Discussion in 'Amateur Radio Amplifiers' started by WO4K, Jun 26, 2017.
AL-811H has ALC output -- it works fine.
And, that's how it started....
But it doesn't detect the grid current !
So it's not really Automatic Linearity Control.
As I say, if Amps had proper ALC detection circuitry, it would not only keep them from splattering, it would also protect the Valves.
It is a good measurement of the output from the exciter though Roger. It's just labeled wrong. SB RF input voltage --- not ALC.
Keep em lit Regards Jim
It's the GOP-100 Grid Overload Protection Module for $39.95 that automatically disables the amplifier when excessive grid circuit occurs.
The point is that if ALL Amplifiers had a proper ALC Circuit, that monitored the Grid Current, and told the transceiver to reduce the drive once the Amplifier Valves' Grid Current became too high, people's Valves would last a lot longer . . . and signals would be a lot cleaner !
I'm surprised nobody makes/sells a board that you could fit in any GG Amp that would do this ! You could then just wire it to the normal ALC Output socket on the back.
Minimizing Ig is great, but the main cause of 811A failures is excessive plate dissipation (mistuning, or too-long tune-up times, or just loading to excessive Ip).
If you watch Ig while LOADing almost any kind of vacuum tube amplifier, you can see the very obvious impact loading has on grid current. "OverLOADing" an amp (tuning for max output, then adding more LOADing by reducing the load capacitance) can result in low grid current, reduced IMD and nearly maximum output all in one adjustment, and it's easy to find.