Please - this is a simple technical question about the Alpha 89. No
lectures about the evils of using ALC, etc.
I recently acquired an Alpha 89 amp from the original owner and am
checking it out thoroughly. The only problem I see is that no ALC
voltage appears at the ALC jack on the rear panel, regardless of the
setting of the rear panel ALC pot. It seems to me that the ALC voltage
is developed by U1C on the power supply board and that it's based on the
grid current which must be measured between the -HV rail and ground.
(Haven't been able to discern exactly where that is sourced in the
schematic). At any rate, the grid current monitoring obviously works as
the Grid Current LED meter reads properly. But, no ALC voltage at all
with grid current showing up to around 100 ma on the meter. I would
think that I should see a gradually increasing ALC voltage (in the
negative direction) as the grid current increases. Can anyone familiar
with the circuit comment? Thanks for your help.
73, Floyd - K8AC
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