bias resistors. On the testing unit, two
pairs of precisely matched millimeters
exhibited each tube's plate and
screen element. Another single meter
(a VTVM) was employed to read
control grid emission/gas with a
toggle switch to select either tube.
There was also a DC voltmeter to
read the B+ power supply which was
variable in order to match different
tube types. There was a standby
switch in B+ only. The unit housed a
5" speaker to indicate noise. Also, the
unit had two preheat sockets
(elements only) which hastened the
interchange of tubes.
Over the years, I added nine-pin
tube socket adapters. We could
match 807, 5881, 6L6G, 6V6GT,
6CA7, 6550, 6BQ5, etc., tubes.
During the matching process, the
tubes were run hard with high plate
current (thanks to the various
cathode resistors and adjustable B+)
to achieve class "A" test levels.
Many of my Soundmaster
amplifiers are still around today and
have become high priced collector’s
items. With over 30,000 built and
sold under warranty, I expected that
a certain percentage would be
returned to the factory for repair.
That work — which I thought might
keep me busy in later years — never
materialized. I have, however, been
able to see one of my amps in use
after 60 years and, remarkably, the
output tubes still read as balanced
with satisfactory frequency responses
and noise levels.
In addition to highest quality
parts and excellent hand-wiring, the
careful balancing of the output tubes
with my tube matcher was definitely
an important reason for our success.
It served me well over the years. We
tested so many tubes with it that I
had to replace sockets on occasion.
According to my calculations, we
matched over 100,000 tubes.
Hy Bloom, CEO (Retired)
( The following feedback is in regards
to the Christmas can light dimmer
article in the December 2013 issue.)
Although I like the article's
concept, there is a safety issue here.
Even though the neutral wire is
connected to earth ground at the
circuit breaker box, devices should
never rely on the neutral wire for a
safety ground as was done in this
project. Since the dimmer enclosure
is aluminum, a shock hazard exists if
the 120 volt outlet hot and neutral
wires are reversed (which is not
uncommon) because the aluminum
enclosure would then be at a 120
volt potential. Nowhere in the article
does the writer verify that the outlet
is wired properly. Using three-
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50 January 2014
READER FEEDBACK Continued from page 7