Power supply current?

It would be helpful if you would list some of the valves numbers and how many valves you plan on operating at one time. Do not forget that you need the filiment voltage also. That could be 5, 6.3, 12.6, just to start with. You may need other voltages, but they are the most common.

The current for one valve could run from 50 to 200 ma.

Not yet decided! Bog standard AF triodes, probably.

Recommendations for suitable PSUs?

The chosen tube and power level and class of operation would be helpful. A visit to a "ham fest" or some such might yield a suitable PS. They call the old stuff - "boat anchors" because they are heavy.

I picked up a 0 - 1,000 Volt at one amp - For $15. I couldn't even buy the variac for that price. It was built by a master on a 19" rack panel, with metered output. I took out the ancient diodes put in some modern ones and put a filament transformer in the space it opened up.

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** If you are not competent to make yourself one - you need to think of another way to waste spare time.

BTW This has all the signs of being a stupid troll.

..... Phil

I'd love to. Please point me in the direction of a circuit diagram.

I guess you're new to the Internet? They have these things called "search engines" and all you gotta do is put a few words in, and it spits out sites that have what you want, links and all!

Your sarcasm is misplaced because there is no circuit diagram for a variable voltage power supply on that page.

"I wish to buy a power supply delivering up to 500V for experiments with thermionic valves. What would be a suitable current?" Where in that statement do you see variable supply?

I wish to buy wings so I can fly, what would be a suitable altitude?

You put a variable transformer on any of those PS and you have a variable output. Lot's easier than a solid state regulator and current limit operating at 500 V.

Dude, you are establishing yourself as a troll. Derision is warranted, sarcasm be damned. You seem to have no clear idea what you want, and that is pretty much where all designs start - a goal. Without a goal you are just wasting everyone's time.

Go to DIY Audio Projects and click on say "Mini Block Push-Pull EL84 (6BQ5) Valve Amplifiers" and just use the power supply part of the circuit.

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** You seem to be assuming something elaborate is needed.

FYI;

Such a DC supply does not need to be voltage regulated nor completely supply hum free.

The basic components required are a 120V/240V supply transformer with a 325V secondary, a bridge rectifier and 100uF, 500V electro.

Voltage variability is achieved with a Variac feeding the DC supply - readily available new or used and has a myriad of other uses.

Plus a source of 6.3V at a couple of amps.

..... Phil

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As others have pointed out, you need to be more specific. For example, if all you want to do is run a 12AX7/ECC83 double triode as a preamp, all you need is 250-300V at a few milliamps, plus 6.3 or 12.6V for the heater.

If you want to include a power amp, then you'll need a much beefier power supply.

Maybe you'd like to try this. I used it many many moons ago -

I need a variable voltage, say 100-500 volts.

Thank you.

Thank you. I'll feed it from a Variac (I have a Bronson) as Phil Allison suggested.

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** Using two transformers wired like that is a bad idea and will not do what you asked for. The seconds one will be driven into core saturation.

The better way is two identical, 240V to 50 or 60V trannies with windings in SERIES. So the combination is 100/120 to 480V.

Then a Variac drives the low voltage side to easily get 500VDC with NO saturation of any core.

... Phil

Don't use that circuit - see Phil's reply. And be aware of the capacitor voltage ratings. Using 400V filter caps in a 500V supply will destroy the caps.

Ed

The circuit is not intended to produce 500VDC which is not needed for, in the OP's words, "bog standard AF triodes". 500V far exceeds the maximum plate voltage of common AF triodes.

230:12 -> 12:230 transformation will theoretically output 230V AC which, after rectification and filtering cannot exceed 325V, less in practice. This was suggested for the OP to dabble with as a first step.

I used that configuration because small 6- and 12-volt transformers were easily available at local parts shops and, in fact, I had them in stock at that time. It worked.

How will 12V fed to a 12V winding (or 6V to 6V) saturate the core?

Better still would be a transformer with 350V and 6.3V/12.6V secondaries. But such trannies are probably hard to get these days and be quite expensive. Of course, if the OP still wants to go for a variable 500V supply, that's up to him.

Note to the OP: The two transformers are connected back-to-back. The low voltage output of the first transformer is fed to the low voltage winding of the second transformer. That is, what would normally be the secondary winding of the 2nd transformer is used as the primary.