Page 36 - The Art and Science of Analog Circuit Design

Barry Harvey

record player for the price (it even played a stack of records in sequence).
It worked poorly, but it was a HOME ENTERTAINMENT SYSTEM. We
pay only a little more for similar but better today. Lab equipment was
really rotten then compared to today. There was no digital anything.
Want to measure a voltage? You get a meter, and if you're lucky it has a
vacuum-tube amplifier to improve its range, versatility, and resistance to
burnout. I couldn't afford one; I had a 20KO/V multimeter. I eventually
did wreck it, using it on a wrong range.
In the vacuum-tube days, things burned out. The tubes might only last
a year, or they might last 20 years. Early 2-watt resistors had wax in
them, and always burned out. The later carbon resistors could still burn
out. When I say burn out, I mean exactly that: they went up in smoke
or even flame. That's where the term came from. Where we have cute
switching power supplies today, then the tubes ran from what we call
"linear" supplies that included power transformers which in quality gear
weighed a dozen pounds or more. The rectifiers might be massive tubes,
or they could be selenium rectifiers that also burned up, and they were
poisonous when they did. The bypass capacitors were a joke. They would
eventually fail and spew out a caustic goop on the rest of the innocent
electronics. Let's face it, this stuff was dangerous.
I almost forgot to mention the heat. A typical vacuum tube ran hot; the
glass would burn you if you touched it. The wood cabinets needed to be
regularly oiled or waxed because the heat inside discolored and cooked
them. A power tube ran really hot, hot enough to make the plate glow
cherry-red in normal operation. You could get an infrared sunburn from
a few inches' proximity to a serious power tube. From a couple of feet
away your face would feel the heat from an operating transmitter.
But it wasn't burnout or heat that was the most dangerous thing to an
electronics enthusiast; it was the voltage. The very wimpiest tube ran
from 45V plate potential, but the usual voltage was more like 200V for a
low-power circuit. I made a beautiful supply for my ham transmitter that
provided 750V for the output amplifier. Naturally, it knocked me across
the room one day when I touched the wrong thing; a kind of coming-of-
age ritual. This event relieved me of all fear of electricity, and it gave me
an inclination to think before acting. Nowadays, I sneer at bare electrodes
connected to semiconductors. I routinely touch nodes to monitor the ef-
fect of body capacitance and damping on circuit behavior. I have often
amazed gullible peasants by curing oscillations or fixing bypasses with
only my touch. Of course, the off-line power supplies command my re-
spect. For them, I submit and use an isolation transformer.
At this point, I think we can explain the lack of females attracted to
electronics at the time. In the 50s and 60s, society protected women but
offered men up to danger. The same is true for the earlier industrial revo-
lution: women were huddled into protective work environments and men
were fodder for the dangerous jobs. I think this attitude was prevalent
with respect to vacuum tube electronics. Women (girls, in particular)

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