[R-390] Potting tar in power transformer

[AI2Q]

Absolutely right on Steve.

I recently repaired a primary-to-secondary short in a HV xfmr for a 
Heathklit SB-220 kw amplifier. Removal of the end bells revealed the 
breakdown in insulation, and that the windings themslves weren't burned 
open. A thorougf cleaniung, followed by an application of galss tape and 
fish paper did the trick.

Vy 73, AI2Q, Alex in Maine
ARRL, FOC 1861, AWA, QRP-L 687
http://users.adelphia.net/~alexmm/ai2q.htm

----- Original Message ----- 
From: Steve Hobensack
To: r-390 at mailman.qth.net
Sent: Monday, May 28, 2007 3:47 PM
Subject: [R-390] Potting tar in power transformer



  I just finished repairing my '63 Imperial. It was blowing the Mains fuse.
I got a bad megger reading on the dual 120 volt windings. Seems the potting
tar carbonized and shorted the power leads just inside the steel box. Five
years ago this happened with the high tension winding. I never thought it
would happen on the lower voltages. The repair is a little messy involving a
heat gun but straight forward. Just run some good teflon wire through the
porcelain bushings and don't use the attached solder lug. The power
transformer was marked "Phoenix company". In a nutshell , don't trash your
power transformer without first checking for insulation leakage.
..73..Steve..N8YE