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Title: Help with a Heathkit SB101 power supply Post by: K8DI on March 05, 2020, 04:59:42 PM I picked up a Heathkit SB101 and it’s external power supply last week. The supply rattled.... as you can see in the photo, a resistor was blown up and one half was loose. I cannot tell exactly where it’s supposed to be. There’s not an obvious ‘place it was’ mark nearby. I suspect it was to a ground lug on the capacitor (other caps have paralleled bleeders). Anyone know for sure?
Title: Re: Help with a Heathkit SB101 power supply Post by: KK4YY on March 05, 2020, 05:26:42 PM Lookup the schematic of your power supply here:
https://www.vintage-radio.info/heathkit/ (https://www.vintage-radio.info/heathkit/) Title: Re: Help with a Heathkit SB101 power supply Post by: K8DI on March 05, 2020, 05:53:27 PM Lookup the schematic of your power supply here: https://www.vintage-radio.info/heathkit/ (https://www.vintage-radio.info/heathkit/) Thanks for the link! Found the schematic, verified it is a bleeder that goes to chassis. Now to replace that, add a fuse holder, and a grounded power cord. If I can find room inside the chassis, a relay and separate power supply for it instead of running 120vac to the radio power switch, as well. Then I will see if the radio itself is parts or a restoration.... Thanks, Ed Title: Re: Help with a Heathkit SB101 power supply Post by: KK4YY on March 05, 2020, 07:34:21 PM Ed,
The resistors that didn't burn up may have drifted in value. Best to check them, at the very least. Those 2 watt carbon composition resistors are dissipating almost 1.7 watts each. This might be a good time to replace them all with 5 watt metal oxide film resistors (or better). Those Heathkit power supplies are still in good demand. I bought a couple of their DC to DC supplies. With new caps and diodes they're as good as new. Don Title: Re: Help with a Heathkit SB101 power supply Post by: K8DI on March 05, 2020, 08:25:02 PM The resistors that didn't burn up may have drifted in value. I'm sure they have. Caps are probably dried out too... But first I'm going to see if the radio is restoration-worthy before I fully rebuild the power supply...I only need it to nominally work enough to bring the radio up on a variac to get some idea of its condition. Ed Title: Re: Help with a Heathkit SB101 power supply Post by: nq5t on March 05, 2020, 08:48:14 PM The resistors that didn't burn up may have drifted in value. I'm sure they have. Caps are probably dried out too... But first I'm going to see if the radio is restoration-worthy before I fully rebuild the power supply...I only need it to nominally work enough to bring the radio up on a variac to get some idea of its condition. Ed You should probably consider one of these. Easier than trying to do a one-piece at a time upgrade. Excellent product …..https://www.theheathkitshop.com/page16/index.html |