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00940 10th October 2010 01:55 PM

Sanity check on B+ regulator
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Before blowing stuff into little pieces, I'm going to ask before building... is the following regulator ok (nothing new here, it's a well known tubecad design) ? The only real change is the replacement of the TIP50 by a TIP152 (400V darlington with hfe of 200, see datasheet: ). The 40uF caps are mkp.

It will be placed after a 330-0-330, 85mA transformer and an EZ81, to provide 70mA@300VDC (headphones amplifier).

Thanks in advance for any comment.

woody 10th October 2010 02:30 PM

Won't you have about 430v after that EZ81 ? ( (330 x 1.41) - the rectifie voltage drop)

00940 10th October 2010 03:30 PM

You're right. Under a 85m load, the xformer actually gave 415V. However, I'll add 100ohms resistors in serie with the plates of the EZ81 and that should drop quite a lot of voltage (there were none in the scope I've pulled it from). I'll also add a RC filter to get to 360V, whose value will depend on the actual voltages I'll get.

Frank Berry 10th October 2010 03:35 PM

The voltage will still be high until the load begins to draw current. You might be better off installing a bucking transformer on the primary of your power transformer.

00940 10th October 2010 04:04 PM

A cheaper way is to use a string of 4 100V/5W zener after the RC cell. They'll pull the voltage down at startup and will then sit completly out of the way afterwards.

I still wonder how bad that would be, considering the slow warm up of the rectifiers.

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