Hi Eric,
There are several potentiometers on the 81426 Control Board in the
Hercules II. My owners manual does not explain the correct way to adjust
any or them, nor does it include a narrative description of the function
of each board in the unit , the way my Omni VI manual does for it.
Having said that, it appears to me that you could adjust R4, the 100 K
BAR potentiometer to calibrate the bar graph. Adjustment of R4 would not
seem to have any effect on any other part of the amplifier, most
importantly the protection circuitry. So you could probably twiddle R4
to your heart's content, to make the bar graph show whatever you like,
with no danger of setting it in a way that messes up the function of the
protection circuitry. R3 and R7 appear to be the ones you do not want to
adjust, unless your really understand how to do so properly.
The LED labeled "OVERDRIVE" on the front panel, is called the "FAULT
LED" everywhere in the schematics, and it actually indicates various
fault conditions, some which can be caused by overdrive. There is not
actually any circuitry that directly monitors the input RF drive to the
unit. Overdrive is determined based on over power output or collector
current over draw. Another condition which would be detected as a fault
is excessive reflected power from the output low pass filters, using the
circuit including T1, D1 and D2 on the Low Pass Filter board. An
improper load, or having the wrong band selected would probably activate
this fault indication.
I do not recommend making any RF power meter calibration adjustments,
unless you are really confident of both the accuracy of your method and
the indicator you are using as a standard.
Ken N6KB
Eric Rosenberg wrote:
Just put the station back together in time for the start of the 10m
contest. I've run into a couple of quirks with HERC II that I had
forgotten about. I am baffled by the Overdrive light and bar graph.
Overdrive:
With power set at '49', the peaks out of the amp are ~360 watts on on RF
Applications VFD digital watt meter. That's approximately where the
overdrive light goes on. The signal doesn't seem tp be distorted -- at
least it doesn't sound that way on the monitor and I've had no reports.
Bar Graph:
I realize it's impossible to compare the VFD when operating SSB. Key
down (TUNE and CW), the bar graph shows far more power than the VFD
does. Any way to calibrate or reset or correlate the bar graph?
Thanks + 73,
Eric W3DQ
Washington, DC
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