Kenwood
Hybrid Tune-Up Procedure
by
Ken, K4EAA
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 ALC
- 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
again.
- 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
well.
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
RTTY
- 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.
You're
almost 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 point.
- 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
meter.
- Try adjusting the Load
up or down a bit, re-peaking with the Plate tuning
after every adjustment.
- 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 excessive
compression.
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 retirement.
- 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 antenna.
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
capacitors.
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All Photos and content copyright 2005, 2006 K4EAA, Ken
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