[TenTec] Help Understanding the Herc II Overdrive Light

[Ken Brown]

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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