[Milsurplus] Tube ID ?

[Kenneth G. Gordon]

On 15 Jan 2018 at 18:57, Mike Durff via Milsurplus wrote:

> I found this tube in my stash. I always assumed that it was bad, but the filament 
> lights dimly  @ 5VDC and draws about 2.25 A. It is an AMPEREX and I can read 
> the numbers XX00 on the aluminum base. It appears to be a triode, but not one I 
> am familiar with. Large plate cap covers the top of the glass and grid pin on one 
> side. Anybody recognize it or care to venture a guess? 

In fact, that 5 V at 2.25 A is exactly 1/2 of the 10 V 4.5A required by an 810. After taking 
another, closer, look at your photo, I am about 90% positive it is an 810.

810s are very good tubes.  I had a friend who had a pair of those operating push-pull in a 
home-brew all band AM/CW transmitter. I can't remember what he used for modulator tubes, 
but his transmitter output a full kW plate-modulated. He operated mostly CW and according 
to him, the transmitter just "loafed" at the then limit of 1 kW input.

810s were also used extensively in BC transmitters of some years ago. A BC station in 
Missoula, Montana had a transmitter which used a pair of those, and in all the years that I 
remember it being in operation they never replaced a tube.

Ken W7EKB

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