anode cooler on the Thompson TH-308 type tubes
of the TH-308, TH-318, TH-328 and TH-338 tubes are very similar you may
want to swap the anode cooler on a tube from a 750 W cooler to a 1200 W
may want to remove the cooler in order to go for water
cooling by putting on a specially made water cooler on your tube. Mats,
KD5FZX, has done this on the GS23b tube, so it should be similar for the
is perfectly OK to do. Here is how to do it:
You start with this:
with removing the cover
plate on top of the tube using a small knife and a pair of pliers. The
captive screw can not be removed by itself, as it is designed only for tightening
and not for removing (non reciprocal grip). Lift the plate gently by
using the blade of the knife and insert the nose of the pliers and grip
the plate gentle but firm. Slowly rotate the plate counter-clockwise
and the screw will loosen. Remove the plate.
You will now see the heads of three hex-wrench screws. Loosen them by using a 2.5 mm hex wrench.
In order to remove the anode cooler (750 W) you can use a Gear
and Wheel Puller. I used a three arm one with locking of the arms.
by unscrewing the three hex screws for about 3 mm clearance to the
cooler. Adjust the arms of the puller for a good grip on the anode
cooler and lock them. Put a stiff plate on the heads of the screws (all
screw heads must be on the same level) and tighten the puller center
screw for contact with the stiff plate. The three hex-screws are now
only attached to the tube body and will push the tube body away from
the anode cooler. Now slowly continue to tighten the center screw of
the puller until the anode cooler releases from the tube body.
Unscrew the three hex-screws completely. Anode cooler is now free for the desired swop.
the desired cooler (1200 W) to the tube in question. Tighten the three
hex-screws firmly, but do over tighten them so the threads get
destroyed. Tighten them like you tighten the bolts on the wheels of
your car, soft at first and do round after round with all three screws
to get a proper tightening force. Put back the cover plate, but use a
new screw that is reciprocal for easy future removal.
Congratulation, you have now a higher power capability of your TH308, TH318 or TH328.
KD5FZX water cooling of GS23b: http://www.nd2x.net/kd5fzx-gs23H2O.html
Care and feeding of POWER GRID TUBES, Laboratory staff , Varian,
Eimac Division, 1967, Library of Congress No. 67-30070
Updated October 3rd, 2009.