've gotten one step 
closer by having a custom PCB made that duplicates the tuned input 
circuits of the Clipperton QRO. If anyone wants the gerber files for 
that board, contact me off list and I'll send them to you. Still 
undecided on whether to use the lower plate voltage or the higher plate 
voltage that's just below 2700 volts if I remember right.  I used the 
Ameritron plate choke. I've seen a couple of ways to attach to the 
heatsink on the GI7B plates, but I used a flat piece of copper and made 
a washer of appropriate size. Then I soldered the suppressor to copper 
washer and used a screw to attach the copper washer to the heatsink. 
There is a tiny bit of thread left in the heatsink that one can screw a 
screw down into, so I decided to go that route. It's a metric size 
screw, but I forget what size it is.  Once I recover a bit more from a 
recent back surgery, I plan on finishing the Clipperton QRO conversion.


73

Stan
KM4HQE


On 10/25/19 9:57 PM, Roger (K8RI) wrote:
> 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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