Bob -
This is typical deterioration of the PA tubes. Certainly there are
other possible causes such as a weak Driver tube and myriad other
'possibilities'. But most often it's PA tubes.
If subbing new tubes in the PA and/or Driver does NOT result in full
power, then it's time to investigate further. Start by checking
voltages, especially in the PA. Screen and Cathode voltages are
particularly important and should be nearly equal on both tubes.
It's also possible that the alignment of the Driver stage has
'slipped'. These trimmers are often at or near minimum capacitance,
resulting in little or no tension on the adjustment. Vibration,
mechanical shock, temperature excursions etc., can all disturb these
adjustments. They are very 'sharp', so very little movement will
drastically affect the output power. I always 'seal' the two top bands
with a little clear nail polish to help hold them where they belong.
CAUTION! Do not use an uninsulated alignment tool on the trimmer caps.
Even a momentary short to the chassis will destroy R44.
If still no luck, check back!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Robert Fish wrote:
Hi Guys,
I was up checking out activity on 17 meters today. There wasn't much.
Surprise surprise, but it reminded me of a problem my T-4XC has. I
have been ignoring this issue for
a while now because the bands have been so dead. I tuned up the
transmitter so I could call CQ on 17 meters today and I barely got 60
watts out. On 10 meters, it's more like
50 watts. It is any band that uses those two band switch positions
21.0 and 28.5 MHZ.
I get over 100 watts on all the other bands, quite a bit more than a
hundred on 80 meters.
I suppose I could tune her up on 40 meters and then write down some
power levels at various places along the transmit chain and then go
back and do it on 10 or 15 meters and
narrow it down to a section that way. I would expect the higher bands
to be somewhat lower power, but not that much, or am I wrong. Is there
anyplace I should start looking.
Thanks & 73,
Bob K6GGO
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