Repairing Old School Power Supply?

[mattthemuppet]

I’ve only had one brush in 30 years it’s had 5 new handles and 18 new heads ( can’t remember the amounts, 2 Ronnies sketch very funny, of fork handles fame)
https://youtu.be/pV1IP4N9ajg
I’d hazard a rotted variac wire myself,
mark

I love that one too, had to go buy some "O"s the other day and thought of that sketch

[Jim Stewart]

Wow a selenium smoke generator!

Yeah. Maybe not many have seen them these days, but selenium rectifiers, if they burn up, produce seriously toxic smoke.

-js

[J Tiers]

That one from Rich C is a lot fancier than the OP's unit. Much of that fancy stuff probably is not present in the OP's.

[darryl]

In my first few years in the electronics business, selenium rectifiers were common. And they all smelled like farts. Sometimes I'd see them bridged with silicon rectifiers- then the voltage on the filter caps would be higher than normal, sometimes causing problems. I do not miss them at all.

If this plating power supply has them, it's probably safe to replace them with silicon rectifiers since you have some adjustability there anyway.

[psomero]

go buy an old used sorensen DCS on ebay. anything made in the last 30-40 years will be smaller, more efficient and more reliable than that thing

[J Tiers]

That would do it. Probably not more efficient though, it's hard to beat a transformer with a voltage dropping regulator system.

We need some pics of that old thang to see what's inside, just for curiosity if nothing else.

Why all the hate for selenium rectifiers? They work pretty well, and on a per-junction basis, they are fairly low-loss, comparable to silicon. It's only when you need a number of junctions that a silicon diode really beats them.

There now are better solutions for most useages, but they were very practical and inexpensive semiconductors at the time. They still can be for low voltages and high currents.

[PStechPaul]

Selenium rectifiers have a forward drop of about 1 volt per cell, and each cell can only withstand about 25 volts, so I don't see how they can be considered more efficient than silicon rectifiers. Germanium has even lower forward drop, as does Schottky. For the ultimate efficiency in low voltage rectification, active rectifiers constructed from MOSFETs are best.

[Georgineer]

At the risk of de-railing the thread, I've just discovered some instructions for building mains rectifier diodes from aluminium rod and lead sheet in 2 lb. jamjars of potassium phosphate solution. There are four of these arranged as a diode bridge, with carbon filament lamps used as volt droppers on the output. There's no attempt whatever to cover or insulate any of the terminals or wiring. Electrical safety? What's that?!

I've never heard of this chemistry being used to make a diode. Has anybody else ever come across it? It's in the Boy's Own Paper of August 1920 if anybody wants to look it up.

George

[Noitoen]

You can heat up some copper sheet to form a kind of scale on the surface to make a rudimentary solar cell

[J Tiers]

Selenium rectifiers have a forward drop of about 1 volt per cell, and each cell can only withstand about 25 volts, so I don't see how they can be considered more efficient than silicon rectifiers..............................

Not "more" efficient, but not significantly "less" efficient on a one-to-one basis junction-wise. Most silicon are theoretically 0.6v and in practical realization, have one volt forward voltage under load.

For any usage that has high current and low enough voltage to use a single junction, selenium can be practical enough. High current silicon diodes are not cheap.

Schottky and germanium are lower forward voltage, yes. Schottky are also high frequency, usually not used for bulk current usages, and germanium is not very popular these days for a host of reasons.

[mickeyf]

Why all the hate for selenium rectifiers?

I vaguely remember as a kid that the plates also had some photo-sensitivity, and could be used as a very low efficiency photocell. Scavenged from the back of defunct TVs.

[The Artful Bodger]

If it was a real antique DC power supply it would have a nice mercury arc rectifier!

[Noitoen]

I had a 12v battery charger with one of these

[The Artful Bodger]

Ah! The Tungar valve!

[Lee Cordochorea]

I have a need for such a thing now but I can't get any volts out of it, even when its plugged in!

Did you check the status of the fuse?