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Old 16th January 2003, 11:42 PM   #21
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Default reversed xformers

Hi,

Quote:
It will work, but there are safety issues to be considered before putting it into service.
As said,you'll get the voltage but the current can endanger the xformers' insulation.

IOW if the current draw is neglectable you can get away with it.

Not good practice for any design IMO.

Cheers,
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Old 17th January 2003, 12:03 AM   #22
Elkaid is offline Elkaid  Canada
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Thank you

I guess that if I want to prevent the transformer from melting, I should choose a higher rated transformer

Example :
4 X EL84 @ 60mA each = around 240mA

I suppose that a 160-200 transformer should do the job right ?

(You've probably guessed that I'd do anything to lower the overall cost of the amp... )
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Old 17th January 2003, 12:07 AM   #23
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Default IN THEORY

Hi,

In reality you're still facing mother natures' law of physics and you're not likely to save $ either.

If and when it goes South it'll take your hard earned cash with it +
the likelyhood of other damage to the circuit as well.

No such thing as a free lunch,
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Old 17th January 2003, 12:11 AM   #24
Elkaid is offline Elkaid  Canada
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Only one last solution : Ask a company specialized in custom transformers. Costs much more....

Finally the idea of using more standard transformer and adding a choke and everything seems the most elegant approach.

Thanks !
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Old 17th January 2003, 03:58 AM   #25
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Quote:
Originally posted by Elkaid
(You've probably guessed that I'd do anything to lower the overall cost of the amp... )
You could always just start with a thrashed Dynaco SCA35 or appropriate Scott with good iron...

dave
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Old 20th January 2003, 12:55 AM   #26
EC8010 is offline EC8010  United Kingdom
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Default Custom transformers

No-one seems to have mentioned it, but transformer manufacturing is a "cottage industry" and you can have "one-offs" made for a very reasonable price if necessary. Old transformers are generally cheaper, but perhaps don't do exactly what you want. If you do go for a new transformer, insist on an electrostatic screen between mains and HT, and also between HT and heaters. It will cost extra, but it's worthwile.
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Old 17th June 2003, 03:51 PM   #27
Elkaid is offline Elkaid  Canada
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Hi guys !

I was just wondering if a 220V center-tapped transformer is the same thing as a 2 X 110V secondaries connected together ?

Sometimes, I'm really missing some electronics basic knowledge


And oh, by the way, is there any problems when connecting 4ohms speakers to a Gainclone ? (Without forgetting that I shouldn't push it too far)

Thanks !
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Old 17th June 2003, 04:06 PM   #28
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Elkaid

Yes.

No. But check max supply voltage from the DS. Around 2x28vDC i think.

peter
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Old 17th June 2003, 11:14 PM   #29
SHiFTY is offline SHiFTY  New Zealand
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If you know a few old radio repair shops, they can sometimes have transformers, chokes, tubes and so on just lying around. Or you can scavenge them from old tube gear (PA amps etc.) You can buy an old PA amp with a couple of 6L6 on ebay quite cheaply, which would probebly be enough for 4x EL84.

Takes a bit more imagination to use, but beats paying for new ones...

Pretty much all my iron is "recycled". Transformers seem to last a long, long time if treated well and not overheated.
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Old 18th June 2003, 01:21 AM   #30
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I know some would differ with me, but _I_ would use a 120:120V isolation transformer and a voltage doubler to get about 300V. (It was good enough for Fisher, McIntosh, HK Citation II...) Or a 120:220V step-up transformer and a full-wave bridge. You'd need 100VA at least for the plate supply, and if you use a toroid (Hammond), you can wind your own secondary for the 6V. In that case, use 130 VA at least. See the amp on my web page for an example: http://www.audiophool.cjb.net/Audio.html
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