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Old 20th February 2012, 07:44 PM   #601
RevMen is offline RevMen  United States
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As always, thanks for the fast response, Salas.

It seems like this one should work. Do you think so?
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Old 20th February 2012, 08:09 PM   #602
Salas is offline Salas  Greece
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No, see rightmost column, it gets to 2C/W under forced convection, i.e fan blower.
You need 2C/W on natural convection.
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Old 20th February 2012, 09:41 PM   #603
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Understood, but the 2 C/W is for a downward facing orientation (flat side on the top). If I set it on its end, convection will be more efficient. Still, though, I don't know how much more efficient, so it's probably best not to guess.

I reckon I don't understand how to determine how much heatsink is needed. I was thinking in terms of the 11W dissipation at dT=60 for natural convection, which I suppose would mean ~6.4 W at dT=35 (60C-25C). And I suppose that allows us to dissipate 21 mA at 300V, or have I got that wrong?

How much spare current would we expect in this circuit? Would it be higher or lower than 20 mA?
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Old 20th February 2012, 09:53 PM   #604
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When you got over 40C in a valve circuit box such a sink can rise up to 75C. 300Vx0.02A= 6W and a 2C/W will get you to 55C in a hotter day which is much more agreeable. When having 55C on a sink its not difficult to have 100C plus on the silicon junction to have a picture. Don't skimp on sink area, this is constant current giving it no cooling off cycle %. 20mA spare is the recommended compromise. If you give it 30mA the reg's spec gets better and so it goes. Measure 60C max on your sink for max spare after half an hour in real box is a safe rule of thumb.
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Old 2nd April 2012, 07:31 PM   #605
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How should turntable chassis ground tie into the circuit?
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Old 2nd April 2012, 08:09 PM   #606
Salas is offline Salas  Greece
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To a chassis post while the chassis will be at ground potential with one wire from PSU 0V.
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Old 4th April 2012, 03:09 PM   #607
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OK, thanks. That makes sense. Does it make sense to tie PSU 0V to the chassis at the location of the chassis post? Or does that matter?
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Old 4th April 2012, 03:16 PM   #608
Salas is offline Salas  Greece
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It usually doesn't matter.
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Old 8th April 2012, 11:18 AM   #609
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Has anyone tried the RIAA caps that Felipe organised for us? I'll admit that I'm very reluctant to open mine up - its sounding fantastic! Would be interested to hear people's opinions vs the Russian caps...


Fran
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Old 8th April 2012, 11:34 AM   #610
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I still not tried, did you tried?
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