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Old 9th February 2006, 06:31 PM   #1
poynton is offline poynton  United Kingdom
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Default HT regulator using 78xx

Hi.

Can a 78xx ( or other cheap regulator) be used to regulate a voltage of around 200v for a valve preamp??

or is a high voltage transistor with zeners adequate?

I'm not looking for anything sophisticated - just simple and working.

Any help appreciated.

Andy
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Old 9th February 2006, 06:33 PM   #2
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The 317 is suitable and cheap. Go to the National Semiconductor site and search for the applications note on this from Michael Maida.
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Old 9th February 2006, 06:39 PM   #3
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yes, as the thing is purely floating.
Though use a diode (250 PIV) across the unit as a safeguard against the countercurrent if the feeding supply might get lower than the destination...
I used this already in 1984!
It will give around 5-10 mV ripple/noise.
You can put a small capacitor on the voltage intersection (100 nF) to reduce noise. But then also this must be brigden with a diode to the destination to ensure the "ground termminal" never is higher than the Vout or the unit will break down when the output goes down too fast.

Whether the simple zener/transitor is ok depends on the feed: often a zener will hardly be 'quiet'.
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Old 9th February 2006, 06:50 PM   #4
poynton is offline poynton  United Kingdom
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Hi.

OK guys - enough info for now!!

Thanks for the quick replies - much appreciated.

Andy
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