TRAFO NEEDED FOR EL84 pp

audio_moksha · 8th January 2008, 05:34 PM

Hi all,

I am looking for a really cheap power transformer for a 10W EL84 PP amp in class AB. It is loosely based on Morgan Jones' Bevois Valley Amplifier. I need a 230-0-230 @ 150mA power transformer. Where can I get them ready made and cheap? Hammond does not make lower voltage power transformers with high current ratings. I laso checked Edcor with no success. I plan to make a couple of these so any suggestions?

EC8010 · 8th January 2008, 05:41 PM

How about an isolating transformer with a hybrid bridge rectifier? (You have 240V mains in Oz?)

audio_moksha · 8th January 2008, 05:45 PM

I'm in the US so 120V. Also I've never used an isolating tranny before. Morgan Jones also referred to these in his designs. Could you shed more light please? Many thanks..

EC8010 · 8th January 2008, 05:51 PM

My apologies, I saw Walla Walla and assumed it was in Oz. An isolating transformer is used by builders (bricks and mortar type) and service engineers to make mains operated kit safer. The important bit is that the market is rather large, so they tend to be cheap. Problem is that they are 1:1, so a US isolating transformer will produce only 110V...

pedroskova · 8th January 2008, 06:06 PM

Triad makes the N66A, 250VA, with split primaries. If you were to run it in "reverse", i.e., the primaries(wired in 240V) used as secondaries, and vice versa, it might work. They retail @~ $60 at Mouser, but I bought one for $15.00 off of epay.

I'm not using it in the way mentioned above. Hope this helps.

sorenj07 · 8th January 2008, 07:33 PM

Or you can run a 1:1 transformer in a voltage doubler.

EC8010 · 8th January 2008, 07:56 PM

Quote:

Originally posted by sorenj07
Or you can run a 1:1 transformer in a voltage doubler.

Good point.

Ty_Bower · 8th January 2008, 08:19 PM

How about this Antek toroid?
http://cgi.ebay.com/ws/eBayISAPI.dll...m=370011609801

Wavebourn · 8th January 2008, 08:37 PM

Look for a "signal transformer" on e-pay.

Shoog · 8th January 2008, 08:40 PM

Where the wide bandwidth of a toroidal transformer is an advantage in an output transformer, it is a disadvantage in a power transformer.
This is because it is more able to carry high frequency crud from the power line into your amp. There is an amazing amount of high frequency crud on power lines. If you use SMPS and CFL then even more so.

Shoog

8th January 2008, 05:34 PM	#1
audio_moksha diyAudio Member Join Date: Oct 2006 Location: Los Angeles	TRAFO NEEDED FOR EL84 pp Hi all, I am looking for a really cheap power transformer for a 10W EL84 PP amp in class AB. It is loosely based on Morgan Jones' Bevois Valley Amplifier. I need a 230-0-230 @ 150mA power transformer. Where can I get them ready made and cheap? Hammond does not make lower voltage power transformers with high current ratings. I laso checked Edcor with no success. I plan to make a couple of these so any suggestions?

8th January 2008, 05:41 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	How about an isolating transformer with a hybrid bridge rectifier? (You have 240V mains in Oz?) __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

8th January 2008, 05:51 PM	#4
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	My apologies, I saw Walla Walla and assumed it was in Oz. An isolating transformer is used by builders (bricks and mortar type) and service engineers to make mains operated kit safer. The important bit is that the market is rather large, so they tend to be cheap. Problem is that they are 1:1, so a US isolating transformer will produce only 110V... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

8th January 2008, 08:37 PM	#9
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Look for a "signal transformer" on e-pay. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

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8th January 2008, 05:45 PM	#3
audio_moksha diyAudio Member Join Date: Oct 2006 Location: Los Angeles	I'm in the US so 120V. Also I've never used an isolating tranny before. Morgan Jones also referred to these in his designs. Could you shed more light please? Many thanks..

8th January 2008, 06:06 PM	#5
pedroskova RIP Join Date: Dec 2002 Location: C'ville VA, USA	Triad makes the N66A, 250VA, with split primaries. If you were to run it in "reverse", i.e., the primaries(wired in 240V) used as secondaries, and vice versa, it might work. They retail @~ $60 at Mouser, but I bought one for $15.00 off of epay. I'm not using it in the way mentioned above. Hope this helps.

8th January 2008, 07:33 PM	#6
sorenj07 diyAudio Member Join Date: May 2006	Or you can run a 1:1 transformer in a voltage doubler.

8th January 2008, 08:19 PM	#8
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	How about this Antek toroid? http://cgi.ebay.com/ws/eBayISAPI.dll...m=370011609801

8th January 2008, 08:40 PM	#10
Shoog diyAudio Member Join Date: Aug 2002 Location: Eire	Where the wide bandwidth of a toroidal transformer is an advantage in an output transformer, it is a disadvantage in a power transformer. This is because it is more able to carry high frequency crud from the power line into your amp. There is an amazing amount of high frequency crud on power lines. If you use SMPS and CFL then even more so. Shoog

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