[TenTec] Herc II idling collector current adjustment

[Ken Brown]

Thanks again Phil.

The PA module idling currents were not high. With the amp not keyed they 
were all zero. And keyed with no drive, they were all around 0.4 to 0.5 
Amp. I now have them adjusted to as close to 0.50 Amp as I can get.

The Ic meter on the Hercules reads 12 Amps as soon as it is powered on. 
The increase when keyed with no drive looks like 2A, but of course on a 
100 A scale, with divisions only every 25 A, that is difficult to tell. 
When putting out 500 watts it reads 75 A and maybe 80 A at 550 watts. 
The 12 Amperes being indicated at power on, with no keying or drive, 
must not be an accurate indication. I suspect a DC offset in the LM358s 
that are being used in the Ic monitoring circuitry. There is definitly 
not 12 A going to the PA modules with no drive to the amp.

I have also measured the individual PA module currents with enough drive 
to indicate 50 A on the Ic meter. This produces about 200 watts output, 
and the currents to each PA module are all very close to 10 A each. So 
the modules are all working nearly equally hard, and there is a 10 to 12 
A offset in the Ic meter indication.

Measuring full drive current draw of the PA modules would be a little 
more difficult. Most of the difficulty would be in finding the 
appropriate instrument, or making a shunt. From what I can see so far, 
there is not really any excessive current draw. I'm thinking about a fan 
for the 9420 again.

Ken  N6KB

>With the amp turned on its side, and with the front panel at the left,
>looking at the amplifier boards:
>
>Bias board pots
>R14 controls upper left amp
>R10  controls upper right
>R2  for lower left
>R6 for lower right
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