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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Well, how about it, would it be possible to do so?
The one thing that would potentially worry me is as the electron gun fires, the electrons would hit the phosphor screen and then lose all of their energy, thus producing no amplification. Though, another potential idea is to use an oscilloscope CRT, which has actual grids inside of it to deflect the electrons. That could be used as the cathode for the tube, and then just add on deflection coils for the "grid".
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Interesting idea. Please let us know if you find some small CRT's (like you have been looking for) and characterize them as signal amplifiers. Perhaps at relatively low anode voltages, with no need for deflection or sharp focus. I think I can get you some old CRT-based TV camera viewfinders for under $10 each; a regular ebay seller has them routinely for about $15.
One well-discussed variation is amplifiers based on vacuum fluorescent displays and their analog ancestor, magic eye tubes. VFD's are even today going into newly designed consumer electronics and appliances.
There are some 1960-ish decade counter tubes based on e-beam steering, from the era just before transistor-based flip flops. The idea was that a single creatively-designed tube could replace four dual triodes and some or all of a BCD-to-decimal decoder, driver, and display. It would also be nice if it could count much faster than a dekatron (neon plasma stepper motor).
My favorite is the E1T by Philips. A fan-shaped e-beam is electrostatically deflected on one axis, to hit one of ten phosphor numerals on the tube envelope. Part of the beam hits electrodes between each digit, which are electrically coupled to the deflection circuit. That creates ten strong detent positions, and you can ratchet the beam up or down with count pulses of well-controlled amplitude.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The basic idea is sound. EHT regulator tubes like the PD500 contain a triode electron gun firing into a bucket-shaped anode. This results in extremely high mu.
The problem is with the implementation: in a modern CRT, the "anode" is the entire front section of the tube, including the inside of the phosphor screen. It has huge capacitance to ground, so you wouldn't get any bandwidth.
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Using a CRT tube as an amplifier
