[Amps] 3CX800A7 Grid Current

[Dennis W0JX]

I have an Ameritron AL-800H here that uses 2 of these tubes. It is a great idea to measure the grid current vs output of each tube if you can. I don't know enough about the control circuitry of the Alpha 86 and if it will allow you to do this before kicks off line.
In the AL-800H, a grid current of 150ma (approx 100 watts drive) produces the maximum rated grid dissipation of 4 watts per tube and will disable the amp via a safety circuit within miiliseconds. The operating manual says "never exceed 60 ma of grid current on CW carrier." I think these parameters would apply to the Alpha 86 also.
When I received this amplifier from an SK estate, the tubes were already quite old. After a few years, the main line fuses began to blow. The tubes began arcing over. Another friend gave me a set of soft 3CX800's from his Alpha 87. They lasted about 6 months before they too began flashing over. So you can expect that if your tubes are soft, and need a lot of drive, sooner or later, as they approach end of life, they too will begin arcing over and either blow your fuses or the glitch resistor or both.
73 Dennis W0JX