Paul -
Since you have rebuilt the power supply, we'll assume the Bias supply is
stable. Most likely cause is a gassy tube in V19, a 6EV7. One other
possibility is R106 (3.3M, 1/2W) gone up in value due to age. R106 is
right on the top edge of the small pc board under the chassis right
beside the V19 socket. If neither of these, may need further investigation.
C145 is another possible cause for the VOX hanging, although further
down the list. A replacement "may" be available from Tom at
<www.hayseedhamfest.com>
He is having some supplier problems currently and I don't know what he
has in stock, but that is a cap he offers.
There are several fan options. Simplest is a small 120V AC fan with
rubber bumper feet at the corners, lying on top of the cabinet over the
PA. some have used a surplus fan for 230V AC and run it at reduced
speed from 120V AC. A small computer fan (usually 12V DC) can be
mounted similarly and run from a wall wart. Some have tapped the
filament line inside the transmitter, a silicon diode, and electrolytic
to run a computer fan. Either type of fan can be mounted on the rear
wall of the PA enclosure using existing holes. You do NOT need a gale
force wind from the fan. Just a gently breeze, blowing _OUT_ to move
the heated air away from the PA cage.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Paul Strickland wrote:
I acquired this TR-4C from my father a decade ago, W9LKZ (SK). I've
rebuild the power supply with great success a few years ago. Now I
have a problem with the xmtr keying circuit. After allowing the rig
to warm up for half an hour or so when I key the mic and then release
it the transmitter section remains in the transmit mode. Not a whole
lot of fun... I also found this 4 section cap # C145. Where can I
find a replacement for this device. I love these old glow in the dark
rigs, also keeps the shack warm in the winter. I have also seen/heard
of a mod to put a fan over the final amp cage. What voltage is being
used to power the fan and how big of a fan?
Thanks for all the other good info I've gleaned from this site
Paul Strickland
WB9SUG
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