Sensibly equivalent¶ to:
Type 6BN6 is a late 1940s 'gated beam' valve in which a carefully formed electron sheet or beam is deflected, by control elements on and off of the anode. This 'chops' the amplified signal, typically at a very high rate.
By using two gated beam valves signals from two different inputs can be selected, chopped, or interchanged at any desired rate.
This facility has certain obvious advantages in up-market oscilloscopes designed to show two or more signal traces simultaneously on the same CRT screen. Less obvious but probably more important are multi-channel radar (etc.) receiving applications in which it is vital to amplify parallel signals in different channels with exactly the same gain, even with variable AGC applied. Although the parallel amplifier channels may not be quite identical, by chopping the signals between them each signal is, on average, amplified by the same amount. This is important in radar guidance systems where the ratio of the amplified signals from two or more parallel channels is used to determine the magnitude and direction of the guidance signal. If this were not done the guidance signal output would carry an erroneous bias in favour of whichever channel had slightly more gain.
Type 6BN6 and its brothers are of American design and the gated beam valve was an American invention. However, channel-chopping for military applications was (and still is) very widely used by certain other technically-advanced nations. It is therefore possible that another nation beat the Americans to it. Channel-chopping is still big business in military (and some professional) circles but better ways to do it were soon found. Gated beam valves are nowadays very scarce.
The envelope appears to contain two or three electrode systems, but close examination reveals that there is only one heater/cathode assembly, seen on the left. The ribbon of electrons that are formed (the beam) is guided across the width of the valve to the cavity (anode) on the right of the picture.
Thanks to Brian Cuff for the following information on the 6BN6. I remember this valve being used in the first Ampex video tape recorders the VR1000A. They were used in the demodulators which demodded the video carrier from tape. It was referred to as a gated beam valve and the FM demodulator circuit contained only 1 tuned circuit. At the time, in the very early 1960s, circuit designs existed for the use of the 6BN6 for the reception of FM Band II Radio broadcasts and the solution worked well, however, this was too expensive a solution for manufacturers to adopt for general consumer products.
The first part of the data-sheet is on entry 6BN6.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 57 mm tall.
References: Datasheet & Brian Cuff.
Absolute Maximum Operating Conditions¶
PDF scanned from an original document held by the museum
Updated June 08, 2013. shape:thin.glass.tube construction:all.glass type:pentode age:1940.1950 base:b7g heater:6.3v pins:7 pin:1.k pin:2.g1 pin:3.h pin:4.h pin:5.g2 pin:6.g3 pin:7.a