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June 1968 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 much the same way as
the solution to a word problem seems obvious when you look it up in the back of
a textbook, Sylvania's answer to manufacturing a vacuum tube heater element that
is more robust and less subject to vibration failure is illustrated in this
advertisement which appeared in a 1968 issue of Radio-Electronics
magazine. Eliminating the suspended element and wrapping it securely on a
supporting post facilitated an "instant on" requirement for up-and-coming
transistorized televisions and radios by reducing heat-up time to about a
second. The heater's symmetrical shape also assured even emission of electrons
from the cathode. Its captured winding around the support post also eliminated
the annoying failure mode where a broken-off heater element could fall and
short-circuit grids in the tube. My guess is the reason this method was not used
initially was a materials suitability issue where a support capable of enduring
the extreme temperatures while being non-conductive was not available.
Sylvania High-Voltage Rectifiers
 We've rectified high-voltage rectifiers.
How it used to be.
Our new 3CU3
Take a look at our new "Posted filament" design. There's no delicately suspended
heater-cathode system. There's no need to heat up a metal sleeve and then an oxide
coating.
It takes less than a second, for the 3CU3 to start rectifying full swing.
In case of a break, there's no way for the 3CU3's filament to fall against the
anode, creating a short and knocking out other components in the circuit.
The 3CU3's filament is always perfectly centered. It emits electrons uniformly
in every direction. From a much larger surface than in the old design. There's no
suspension post in the way to create an "electron shadow" that cuts down the plate
current.
The uniform electric field around the rigid support reduces high voltage stresses.
Arcing and its resulting troubles are eliminated.
The 3CU3 is interchangeable with 3A3 and 3A3A high voltage rectifiers. And it's
made exclusively by Sylvania.
The 3CU3 is just one of a new "posted filament" family which includes the new
3BL2 and 3BM2. They're designed for use in new color TV sets. These tubes are especially
good for transistorized TV where their fast warm-up fits in with the "instant on"
feature of solid state circuitry.
The new construction has higher reliability and longer life and should give you
fewer and less troublesome callbacks.
Sylvania a subsidiary of General Telephone & Electronics
From the outside you can hardly tell it's changed.
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