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Old 28th February 2012, 08:27 PM   #61
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Well, heck, yeah!!!! Since we to "direct couple" the stages of our audio systems, why not "direct couple" our power rail requirements directly to our (local) power mains. Just think--eliminate the cost and weight of the toroid....

Hhhhmmmm--wondering about the safety considerations.....
For all of you "just dialing in". My comment above was in jest. I'd never design or build a circuit without a mains transformer--just for isolation from the mains, if nothing else.

Please don't try what I mentioned.....or if you do, please don't come looking for me afterwards.

I used to own a "universal" AC/DC transformerless shortwave radio (National Radio NC-60). It's amazing how I ever survived playing with that thing. Don't try this at home.....!!
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Old 28th February 2012, 09:03 PM   #62
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How many output pairs from 2SK1530/2SJ201 (12A - 150W) do I need to run the amp with +/-75V rails and it's still safe at 2 ohm loads?

Thanks
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Old 29th February 2012, 01:09 AM   #63
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A lot.
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Old 29th February 2012, 01:48 AM   #64
a.wayne is offline a.wayne  United States
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How many output pairs from 2SK1530/2SJ201 (12A - 150W) do I need to run the amp with +/-75V rails and it's still safe at 2 ohm loads?

Thanks
Is this for domestic use? 75volt rails are not needed if running @ 2ohms , 40 volt rails will work with standard v3 , you will need 16 outputs/ ch to run 75v rails and of course modified driver stage ...
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Old 29th February 2012, 01:54 AM   #65
BigE is offline BigE  Canada
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V=I*R. 75 = 37.5 * 2.

Would'nt you need 6 pairs, assuming you want to run 1/2 the rated current through each?
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Old 29th February 2012, 08:51 AM   #66
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Suppose worst dissipation at 40V , 40 x 40 / 2 = 800W.
Max die temperature is 150C, 125 above 25C ambient.
On an infinitely large heatsink, 1 output device with a mica insulator could handle a little over 90W.

So 6 pairs would sufficient, with a heatsink that does 0,05 C/W.
Easy peasy with fan blown tunnel.
It's the cooling that's vital, not the output devices, with MOSFETs.
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Old 29th February 2012, 10:33 AM   #67
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Which classA power intended?
I have lost the track.
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Old 1st March 2012, 01:37 AM   #68
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Daniel wanted Class AB, 100mA bias per device.

At 2 Ohm continuous duty, power losses (Verlustleistung in German is better word) will be tremendous.
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Old 1st March 2012, 01:57 AM   #69
6L6 is online now 6L6  United States
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For what it's worth, Nelson has talked me out of using 65v rails on an F5Tv3. The voltage is too high and It would be running too near the edge.

Of course, Fearless Amplifier Builders can try it, but know that it's going to be a bit of a beast.
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Old 1st March 2012, 08:37 AM   #70
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With a small engine in the front, smarter to go bridged/balanced for higher output, imo.

(amps are like trucks, high power requires more gears)
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