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

Lingwendil · 17th September 2010, 01:27 AM

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 · 17th September 2010, 02:16 AM

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 · 17th September 2010, 02:24 AM

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 · 17th September 2010, 02:26 AM

Quote:

Originally Posted by 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

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

pheonix358 · 17th September 2010, 02:33 AM

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 · 17th September 2010, 04:02 AM

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 · 20th September 2010, 06:21 AM

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 · 20th September 2010, 07:13 AM

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 · 07:45 AM

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 · 20th September 2010, 07:46 AM

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

17th September 2010, 01:27 AM	#1
Lingwendil diyAudio Member Join Date: Apr 2008	What to do with 700VA 10-0-10 transformer? 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?

17th September 2010, 02:24 AM	#3
pheonix358 diyAudio Member Join Date: Jul 2008 Location: Stockport South Australia	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 __________________ What we don't understand is called magic.

17th September 2010, 02:33 AM	#5
pheonix358 diyAudio Member Join Date: Jul 2008 Location: Stockport South Australia	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 __________________ What we don't understand is called magic.

20th September 2010, 06:21 AM	#7
kavermei diyAudio Member Join Date: Jan 2005 Location: Lokeren, Belgium	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. __________________ Never send a human to do a machine's job. --Agent Smith

20th September 2010, 07:41 AM	#9
Jonathan Bright diyAudio Member Join Date: Feb 2004 Location: Queensland	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.) __________________ "It was the Spring time of the year when aunt calls to aunt like mastodons across the frozen waste." P.G. Wodehouse. Last edited by Jonathan Bright; 20th September 2010 at 07:45 AM.*


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17th September 2010, 02:16 AM	#2
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	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.

17th September 2010, 04:02 AM	#6
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	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.

20th September 2010, 07:13 AM	#8
Lingwendil diyAudio Member Join Date: Apr 2008	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.

20th September 2010, 07:46 AM	#10
Luke diyAudio Member Join Date: Sep 2001 Location: Wellington NZ	aleph-x sounds ideal for two of these tx's __________________ If you give a man a fish he will eat for a day. But if you teach a man to fish he will buy an ugly hat. And if you talk about fish to a starving man then you are a consultant. Dilbert

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