PSU Voltage Surges

Yes it probably didn't matter then. Tubes don't suddenly go short circuit anode to cathode if you over stress them a little for a short time.

A simple timer, relay and loading resistor might work.

We had a Heathkit tube bench supply that did that at turnon. It blew up transistor circuits.

You could hang a big MOV or TVS across your load circuit.

Or put a time delay relay inside the supply. Or a pushbutton enable.

Or buy a new power supply!

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

What Edward Rawde said will work. Another option: a resistor in series on AC input, switched out of circuit after delay. That has an advantage of being a little bit gentler on the transformer, diodes and B+ caps.

Ed

My Farnell power supply also does that. There are two switches, one for the mains and one for the HT output. You just keep the output switched off until the voltage has had time to settle down.

Might be the same supply if it's the 350V one by the sound of it; that's a Farnell as well. It has 6 ranges, course and fine controls, mA & V moving coil meters and a bunch of fixed low voltage outputs for heaters and stuff. Same as yours? I'm not mad keen on your solution, though. I tend to be rather absent minded!

It's not doing the heaters in the tubes I'm testing any favors either, as the low votage PSU is the one I'm using for that section of the test rig.

Not sure they'd be any good for longer duration surges as these are (~4 seconds)

No, if I did that I'd have to junk the existing ones to make space and I'm not about to do that with supplies that are in all other respects, very good indeed and will probably still be around for many more years than the new replacement would be!

The timer idea put forward by you and Edward is the frontrunner so far.

Measure the short-circuit current at turnon, and see what you have to deal with. If the tubes are just warming up, it may be low.

Power supply turnon and sequencing are still an issue in the 21st century.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Almost every second order control loop gives a ringing response to a disturbance - you can configure them to be critically damped, where there only a very small overshoot, or over-damped where there isn't any, but then the output tends to take quite a while to get up to it's stable level.

Yes, that's it. The series stabiliser is two EL34 valves in parallel and it has a very clever circuit for keeping them within their safe operating area.

Think of the HT switch as "Default Off" and only switch it on when you are ready to do a test - then switch it straight off again. Absent minded and working with high voltages can be a dangerous combination.

Take care!

How about a pushbutton that muat be pushed once after powerup? It could even light up to remind you to push it.

For extra credit, use a tube (valve) circuit.

Schematics could be posted here. I might remember how to design tube circuits.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

The issue is probably nasty states caused by tubes heating up in the wrong order.

See the book Genius by James Gleick.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Yeah, I can see where you're coming from here. Not a bad idea at all. I might adopt that.

Actually, all you need is a dpdt relay and a pushbutton.

Too easy, no fun.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Yeah, well, I've been goofing around with EHT stuff for more decades now than I care to admit to so I must have *some* level of self-preservation in my method! Let me get this right: if I use your method and just switch the HT switch on/off for testing, I won't see any surge? I have *so* much old vintage test gear I simply cannot be thoroughly familiar with every single piece of it; no one could. Anyway, you're saying just toggle the HT on and off once the main deal has warmed up? If so, that might work with my Solartron HV PSU too, since that uses a similar system. :-/

Or so John Larkin wants to tell us. Citing a book called "Genius" doesn't make you one.

Finding relays rated for high voltages takes a bit of an effort, and getting an arc between the contacts can wreck them.

I found one rated for 30kV stand-off once, but it still wouldn't do what we wanted it to do. Pity - for once the circuit operation would have been easy to explain.

I think that is how the Farnell PSU is intended to be used. The HT switch is in the output circuit and just breaks the connection to the front panel terminals.

Because the main high voltage supply uses semiconductor rectifiers, it rises to peak value the moment the equipment is switched on, before the regulator valves have warmed up. At that stage the output voltage is determined by various incidental current paths through the sensing resistor chain and tends to drift up to just above the maximum setting of the selected voltage range. As the regulator valves warm up and take control, the voltage comes back to what it should be.

It is not a good idea to keep switching valve equipment on and off - but equally, the experimenter doesn't want to work on his 'rats-nest' while parts of it are live. The HT switch removes the need to keep switching the whole instrument on and off, the regulator valves can be left running and the HT can be switched on and off without a surge or any warm-up delay.

It only has to close on high voltage, not open.

That's easy.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

OK, don't read it. I can see why you wouldn't want to.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics