tubes age 26
fullsize octal based 0x3 type with these problems. I think that all of those that
I'm using were built during WWII. or before It was only by accident that I found
that the scope was a good tool for finding a bad one. I was looking for a totally
unrelated problem and happened to scope the 150V line on a receiver that had
no apparent noise. Nasty looking for "DC". Using a VTVM, the voltage was a
nice ~150 volts. I got to wondering and started swapping 0A2's and 6626's from
my spares and noticed that about half of them were erratic as hell. Since then,
the 0A2 is at the bottom of my list as far as a "trustworthy" tube in the R390A's.
>It takes 15 or 25 volts above the voltage rating to fire and so long as
>the current through the tube stays above 5 or 10 ma the tube is in a
>stable region. But if the current gets lower,
OK, gotcha. The current getting lower thru the regulator tube would be caused
by an increased somewhere else in the receiver on the +150 line.
>or the tube characteristics change because of a different gas pressure, the
tube can
>stop conducting which lets the voltage rise up to the trigger voltage
>then the voltage drops while the tube takes current...
Interesting. I never thought about it from that stand point. It might be possible
then that under those circumstances that a decrease in the level of the isotope
in the tube could cause problems. I need to dig out all of the tube manuals and
see if there's anything interesting on VR tubes that I've either not paid attention
to or forgotten.
>A zener diode at the same voltage is not as fine a regulator. My solid
>state circuit that I've not yet bread boarded would do much better. Need
>to try that some time.
I never was a big fan of zener diodes. My first run in with them was on my old
Triumph and BSA motorcycles as a kid. That soured me for life on them. They
were used to shunt excess charging voltage to ground. Hey, no moving parts! ;-
( Stupid Lucas electrical system...
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Date: Sat, 22 Jan 2000 21:31:31 -0600
Subject: Re: [R-390] 0A2 testing
(14 pages)
(10 pages)
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