I recently completed restoring a pair of S-40B radios. The original
power transformers were pretty marginal, so I replaced them with similar
transformers that I bought from Antique Electronic Supply (the new
xfrmrs were Fender amp replacements). Everything seemed to work ok for
a couple of weeks of light use of my radio (I gave the other to my father).

Last week while I was listening to my S-40B, its power supply blew a
fuse (a 5A cartridge fuse that I installed in the radio). I traced the
problem back to the "new" power transformer. It appeared to have a
short circuit of some kind, though I could never pin down exactly where
this short was using a DVM.

The initial fuse blow occurred while the radio was running and my
house's central air conditioner was switching on. Up to that first fuse
blow, I noticed some significant flicker in the dial lamps (run off the
filament winding on the power transformer). At first I thought that I
was watching a dying lamp bulb, but now it seems that I was witnessing
the breakdown of the power transformer.

My question is, would installing an inrush current protector thermistor
in the primary winding circuit of this radio prevent a repeat of the
transformer breakdown? If this is a good move, what size of thermistor
should I use? Any help or recommendations would be appreciated.

Steve Burrows