April 1947 Radio News
[Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Radio & Television News, published 1919-1959. All copyrights hereby
Achieving what we consider relatively
simple results with electronics indicators used to be cutting edge technology. This
6AL7-GT Electron-Ray Indicator Tube by Ken-Rad (a division of General Electric)
provided a dual-channel electrofluorescent (i.e., cathode ray) display of relative
signal strength or tuning the new-fangled FM radio stations. It was promoted in
this 1947 issue of Radio News magazine. The tube could also be used, of
course, for many other applications where
strength from any measured process: fuel level, voltage, temperature, stock price,
phase angle, sound volume, speed, etc., needed to be measured. Today, we have electrochemical
indicators so cheap that they are built into off-the-shelf batteries at Walmart.
Ken-Rad Radio Tube Advertisement
More Accurate FM-AM Receiver Tuning by Means
of Ken-Rad's Revolutionary New Tube!
The 6AL7-GT Electron-Ray Indicator Tube
General Electric research, plus Ken-Rad development work, are responsible for
the brilliant new 6AL7-GT indicator tube - most modern step in the direction of
fast, accurate receiver tuning, FM and AM.
An electron-ray tube, twin light patterns appear on a fluorescent screen at the
end of the glass bulb. These take the form of green bands which vary in depth according
to changing voltages brought about in the process of tuning.
Extremely close FM, discriminator tuning may be accomplished by matching depths
of the 6AL7-GT's light patterns. How the patterns appear to the eye under various
off-channel, on-channel, off-tune, and on-tune conditions, is diagrammed below.
Three FM circuit applications are shown, A fourth - AM - illustrates how avc voltage
may be used for tuning purposes by checking the depth of the two light patterns
working as a unit.
Easy to see and read ... Previous indicator tubes, developed for AM, have had
reflecting targets, giving poor visibility because cathode and deflecting plates
were placed in front of the screen, making it necessary to mask out the center.
The fluorescent screen of the new Ken-Rad FM-AM 6AL7-GT is transparent, with electron-ray
mechanism located behind, not before the image, thus offering no obstacle to vision.
Ken-Rad is consistently ahead with new tube developments - meaning that Ken-Rad
dealers, and servicemen installing Ken-Rad tubes, march in the van of radio progress.
Pioneering work by Ken-Rad, as typified by this great new 6AL7-GT indicator tube,
enables you to serve all your clients better, whether their radio sets be AM or
FM, old-style or new, portables or console models ... Install Ken-Rad tubes for
greater owner satisfaction, and resulting bigger profits!
Ken-Rad's outstanding new indicator tube will be on view at the Chicago Parts
Show, May 13 through 16. See how it tunes circuits to hairline accuracy with ease
and precision! Your visit to the Ken-Rad display will be one f the highlights of
your Chicago trip. A cordial welcome awaits you!
Typical Operating Conditions
Heater voltage 6.3 v
Heater current 0.150 amp
Target voltage 315 v
Voltage, deflection electrodes 1, 2 and 3 0 v
Cathode resistor (approx) 3,300 ohms
Deflector sensitivity (approx) 1.0 mm/v
Fluorescence cut-off, grid volts (approx) -6.0 v
Cutaway view of a Ken-Rad 6AL7-GT, showing screen target, grid, electron-ray
The 6AL7-GT's principle of operation is unique and effective. In the cutaway
drawing at the right, note that the three deflection electrodes are close to the
cathode, with this whole assembly in turn separated from the target by the grid.
The latter operates either at cathode potential, or at a few volts negative with
respect to the cathode. Because electrons move slowly in the area between cathode
and grid, the 6AL7-GT's deflectors easily control the position of the electron beams
on the target. Increasing the negative voltage on the grid slows down the electrons
still more, augmenting their response to the deflectors' pull and thus heightening
the tube's sensitivity.
More detailed technical information and performance data on the 6AL7-GT will
be furnished promptly on request. If you manufacture electronic equipment, Ken-Rad
tube engineers gladly will work with you to apply the new Indicator Tube to radio
receivers or test equipment you may have on your drawing-boards. Communicate direct
with Ken-Rad at the address below.
Behind Ken-Rad radio tubes stands Electronics' first and greatest name - General
Division of General Electric Company
Schenectady, New York
Posted August 4, 2022
(updated from original post