"Steven P. Burrows" wrote in message
news:461mg.57866$9c6.34117@dukeread11...
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
Steve,
When I was a Novice, I used a S-40B on 80-40-15 meters CW. Boy, 15 meters
CW was a challenge with that primitive receiver! They did a good job with AM
broadcast however, and the audio was decent.
Now the bad news. Maybe your rectifier tube showed a series of bright
sparks leading to the blown fuse? If so, the B+ was being dragged down
somewhere, and likely from a leaky, or shorted capacitor. It's quick and
easy to pull the rectifier (5Y3??) and see if the fuse blows again. A 5
ampere fuse is pretty heavy for a S-40B, so in the future consider a 2 amp
unit. If there was no short, or bad 5Y3, then your new transformer was
likely marginal, and I bet would have failed regardless of what you did.
That said, if large transients come down the power line, you can filter
these out to a point. One option is to add a varistor across the primary
leads of the transformer. These are made by GE and others, and the part
number will be similar to V130LA10A. This means the part is rated for 130
volts RMS AC, and 10 Joule rated. I believe Radio Shack has these.
I don't believe an inrush current limiter is a solution here. These are more
useful when a big light dimming surge occurs when turning on a big Linear
amplifier like the Dentron MLA-2500.
Good luck with that S-40B,
Jim
WD5JKO