Upon investigation, it seems that one or more of the Astrons shuts down so not
all four sections of the amp are powered. I see that, if I turn off one
supply, that there is backfeed from the amp showing up on its output. My guess
is that the one of the supplies (a little slower to come up?) senses the
backfeed voltage from another one and this triggers some protection feature.
Perhaps so, but I see no way for the back feed to occur, except through
some 100 K Ohm resistors on the DC Distribution Board. If that is enough
to trigger a protection feature on one of the Astrons, then my guess it
that one of the Astrons is mis-adjusted or is in some other way faulty.
I have only the sheet that came with the Astrons - no schematic or detailed
technical info. Tomorrow I will call them to see if they can shed any light,
meanwhile perhaps someone here has experience or insight?
Some Astrons have a terminal which is used to tie the regulation
circuitry to another identical Astron when paralleling them for higher
current capacity. I'm not sure this would help though, since the
Hercules II is really set up to run on four separate, not paralleled,
supplies.
Neither the positive supply leads nor the negative supply leads are
paralleled together in the 9420 or in the Hercules II, except when using
the cable for battery operation. I suggest you keep the Astrons running
independently, feeding the four sections of the Hercules II separately.
You also need two other voltage sources, +REG and +14v/3A to run the
control circuitry in the Hercules II. In the 9420 +14V/3A supply comes
from the other power supplies, and are only paralleled via diodes
(actually using half of some bridge rectifiers). The +REG supply has
it's own transformer, rectifier, filter and regulator.
You really should check out the schematics of both the Hercules II and
the 9420. Mine all came in one book, and even if you don't have a 9420,
you may have a schematic for it.
If these are linear mode regulated Astrons, they are probably a pretty
straightforward circuit using transformer, bridge rectifier, filter
capacitor, LM723 regulator chip and 2N3055 pass transistors.
DE N6KB
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