> > Is there any service and/or alignment information available for the
Hercules II amp?
>I've never seen anything beyond what is in the manual. In other words,
not much.
There is not very much needed. Sure would be nice if it was there though.
There are a total of eleven potentiometers that can be adjusted.
I suggest the following order of adjustments:
1) The four bias control pots, adjusted one at a time while monitoring
the idling collector current of the appropriate amplifier section as the
bias to that section is adjusted.
2) The meter and bar graph calibration pots in no particular order.
Perhaps skipping the "REV" power pot until you get to the final "AGC IC"
adjustment.
3) The "AGC" pots. Probably the "AGC F" first and the "AGC IC" last.
Out of those eleven adjustments five only control what the front panel
meter and bar graph indicator show. They do not actually have any direct
effect on the function of the amplifier. They do have an effect as part
of a control loop that includes the operator and the tx power controls
on the exciter. You should be able to figure out how to get the meter
foward power, reflected power, collector voltage and collector current
readings calibrated just by looking at the schematic. Same goes for the
bar graph forward power indicator. Even with all five of these pots
grossly misaligned the amplifier will still function normally, however
you would need to use external metering to monitor your drive and output
power levels. All these five pots do is adjust the meter readings. They
don't really "control" anything else.
The other six potentiometers are pretty important, especially the four
bias control pots.
The bias pots should be adjusted for the proper idling collector current
of each amplifier section. I used an Ammeter in the collector supply of
each amplifier section to measure the current individually to each
section as I adjusted the bias for each section. The best way to be sure
you have no drive is to have no exciter connected. In this case be sure
you have a 50 ohm termination connected to the input of the amplifier.
Of course there should be a 50 ohm termination connected to the output
for all of these adjustments. I don't have the idling bias current
specification handy.
Once the idling currents are adjusted you will want to check the
collector currents with normal drive. Hopefully they will all four be
nearly identical. When you adjust the Collector Current meter
calibration you will want it to indicate 4X the current on one amplifier
section. Of course this will only be correct if they are all equal. A
clamp on DC current probe would be really helpful here. You could run
all four amplifier section collector supply leads through the current
probe together to get the real total current. You would probably have to
fabricate some longer jumpers that go from the DC distribution board to
the amplifier boards to accomplish this. You would want them to all be
identical length and wire size to have equal resistances.
While the indicator adjustments don't really have any effect on the
function of the amplifier, having the meter calibrated properly would be
a real big help in making the two "AGC" adjustments. And it is also very
helpful while actually using the amplifier.
The remaining two potentiometers control the thresholds of output power
and collector current which will actuate the OVERDRIVE LED and the input
attenuator relays. I don't know of any way of adjusting these without
actually overdriving the amplifier to test them. You should make these
adjustments in small steps using short transmissions, with plenty of
cool down time between transmissions. You might want to use two
different impedance loads on the amplifier to make these adjustments. A
normal 50 ohm termination for the "AGC F" forward power threshold, and a
lower impedance, such as two 50 ohm terminations parallel "tee"d
together to adjust the "AGC IC" collector current threshold. With a 25
ohm load you should be able to get full collector current at much less
than full drive power. Obviously you want to be very careful with your
drive power level while you are doing this. And you want to keep
transmission times short and cool down times long. If you are using a 25
ohm load to get full collector current at less than full drive and full
power output, you have a 2:1 SWR. This is a good time to adjust the
reflected power meter calibration.
If you do not understand fully what this procedure does and how it going
to accomplish the task, then don't try it. You could easily blow up a
set of power transistors if you are not very careful AND fully cognizant
of what is going on.
DE N6KB
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