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TRAFO NEEDED FOR EL84 pp

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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?
 
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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...
 
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.
 
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
 
The suggestion of reverse connecting an isolation trafo is (IMO) suspect. Regulation effects, at rated load, require the trafo be wound with a slight step up.

Voltage doubling the O/P of a Triad N-77U will provide 200+ mA. of B+, which should be quite adequate for a BV. I think you could do far worse than copy the B+ supply used in "El Cheapo". :D
 

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You are pretty much just across the straight from me... i'm sure to have at least 1 suitable trafo (i suspect you'd have to use a 4 diode bridge instead of 2 as the ones i'm thinking of (german made) will be 230-0. Used, not pretty, i'll test it, but shipping will cost more than the trafo (i'd estimate $25 landed in Walla Walla (ie a token $10 for handling & testing + somewhere in the $15 range for post)

dave
 
You are pretty much just across the straight from me... i'm sure to have at least 1 suitable trafo (i suspect you'd have to use a 4 diode bridge instead of 2 as the ones i'm thinking of (german made) will be 230-0. Used, not pretty, i'll test it, but shipping will cost more than the trafo (i'd estimate $25 landed in Walla Walla (ie a token $10 for handling & testing + somewhere in the $15 range for post)

Thanks for the offer Dave, but I plan to build a couple of these so I will need a few of these over time.

I also contacted Edcor yesterday for a quote on a 230-0-230V, 200mA and if comes to about $60-$70 I'll go for it.

How about an Allied 6K56VG (270-0-270) with a choke input.
If I do this then I would require snubbers as well as a choke with a high DC resistance. My total PSU current is about 110mA. To drop 80V (380V pk) I would need a choke with an approximate 700 ohms dc resistance. Any suggestions for this anybody?

Once again thanks for all the input.
 
Tangent: Sakuma Style Amp help?

On another note, I want to design a Sakuma Style amp. Where can I find background information on the circuit theory. I've never done transformer coupling so the concept of input//output impedance matching (using a coupling trafo) and its effect on dist. and freq. response is a bit vague.
 
Where can I find background information on the circuit theory

FWIW, I attended a lecture last month on the Sakuma amps. As best I could tell, there was no theory whatsoever behind it, just the Feelings of Sakuma. So, if I were determined to have a Sakuma amp, I'd just copy a published circuit and not try to guess What Would Sakuma Do.

If you use your own Feelings, it will not be the Feelings of Sakuma.
 
FWIW, I attended a lecture last month on the Sakuma amps. As best I could tell, there was no theory whatsoever behind it, just the Feelings of Sakuma. So, if I were determined to have a Sakuma amp, I'd just copy a published circuit and not try to guess What Would Sakuma Do.

If you use your own Feelings, it will not be the Feelings of Sakuma.

This is amplifier design as mystical art (as only the Japanese can do it). If you change any component in the slightest detail it is unlikely to sound like the original that you are striving for (and that includes the internal wiring).

Good luck.

Shoog
 
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