21 Apr
2005
21 Apr
'05
5:46 p.m.
My 'EPROM Eraser' uses a multi-element tube.
It's actually an old quack
medical device from the 1950's. It's a big 'cold quartz' UV lamp, and
has a high voltage power supply in the base that uses one of the 'newer'
versions of a multifunction tube, the 117L7GT, which is a tube with a
117 volt filament and (I believe) several different tube stages.
Yes, the '117' at the start of that number means a 117V hater, which can
go straight across US mains [1]. IIRC, the 117L7 is a combined power
pentode (designed for audio output) and a half-wave rectifier. One of the
valves I mentioend for cheap record players.
[1] US valve numbers start with a string of digits which gives the heater
volvtage (but watch out for '7' and '14' which are actually 6.3V and
12.6V o na Loctal baxe). UK Maxda valve codes look similar (they're of
the form digit - letters - digits), and again the first set of digits
normally gives the heater voltage _apart from 10, 20, 30_ which are
series string heater valves for 100mA, 200mA and 300mA chains.
Now why do I rememebr this stuff?
Probably the _last_ versions of multifunction vacuum tubes were the
'Compactron' tubes, specifically designed multi-element tubes used in
the 60's and 70's in sets sets designed to use with fewer tubes, i.e.
portable tube-type televisions. Compactrons were in an envelope similar
in shape to the common 7 and 9 pin mini tubes, but bigger with (if I
recall correctly) 12 pins.
IIRC, The Tektronix 556 'scope is full of Compactrons. Fortunately my 555
isn't...
-tony