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
signal 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 (indicator service)
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 deflectors, etc.
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 Electric
Division of General Electric Company
Schenectady, New York
Posted November 25, 2016