Modifying Plate Transformers' Secondary Voltage

[doorunrun]

Hello All,

Years ago I worked with a ham radio operator who told me how he modified power transformers to meet certain voltage requirements.

I can't remember the exact details, but I think it had something to do with finding out the turns ratio between primary and secondary. Disassembling the transformer and remove/add turns as needed to arrive at the desired voltage transformation.

Searching around for a video or detailed description of the process I haven't been able to find any that click. Maybe I'm searching with the wrong terms.
Is this a lost art?

I'm hoping maybe someone here has been there and done it.

I have a plate/filament transformer from an old tube console stereo that has a 630V C.T. secondary. I'd like to modify it to build a 220-250V linear supply for the 3 tube Ribbon Mic PreAmp I've been working on.

Thanks!

 

[Philbo King]

I've never delved into modifying pwr transformers. But if a current system uses tube rectifiers, converting it to use solid state diodes can boost the DC output voltage significantly.

 

[CJ]

You would have to delaminate the core, this can bend up the lams pretty good unless it has a less than normal varnish job.

Then you would strip off the secondary and buy some copper wire to rewind the secondary. Then you have to buy garnish (I mean varnish, funny spellchecker Inserrt)and a toaster oven and rebake outside somewhere away from humans and wildlife.

At this point it becomes much easier to buy a new xfmr. A used one is cheap on evilbay and you will save a ton of time and headache and possibly a house fire.

Oh. And you need to build a winding machine. With a turns counter.

In the time it takes to do this and maybe do it twice you could get a 4 year degree and raise up a family of 5.

 

[emrr]

You need to look at the various ways you can do the rectification and how that affects the voltage, expected load, predicted load in the original location. Series step down resistors in the smoothing section to lower B+. Then there's potential regulation methods. Rewinding a transformer sounds pretty much cart before the horse.

Filament voltage, if you intend to use that, is probably the bigger issue. You may need something different for that alone.

There are definitely plenty of old magazine articles about how to repurpose/rewind power transformers, many online. The usual 50's DIY electronics mags.