[Boatanchors] 813 grid to filament short

[Rob Atkinson]

This is all true and technically it is given a green light if mounted
with the pins oriented properly.  The problem is some tubes may have
had manufacturing defects such as the electrodes not quite properly
aligned and heat plus a horizontal mount exacerbated the problem
enough to cause a grid - filament short.  This is what I have been
told; it may not apply in your case.  Sorry you have had difficulty
with your rig.  The good news is 813s aren't quite the unobtainium or
expense of 211s or 845s or HF300s.   I'd get another 813 and give it a
try.  If the bad one was one of the modulator tubes then I'd pull the
two in the final and use them for audio and run the one good one left
and the replacement in the final.  This assumes the PA has them
paralleled and not push-pull.

73

Rob
K5UJ

>
>
> Well I'm an intelligent person, I think. At least intelligent enough to read
> the manufacturers data sheet that says " in a horizontal position, the base
> pins No2 and No6 should be positioned vertically one above the other"
>
> Then of course there's those beautifully constructed 813 amps in the 1968
> ARRL handbook
> http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/68hb195.pdf.
> Yes the tubes are on their side, and that seems like a quite an intelligent
> article also.