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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I have a tube that i never thought twice about, and i looked it up and it is a so called gated beam discriminator. It seems that the inside has 2 or 3 separate structures... very strange. Grid one is called signal or limiter, grid 2 is accelerator, and grid 3 is quadrature. The plate is called the plate, and cathode is "cathode, focus electrode, and internal shields". Have a look for yourself: It is a 6bn6 BTW.
So, i am basically wondering what the 2 or 3 different structures are for, and how this thing is different from a pentode.
Edit: Well, i found this: Which makes this thing seem pretty cool, but it still did not answer, what are these things good for? Apparently it is similar in some ways to an AND gate.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
They are used to demodulate FM. Here is a link that also describes the tube you are talking about and some of its uses. Look at figure 3-17 in the link and that might help explain why there are multiple structures. It looks like it could be used for some cool stuff so I might see if I have one and mess around with it.
I guess you could think of it as the reverse of a VCO (voltage controlled oscillator).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
A quadrature detector produces an output signal proportional to the instantaneous value of the input frequency - one of the ways in which a frequency modulated (usually television) signal can be turned into an audio signal.
It is called a quadrature detector because a 90 deg. phase shift is introduced into the signal in order to detect it.
To use this particular kind of FM demodulation, the signal first has to be limited - that is, amplitude fluctuations have to be removed - so that frequency is the only varying component presented to the detector.
This valve was an attempt to provide these limiting and FM detection functions in one envelope, thus saving space - which was always an issue in valve consumer products - also producing less heat, by having only one heater for what was effectively a two-valve process.
Most of these attempts to get a quart out of a pint pot with valves - such as the heptode frequency changer (US: 'pentagrid converter') were never as effective as having the two or more separate valve circuits they were designed to replace.
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What is a gated beam discriminator?
