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June 1963 Radio-Electronics
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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In the midst of the
transition from vacuum tubes to semiconductors, this 1963 Radio-Electronics
magazine infomercial by Mallory offered guidance on modernizing old selenium
rectifiers with the latest silicon versions. This process, commonplace at the
time, symbolized the shift towards more efficient and compact electronic
components. The article provided a detailed walkthrough for replacing these
rectifiers in a standard TV voltage doubler circuit, recommending specific
models such as the Mallory VB500 or pairs of 1N2095's or A500's. It also
cautioned about potential increases in output voltage (B+) post-replacement,
advising the possible need for a dropping resistor. Furthermore, it highlighted
that unchanged B+ voltage could signal faulty filter capacitors, offering steps
for their inspection and substitution if needed.
Mallory - Tips for Technicians: Replacing Selenium with
Silicon Rectifiers
 Mallory Distributor Products Company
P. O. Box 1558, Indianapolis 6, Indiana
a division of P. R. Mallory & Co. Inc.
Ever wonder about replacing those old selenium rectifiers with modern silicon
rectifiers? Stop wondering. It's being done every day and you can do it too! Take
a typical TV voltage doubler circuit for example.
1. You know the seleniums are bad or you wouldn't have started ... right? Right.
2. Forget about the terrific size difference between the new silicons and those
old seleniums. Silicons are smaller because they're much more efficient.
3. Remove the old seleniums and toss 'em in the trash can. Install the new silicon
rectifiers following polarity very very carefully. The slick way is to use a Mallory
VB500 (you'll have one less solder connection to make and the circuit is right on
the rectifier). Or you could use a pair of 1N2095's or A500's. Either way those
Mallory rectifiers will give you the best service you'll ever get.
4. Output voltage (B+) will usually be higher because silicon rectifiers are
more efficient. So, you'll probably need a dropping resistor in series with the
one already there. Turn the set on and check with a voltmeter. Suppose B+ reads
20 volts higher than the schematic calls for. Divide this increase by load current
(perhaps 500 ma) to get the value of the resistor you'll need. (40 ohms in this
case.) Now multiply the voltage increase by current to get wattage rating (10 watts
in this case).
5. But suppose B+ voltage isn't higher. This is a clue that something's wrong
with the filter capacitors. Check them out with a capacitance bridge or try this
very simple deal. Parallel a good TC62 (10 mfd @ 350 WVDC) across each filter in
turn. If you get a marked B+ increase you need some replacement electrolytics. We'd
suggest a Mallory FP, WP, W, or TC of the proper rating.
6. If you'd like a lot more detail on this replacement arrangement, drop us a
line and we'll send a folder by return mail. Meanwhile see your Franchised Mallory
Distributor for all Precision Mallory Components ... batteries, capacitors, controls,
switches, resistors, semi-conductors and vibrators.
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