Hi,

I would think that you would use a 3 amp fuse if wired for 220V,
6A for 110V (I don't have a Kenwood manual to check this,
but a 6 amp fuse sounds right at 110V).

First check your resting plate current before tuning up.
With PTT set to transmit, and no drive/no audio,
the finals should draw about 40mA plate current.
If not, adjust the bias control for this reading.

The proper way to dip a pi net final is to start with the loading
capacitor fully meshed. Apply some drive and quickly dip the final
plate current using the plate tune control only.

Then apply full drive* (see note) and read the plate current
(it should be much less than the rated 250 mA).
Assuming it is less than the desired 250mA,
increase the loading control slightly
(say, enough to result in a 20 mA increase in plate current
with full drive)and then quickly redip
using the plate tuning control.
(+Always+ redip with the tuning control last,
or you will be operating with your final out of resonance).
Note that you are always dipping with full drive applied.

Note that you can dip the final using the plate tune control
while less than full drive is applied (easier on the tubes),
but you then must increase the drive to full drive to see
if you have reached 250mA plate current at dip
with full drive, which is your goal.

Continue this procedure until either the rf power output
no longer increases when you increase the load control
with drive,
or you have reached 250mA plate current at dip with full drive,
whichever comes first. Do not operate with more than
250mA plate current at dip, full drive, or you will overheat
your finals.

*Note: By "full drive", I mean enough drive for the plate current
to stop increasing very much with increasing drive (saturated),
not that the drive control is fully clockwise.

If you don't get around 100W rf out at 250mA dipped plate current,
one possibility is that the final tubes are not well balanced.
With the bias set for 40mA with both finals installed,
if you remove one, the resting current should be 20mA.
If the tubes aren't well balanced, one tube may be hogging
all the current, and the rig will be unable to deliver more than
about 50 or 60 Watts. Note: remove one of the tubes
completely for this check, do not just remove the plate connector
of the unused tube, or it may be damaged by excessive screen current
(the screen tries to act like the plate). Caution: high voltage
at plate caps of the 6146's - keep one hand in your pocket
when you poke around near the final cage. Use a shorting stick
before touching the plate cap.

To check neutralization, you transmit with no drive,
PTT on, no audio, (i.e., same set-up as 40 mA bias check),
and with the loading capacitor fully meshed, you rock
the plate tuning capacitor throughout its full range.
The plate current meter should remain at 40mA.
Any sudden, drastic increase as you vary the plate tune
capacitor with no drive in this manner indicates
a neutralization problem. Note: this can be a destructive
test, as the onset of a parasitic oscillation can be sudden,
with very high plate current. Be ready to turn off
the final quickly. A dummy load is best for this test,
rather than an antenna.

73,
Ed Knobloch


Gary wrote:
I bought a TS-830 from a ham friend that buys estates etc. He couldn't
get more than 30 watts out of the '830. I tried it and by putting the
drive control at a low level then dipping the plates and adjusting the
load control and finally increasing the drive control I was able to
get 100 watts out. Then the rig went dead. I checked the fuse on the
back and it was blown. It was a 3 amp fuse but right underneath the
fuse holder in white lettering it said 6A I'm wondering if the '830
should have a 6 amp fuse instead of the 3 amp fuse that was in there ?

Also I noticed that even when the plates were dipped correctly that
the plate current meter at 100 W out was almost pinned to the max,
maybe it needs neutralization ?

Thanks in advance.

Gary