What to do with 700VA 10-0-10 transformer?

[Lingwendil]

Hello, I was given six 700VA 20V(center tapped) transformers a while back, other than Beefy low voltage PSU's, what else could I use them for? They weigh a good 10 pounds each, and have a 120/240v primary, so I can run them back to back for a high voltage supply, but their size makes that somewhat cumbersome. I was considering using them as output transformers for a Push-pull tube output stage, assuming my calculatins are correct, wired for 120-0-120 primary, 10-0-10 secondary, that would give them an impedance ratio of 1152 ohms plate to plate? What would be some tubes to experiment with? Seven el84 in parallel on either side, fourteen per channel sounds like a worthy experiment, but I unfortunately don't have that many el84! Rewinding is out of the question. Any ideas?

 

[Iain McNeill]

If they're mains power transformers then they'll only be good at 50/60 Hz. They'll have a horrible bandwidth/frequency response.

Biggest opportunity is in solar power & 12V battery storage & inverters up to 50/60Hz. Do a nice pure sine 12V to 120V conversion with an efficient class D output.

 

[pheonix358]

Perfect for running 10W Leds. One would provide enough to wire your whole house to LED lighting. I suggest you sell most of them and make up a real +/- 12v power supply. Also would run a whole bank of class D amps on 28v single supply.

Terry

 

[Lingwendil]

Perfect for running 10W Leds. One would provide enough to wire your whole house to LED lighting. I suggest you sell most of them and make up a real +/- 12v power supply. Also would run a whole bank of class D amps on 28v single supply.

Terry

Hmmm, class D home theater supply? Might be my best bet...

 

[pheonix358]

Put some of them up on Swap meet. If you were not in the USA I would be the first buyer. I would love a couple of them! Oh well, such is life! Postage costs is such a pain.

Terry

 

[gmphadte]

May be u can use one to convert mains voltage from one to another for something.
Connect the secondaries in series and get the multiple of 10 volts for an Amp.

 

[kavermei]

Make an electrostatic loudspeaker around them, this works excellent with mains toroids.

Toroids are not half bad for tube OPT service. But they are less tolerant to DC imbalance compared to EI trannies so make sure you can trim this in your amp. You could use one half of the secondary to get 4x the primary impedance and increase the number of tube candidates. Or you could try oddball tubes with very low rp, like the 6as7.

 

[Lingwendil]

They're conventional transformers, so the DC might not be an issue. If I had some 6as7's I'd try them with these trannies.

 

[Jonathan Bright]

I'm not an expert at this but I think you can wire the secondaries to get 20+20* by configuring them as voltage doublers. Look it up on the Net but you'll find its only the way the diodes are connected. Now you'll find that the frequency of the secondary voltage goes from 100/120 c/s to 50/60 c/s. But that is not a huge problem. With 20+20 you can make some serious Class A power amps. 8 or 4 ohms.

Edit: *or you might actually get a bit more voltage. (Sorry can't remember the exact formula.)

 

[Luke]

aleph-x sounds ideal for two of these tx's

 

[kavermei]

I'm not an expert at this but I think you can wire the secondaries to get 20+20* by configuring them as voltage doublers. Look it up on the Net but you'll find its only the way the diodes are connected. Now you'll find that the frequency of the secondary voltage goes from 100/120 c/s to 50/60 c/s. But that is not a huge problem. With 20+20 you can make some serious Class A power amps. 8 or 4 ohms.

You're right, but doublers tend to have poor regulation and a lot of ripple. A regulator would be needed to get a decent result.

Someone suggested using two and chaining up the secondaries; this would be a better option were it not for the hugeness of the result (remember, these are 700VA units ).

A slightly more adventurous option would be to rewind the secondaries. On a toroid, this actually sounds harder than it is

 

[AndrewT]

35A through each secondary demands a lot of copper cross sectional area.
Find out if the secondaries are wound bi-fillar or tri-fillar or quad-fillar.
Separate the joints and identify the separate windings. Connect them in series to give a more useful voltage and current combination.

I had a 500VA 25V toroid. I opened it up to find tri-fillar. Adding one more winding gave me a 25+25+25+25Vac 500VA transformer.

 

[Lingwendil]

I'm not an expert at this but I think you can wire the secondaries to get 20+20* by configuring them as voltage doublers. Look it up on the Net but you'll find its only the way the diodes are connected. Now you'll find that the frequency of the secondary voltage goes from 100/120 c/s to 50/60 c/s. But that is not a huge problem. With 20+20 you can make some serious Class A power amps. 8 or 4 ohms.

Edit: *or you might actually get a bit more voltage. (Sorry can't remember the exact formula.)

As of this moment I'm building a class A Szekeres mosfet buffer with one of them, voltage doubled to give me around 32~36v after regulation, 1.08A per channel with an LM317T CCS. I've built high power buffers like this before, but these will be the first to use a common power transformer, and also the first to go over 18V supply. I figure that If I have these guys I might as well use one or two, and maybe sell the rest when I can.

 

[dave_gerecke]

I would have to give a second to the idea of using these in an aleph, or a First Watt or Zen series amp. That's right it the correct voltage region, and quite a healthy VA rating.

Peace,

Dave

P.S. If you do sell some of them, I might be interested!

 

[Lingwendil]

I would have to give a second to the idea of using these in an aleph, or a First Watt or Zen series amp. That's right it the correct voltage region, and quite a healthy VA rating.

Peace,

Dave

P.S. If you do sell some of them, I might be interested!

maybe, btw, what state are you in, I'm contemplating selling a couple, just getting a feel for shipping. What would be a reasonable price for these trannies?