by Henry Meyer
This project is a means of eliminating the 6V "A" battery for those of us who would like to operate our old battery radios that use 201A type tubes. The most discouraging part of using this equipment is that dry cells are rapidly consumed and automobile batteries are a real pain with their acid and frequent need for charging.
This supply will provide 4.9 to 6.2 VDC (adjustable) at 1.75 amps and slightly less than 6 VDC up to 2 amps, regulated and well filtered.
The heart of the unit is a National Semiconductor device LM309K, a 5V regulator which when used as shown can provide a variable voltage output up to 8 VDC or so depending on components used.
The device is short-circuit proof and has thermal sensing to provide automatic shutdown if the junction temperature overheats. This all provides a real margin of indestructibility and provides a good reliable "A" supply.
The output current capacity because of this is determined by the efficiency of the heatsink provided and using a Motorola MS10, up to 2 amps can be provided without thermal shutsown.
The rectifier I used was a Semtech #SCAJ6, a 6 amp bridge with 50 amp one cycle surge capability which handles charging of the filter capacitor in series with one ohm quite nicely. Any filter capacitor over 3000mf @ 20VDC working voltage should handle the filtering job, and the 50ohm pot. controls the variable voltage output. The transformer is from Radio Shack #273-1511 providing 12.6V @ 3 amps.
The end result of this project has been quite pleasing in that the old Algonquin RF5 radio that sat around for many years after its previous owner passed away is again filling the house with low fidelity sound. Also two Atwater Kents have come out of retirement and must now work for a living.
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