4Aac and 42Vac is 168VA.
That would be cost effective in powering one channel that could be anywhere from 84W to 168W.
If you want that one transformer to power two channels for stereo then the total maximum output of both channels can be between 84W and 168W.
I would consider a 42Vac 2Aac transformer poor value in terms of performance /£ of the complete amplifier, if the specified maximum total output power were 180W. i.e. 90W + 90W onto 4r0 + 4r0. from an 84VA transformer.
For a little extra money and extra size and extra weight, the performance can and will be increased by using a higher VA rated transformer. going to 120VA should show a significant sound quality improvement. Going to 250VA should show a further improvement, but possibly not as big a jump as the first stage increase. Going to 400VA and you have entered a completely different performance bracket. The whole amplifier must be redesigned to use and survive the power that is available and will be demanded by the speakers if domestic party duty is ever envisaged with real current hungry, reactive speakers.
What I can confirm is that the Thermal and Electrical stresses that the output stage have to experience will be very different for the four different current ratings of the same Vac transformers.
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I will be back in the weekend and tell about my final decision ! 😀 I have 6 x 500 VA 2x 30 VAc toroids and they are Danish . Not the **** to buy at RS Components. They are making a lot of mechanical noise because the are done very bad.
I don't approve of the single insulated mains feed to the transformer (pink pair).
Is there more that you can see that worries you?
I'm wondering if the Scott transformer you nominated was not 42-0-42V and 325VA, Erland, or you would not be concerned about high voltage or even if it was suitable for split rails. Is that so perhaps?
Andrew, I have some nice silicone Dynel sheathed primary leads here. Not pink but quite the rugged looking 130 degree business. 'Pity they won't be needed in my cool running amps.
Andrew, I have some nice silicone Dynel sheathed primary leads here. Not pink but quite the rugged looking 130 degree business. 'Pity they won't be needed in my cool running amps.
This Scott 007-9810562 have a lot of outputs. They are all coupled in series.
325 W could maybee be right !
Changed Transformer and Voltage
So I removed the Scotts and in came an 500 VA 2 x 30 VAC . 2 X 42 VDC .
I set the bias to 260 ma. It is only hand warm 45 celsius aprox .
Will listen later on the week.
So I removed the Scotts and in came an 500 VA 2 x 30 VAC . 2 X 42 VDC .
I set the bias to 260 ma. It is only hand warm 45 celsius aprox .
Will listen later on the week.
The bottom is the top. (case is custom 3-side heatsink)
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