It turns out that the problem was the grid current indicating resistor had
opened up. Negative grid current was indicated since B- path was thru meter
instead of 1.5 ohm resistor.
First thing to check: tubes (AG6k parsitics etc.) No problem.
Second PSU. No return due to open resistor.
These problems always appear to be simple, once solved. It's getting them
solved where in the problem lies......
Serial number 566 now generating 845 watts. Close enough to factory brag
sheet for me....
>
>Was testing the output of my AL80 (not A or B, or even C!) when the classic
>phfZzt sound echoed from the cabinet. When keyed, the grid current shows
>negative and little or no RF output power. Plate voltage indicates a slight
>increase when keyed, as well.
>
>AMPS 101: where does the novice start (after shorting the B+ to ground) to
>isolate the problem. I have already swapped out tubes. Results are
>identical with either set.
>
>What is the negative grid current telling me?
>
73 from NS1Z, FN44rn
John Wilcox
871 Route 120
Rumford, ME 04276-3836
fon: 207-364-2246
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