Double EL84 Push-Pull supply - Page 3

fdegrove · 16th January 2003, 10:42 PM

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,

Elkaid · 16th January 2003, 11:03 PM

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... )

fdegrove · 16th January 2003, 11:07 PM

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,

Elkaid · 16th January 2003, 11:11 PM

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 !

planet10 · 17th January 2003, 02:58 AM

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

EC8010 · 19th January 2003, 11:55 PM

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.

Elkaid · 17th June 2003, 02:51 PM

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 !

analog_sa · 17th June 2003, 03:06 PM

Elkaid

Yes.

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

peter

SHiFTY · 17th June 2003, 10:14 PM

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.

Tom Bavis · 18th June 2003, 12:21 AM

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

16th January 2003, 11:07 PM	#23
fdegrove diyAudio Senior Member Join Date: Aug 2002 Location: Belgium	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, __________________ Frank

19th January 2003, 11:55 PM	#26
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	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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16th January 2003, 11:03 PM	#22
Elkaid diyAudio Member Join Date: Jan 2003 Location: Canada	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... )

16th January 2003, 11:11 PM	#24
Elkaid diyAudio Member Join Date: Jan 2003 Location: Canada	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 !

17th June 2003, 02:51 PM	#27
Elkaid diyAudio Member Join Date: Jan 2003 Location: Canada	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 !

17th June 2003, 03:06 PM	#28
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Elkaid Yes. No. But check max supply voltage from the DS. Around 2x28vDC i think. peter

17th June 2003, 10:14 PM	#29
SHiFTY diyAudio Member Join Date: Jul 2002 Location: New Zealand	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.

18th June 2003, 12:21 AM	#30
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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