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June 21st 06, 03:41 AM
posted to rec.radio.amateur.boatanchors
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Inrush Current Limiter for Hallicrafters S-40B?
"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 |
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