This is one of my old battery chargers, the selenium rectifier went bad and started to internally short out.
Replacing selenium rectifiers with silicon diodes is not recommended on non-short protected battery chargers, as the selenium rectifiers have an internal resistance that acts as a current limit on short circuits. In this case the secondary side is proteced and I’ll try not to short it out.
I replaced the selenium rectifier with a beefy bridge rectifier and also made a small heatsink out of sheet metal to get the temperature of it a little down into nominal operating range.
