REGULATED B SUPPLY Henry Meyer Some time ago, I wrote a short article on an A supply for up to 6, 201A's and threatened to someday generate a B supply. At the May get-together at Foothill College, I saw Glen Streeter's excellent power supplies, which I think were a bargain at the price, however, I sat down and wondered if a person couldn't generate a satisfactory "B" supply at a price what we can all justify and this is what I tried to do. All components are garden variety and can be obtained at Radio Shack, Poly Paks or may be had in the junk box. It provides 22, 45, & 67 volts at 60 ma. Going to a higher voltage would require a more specialized transformer and was avoided for this reason, plus the fact that 67 volts provides plenty of loudspeaker volume and is easier on scarce tubes.

After building the supply, I found that the output filtering was necessary due to little or no decoupling in the old sets, and noise generated by the zener diodes. The circuit is designed around a voltage doubler circuit which charges the capacitors to 2.8 times the RMS value of the transformers secondary. The main regulator is accomplished on the 67 volt line and the 45 and 22V lines are zenered down from this point and filtered. The only requirements are that the regulating transistor should have a 100 volt collector to emitter rating, and be able to dissipate 10 watts or so, being very conservative as most power transistors can handle considerably more power, thus making the voltage rating more important. The Zener diodes that reduce the voltage to 45 & 22V should be rated at 4 to 5 watts, being conservative. The unit has been in operation for a couple of weeks now and with the output filtering and bypassing 3, 47uf capacitors, operation has been satisfactory and uneventful. Copyright 1978 California Historical Radio Society, all rights reserved. No part of this publication may be reproduced in any form, or by any means, without prior written permission from CHRS, except that you may make "fair use" of quotations of text fully attributed by you to the source (CHRS Journal) and author. CHRS PO Box 31659 San Francisco, CA 94131