[Boatanchors] Repair of B&W Tank Circuit

Mon, 26 Apr 2004 19:51:23 -0400

Mike,

That sounds like an interesting project.  I have a couple of thoughts.

1.  If it is a "standard" B&W tank coil, a replacement can be had if one
searches the boneyards and keeps up with all the "for sale" places.  The
question is, which one?  850, 850A, 851, 852? I suspect that is an 850A..

2. B&W's manufacturing process affixed the coil to the ribs by heating the
wire..  Good process but I would guess that time and heat have reversed the
process!  From inspection of a 851 tank circuit, I believe that the taps
could be unsoldered, the coil removed and repaired and then re-assembled.
Since I build some air wound coils, I believe the coil could be repaired by
fabricating new ribs.  I make ribs from 3/8" Lexan sheets.  I cut 3/8" wide
strips, using a small bandsaw (fine tooth metal cutting blade) and a
homebrew fence (a piece of 1x2 and two C-Clamps).  I drill the strips, using
a small drill press and another homebrew jig (a fence with a stop at one
end) and spacers cut from various materials.  For instance, the 851 has 15
turns of AWG 12, with ribs, at 8 TPI.  So, my spacers would be cut from 1/8"
plywood.  I get everything lined up, drill the first hole, remove a spacer,
reposition the work, drill the next hole and repeat the process untill I am
done.  In this case, since there are 15 turns, I would drill 16 holes.  For
AWG 12, I use a 7/64 drill bit with a 135 degree tip. And, I generally tape
two ribs together and drill them at the same time.  The drill press would
drill all four but I have more trouble with heat and melting the stock..
After the ribs are drilled and cleaned up a bit, I sit down and thread the
coil onto the ribs, one hole at a time.  When I finish that, I make sure the
ribs are positioned correctly and then I run a bead of glue (I use model
airplane glue) along each rib where the wire comes through.  The glue
"stiffens" the coil assembly. And, I guess I should mention that I would cut
the ribs extra long, in the beginning.  You can always trim them, with the
bandsaw, and cut the mounting points with a good hacksaw, etc..

Does that help?

73,

Larry
KQ4BY

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Mike Clarson
Sent: Monday, April 26, 2004 6:23 PM
To: [email protected]
Subject: [Boatanchors] Repair of B&W Tank Circuit

Gentlemen: I have recently aquired a B&W LPA-1 "Widowmaker" linear
amplifier. No interlocks, plenty of exposed HV under the easy to open cover,
and, just for fun, exposed 120 volt terminals on the back of the power
supply. 4 866s powering 2 813s. The tank coil used to have plastic keeping
it rigid, however, this palstic has turned to some grey shards of some other
flakey substance. It is one of the standard B&W tank circuits with the
switch. Has anyone referbished one of these tanks and repaired the coil? I
am open to suggestions before attempting trial and error repair
mysef. --Mike, WV2ZOW

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