Just a few questions on upgrading my old linear power supply. I haven't touched electronics in years, I forgot quite a bit...
Schematic here:
Originally rated 0-30V/0-3A, I want it to go to 0-50V/0-5A.
The 'new, improved' power section consists of a 400VA toroid transformer, 35A bridge, 7400 uF 250 VDC filter capacitor, a TIP31C driving a bank of 5 parallel 2n3773 (with 0R22 emitter resistors) mounted on heatsinks with 110v fans at both ends. Following my first unsuccessful upgrade I fused the output to 5 amps to minimize fireworks.
The transformer supplies 53 VAC when both its secondary windings are connected in series. With this configuration the DC voltage at the collectors is 73.5 V *but* I'm currently using a single secondary winding giving me approx. 35 VDC output.
Will the circuit survive with 53 VAC on input? I'm asking this because I don't want the thing to blow up again like it did the first time when I was setting the max amp limit with 53 VAC. (Should have used a fuse!!) My first attempt at this upgrade involved adding 2 2n3055, they shorted out at about 4 amp.
It works great now with only half the supply voltage and I think it should work with full voltage because of the 2n3773s, though I'm a little unclear on the concept of 'secondary breakdown'. And I know the heatsinks may run a bit hotter but they're huge and well ventilated.
Thanks for all your comments.