Anyone recommend what bench power supply I should get?

[Crush]

Hi!

I've asked on several other forums and no one knows the answer so I'll try here.

-I would like to make tube amps and pedals as a hobby. I have no interest in transistors amps at all.
-I'm a 'tone head' would like to play around with eq's and different things like low high/low pass filters.
-I would like to use a breadboard so I can interchange components easily.
-I do not want to build my own power supply unless I really had to or the cost of buying one was prohibitive.

I simply would like to know which type and strength of bench power supply I would need for the tasks listed above or how to power the amp circuit on the breadboard like I see in Youtube videos.

I have tried 3 different electronic forums and people basically did not know the answer to the question as they seem to be more into playing with LED's and Arduino's and such.

I thought I would ask here and hopefully get a recommendation of what I should buy for my bench/lab setup.

[loudthud]

Look for a Heathkit IP-32 or IP-17 on Ebay. They put out 0-400V at 100mA and have a heater supply. You should re-cap them. They use a pair of 6L6 tubes for the high voltage. They are ok for preamps and very small power amps. If you want to go bigger, look for something like 500V at 500mA. I have one that uses five 7581 tubes in parallel. Another boat anchor I have uses six 6L6 tubes. It has choke filtered power and a variac ganged with the voltage adjust pot. Weighs a lot!

[Enzo]

I have a collection of them. I have one each of those two Heath models. They work fine for small projects. Preamps certainly, and power amps are limited by the 100ma top. But it is enough for at least smaller power amps and intitial testing. So I agree with Loudthud.

Those include a 0-100 volt negative supply for bias too.

I also have several electrophoresis supplies. They generate something like 0-500vDC at I am not sure what currents, though the meters go well over 100ma. Intertesting to me is that some of them use a small variac inside to run the high voltage transformer. That gets it variable. Those of course have no heater supply. Nor a negative supply for bias. But one needs no bias supply for most preamp designs. And having a separate 6v transformer is no problem in my shop.

If you want to make a preamp, and you are (likely) using 12AX7s, then my rule of thumb for high voltage is about a milliamp per triode. Three tube is six triodes, so about 6ma, then double that. We still are only at 12ma, which just about any power supply you can imagine will handle with ease. SO no problem covering that. High voltage for a power amp means adding to the preamp all the power the output stage needs, including its phase inverter. SO a few more ma for the PI, then and how much power do you plan to design for?

heater supply is easy, add up the tubes. At 6v, 12AX7 and similar want 0.3A each, 6L6s want 0.9A each, EL34s 1.5A each. Look up any others you use. What is the largest tube count that you intend to design for? Add them up.

Bias supplies are easy, there will usually be no current demand at all. 10ma is plenty.


I also have several low voltage bench supplies, most are dual 0-20 or 0-30vDC variables, plus a +5. They are great for solid state work, and yes, the supplies useful for tube work and the ones useful for solid state work really are not much use to each other.

You can look on ebay to see what those Heath models are selling for, I have no idea. If I decided to sell any of mine, I wouldn't give them away. But I don;t know what your price threshold is before you decide to just make one.

[Steve Conner]

All good advice. I don't think anyone makes bench power supplies suitable for tube circuits any more, so those old Heathkit-type supplies aren't just your best bet, they're your only bet.

Well, almost. I used to have a huge, heavy old one full of tubes with plate caps, but I had to junk it because I needed the space. I replaced it with a Xantrex switchmode power supply that puts out 0-600V at 1.6 amps, the same 19" rack footprint, but only 1U tall instead of 5. I also picked up the 0-150V, 6 amp version, and several of the ordinary low-voltage kind, so I'm sorted for just about any tube or solid-state situation.

I must admit that if I only worked with tubes, I wouldn't have gone for this setup, but I also like to tinker with solid-state power electronics and often have a need for a high-current supply at 160 or 320V.

The switchmode power supplies are electrically noisy, but it's never caused me any trouble in test bench work (yet ) When testing preamp circuits I add an extra RC filter to the supply rail. This would be present in the final application anyway.

Electrophoresis power supplies are switchmode too nowadays, I've seen them with huge outputs in a tiny package.

[Enzo]

All the old electrophoresis supplies I have are plain vanilla linear supplies. I mentioned some of them have a small variac powering the transformer inside to make the thing adjustable. Works fine, but oh so less sophisticated than SMPS.

[Zozobra]

I suppose you could always build one and I guess it wouldn't be a bad little community project.
Take a PT like the antek AN-4T400 which has all the HT and heater current you'll ever need and it'll run up to 560V after rectification and it only costs $50.
Give it a good dose of reservoir filtering and pull a bias rail off it too.
Stick a VVR circuit on after the filter and perhaps stick on a capacitor multiplier filter afterwards to get a nice smooth DC output.
Stick on a panel volt meter to measure the output.
Use a bunch of military/amphenol connectors on the front panel to safely get the power out to where you want it.

You'd have a bench supply that could service 100W+ amps for perhaps $100.

[Steve Conner]

I can see it costing a good deal more than that once you've bought a chassis, filter capacitors, heatsinks, meters and so on. Also the VVR circuit isn't short-circuit proof: it's pretty non-trivial to make a solid-state high voltage regulator that is. I've done it, but I used some pretty aggressive foldback. The rated output current was 300mA, but the short-circuit current was only about 50mA.

[Zozobra]

Just thinking out loud My experience is somewhat limited with this sort of stuff. I'm going pretty much off Merlins power supply book truth be told and I dan't have that in front of me.
As a better than nothing could you not perhaps add current limiting to the cap multiplier to drop the HT in the even of a short and accept that thing isn't fool proof and if you bodge the wiring elsewhere it will go poof?

[Steve Conner]

Well, for me, a big attraction of bench power supplies is that they have a variable current limit, and you can bring a new unknown circuit up carefully in the knowledge that nothing bad will happen if it shorts out. Instead of a small explosion and fire you just get a blinking Current Limit LED.

The old tube-regulated power supplies have a natural current limit because the tubes can only pass so much current. If you left one shorted for a long time, the tubes might overheat, but it wouldn't blow up instantly like a solid-state regulator can.

Having volt and amp meters is nice too.

[Zozobra]

All good points!