Here are some instructions
for how to properly tune your Kenwood hybrid transmitter. It takes longer
to describe than it does to actually tune the rig! When you have done it a
few times, you can tune up in about 5 seconds total, faster than it took you to
read this paragraph!
- Begin tuning with the Mode
Switch in the Tune position. That reduces the
screen voltage, and mis-tuning won't harm the rig. Start with a dummy
load if possible.
- Set the Load Control to
Minimum, and dial in the
band (approximately) on the Plate control
- Set the Meter Switch to
- Turn the CAR Control
(carrier) up 1/2-3/4
- Place one hand on the Send switch
and the other on the Drive control
- Flip the Send switch and peak the
Drive control. If the meter pegs, turn down
the CAR control and peak Drive
- Switch Meter to Ip (plate current)
- Flip Send switch and tune the
Plate tuning to dip the Meter (minimum
reading). This is usually the max power output point as
Now you're ready to go for
some power! As you perform the steps below, don't leave the rig in Send
more than 5 seconds at a time. Give it a rest now & again as you get
familiar with this. Most of us can tune a rig in about 5 seconds total,
you will too when you've done it a few times!
- Switch Mode to CW
- Flip the Send switch and re-dip
the Meter with the Plate control
- Note the Meter reading - You are
looking for about 225ma,
depending on your power needs - About 1/3 to 1/2 less for PSK or
- It will probably be low. Turn up the
Load control about 10 degrees, and re-dip the
Plate control. Continue doing this until you get about
225ma of plate current when dipped. Remember not to leave the rig in
Send too long while you're learning, give it a 5 second
rest every 5 seconds.
finished! Transmitting at this point would be fine, but you may be able to
tune for a bit more power. The next adjustments should be small
adjustments, you are "fine tuning" things at this
- Switch your Meter to
RF, or use an external
power meter for reference.
- Tune the Plate control for
maximum power output. You should see about 100W if you have a power
- Try adjusting the Load up or down
a bit, re-peaking with the Plate tuning after every
- When you're satisfied with your tune-up, check Ip,
the plate current, and make sure you're not too far from the 225ma target, and
note the position of the controls to use this as a starting point whenever you
return to this band.
- For CW, use the CAR control,
and for SSB, use the
MIC control to keep the ALC within the range
shown on the Meter. This will insure maximum power output without
Things to Watch for While Tuning
Tune-up is a good
time to check your rig for maintenance requirements. Your Kenwood hybrid
is an excellent tube tester, better than commercially made ones, in
fact. It exercises the tubes under actual working conditions, and meters
the results for you to observe.
- Notice how much drive is
available. A fresh 12BY7A will provide more drive than
necessary to swing the ALC Meter through its range, even on 10M. Low
drive on any band shows that the driver tube is probably falling off in
emission. It will continue to function for a while, but you might
consider replacing it in the near future.
- Watch for falling drive level as the rig is keyed for
a few seconds. A 12BY7A near the end of its life will fall
off in drive within a few seconds or so of key-down. If you
see your drive fall as you are watching, that tube is positively ready for
- Check the sharpness of the dip in CW
Mode. A broad, shallow dip means the finals are nearing the
end. You will notice reduced power output as well, most
noticeable on the higher bands.
- Check for falling plate current under key down
conditions. Just like the driver tube, final tubes at the
end of their useful life will jump to full Ip
and then quickly start falling off. When you spot
this, they are ready for recycling.
A Few Notes Related to Output Power
The difference between 50W and 100W is 3db. An
S-unit is 6db. Consequently, the difference between a 50W rig and a
100W rig at the receiving end is about 1/2 S-unit. The difference
between 90W and 100W rigs is not even discernable at the other end.
Likewise between 100W and 110W. Resist the urge to load up your rig "To
The Max," as all it does is shorten the life of most everything in the final
section of your hybrid.
A reasonable increase in power, the first step really
worth taking, is times ten. This holds for audio amps, HF amps, heck, for
most all amps! The difference between 100W and 1,000W is 10db.
That is about 1-1/2+ S-units at the receiving end, and is indeed
noticeable. About the same as going from a poor antenna to a good
The HV position of the meter reads the plate voltage
applied to the finals. The Kenwood hybrids utilize a voltage doubler
circuit in the HV power supply, and aging High Voltage capacitors can result in
low output. To check for this possibility, monitor the HV as you key the
rig. It is normal to see perhaps 10% drop in HV when keyed. Anything
much in excess of this might indicate failing