• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Alternative to Power Transformer

Just for your info.

Lambda make Isolating and Power factor correction front end modules which are pricey but probably not restrictively so.

The units take 85 to 265 V RMS input, 50 or 60 Hz, and produce 360V DC fully isolated outputs.

You can use that for the B+ and as the input for a further DC to DC Converter module to provide the heater supplies.

A very light weight power supply solution - just watch the thermal management issues.

The Units are:
PF1000A-360 (1000 Watt capability)
PF500A-260 (500 Watt capability)

There are also units which offer 280 Volt DC output.

Link to data sheets and application notes

They are NOT isolated. Here is one I took apart to repair after blowing it up. PF-1000A-360 They don't current limit either. Be prepared for smoke and fire. Everything is surface mounted on a metal sheet for heat sinking, and you have to heat the whole darn thing up with a blow torch to replace anything on it. I did get it working again though.

I use this for an isoation xfmr.:

but there are lots of similar industrial xfmrs on Epay.

Practically speaking, I think it is easier and cheaper to get a used PFC power supply model like a Kepco or Lambda off Epay and pull the PFC module out. They will be complete units too, the Lambda PF.... modules need energy storage capacitors, thermistor and a heatsink added yet. None of them are isolated though.

Another good one is the Vicor PFC module. That one might be isolated, not sure, I know something is different about it since it doesn't use a buck converter like the others. I have one I got surplus, but I haven't tried it out yet. The module is potted in solid plastic though, so no hope of repairing these if you blow one up.



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Oh Yeah,

I forgot to mention that you need to add an AC (UL approved) line input filter and another output filter on the DC with the Lambda PF.... modules.
Fortunately, the ones pulled from complete DC PFC supplies will have these included generally.

Another approach altogether is this cheapie ($5) little +/- 50V 1 Amp Lambda supply:

You have to redo the voltage regulation sensing so it monitors the +50V output instead of the +5V output. And it requires a minimum load current in order to regulate. I had this worked out once, but lost my paper work when I moved. So you are on your own on this one. But others have done it.

Connect several supplies in series for more B+ voltage up to 400V (max isolation rating). Conveniently gives you regulated 100V sub-multiples for front end circuitry too. (Make sure to draw the same current thru both + and - 50 V outputs since only the + 50V side is actively regulated.) Needs some better external AC line filtering and DC filtering too.

It seems I may have given bad advice.

I was aware that the VICOR front end modules were not isolated but the data sheet I have from the local supplier of the LAMBDA module says:
Input - Output: 3000V AC
Input - Baseplate: 2500V AC
Output - Baseplate: 500V AC

If its not isolated then off course it should not be used as a source of B+.