On Mon, 31 Mar 2008 14:05:45 -0600, msg wrote:

Posted to two newsgroups known to be read by likely respondents

The published literature on pre-solid-state electronic analog
multipliers is scant except for production equipment from analog
computer makers (which by now is difficult to locate). One example of a
useful technique is a four quadrant electron beam multiplier described
he

http://dspace.mit.edu/bitstream/1721...9-04734375.pdf

More exotic tubes with curved deflection geometries followed, however
obtaining such tubes is now difficult.

Has anyone at some point tried using sheet-beam deflection tubes as were
used in synchronous detectors and balanced modulator designs for analog
multiplication? I imagine that using four tubes each driven by
quadrant-limited amplifiers and whose outputs would be biased and summed
with scaling may work within a few percent of input values based on a
quick look at the characteristic curves published for these tubes.
Another option would be to add a magnetic deflection yoke over the tubes
to provide a proportional steering of the beam sheet in conjunction with
the electro- static deflection (one of the deflection circuits could be
placed in the negative feedback loop of an op-amp) to reduce the number
of tubes required to two (+/-x, y; +/-x, -y).

It wouldn't take long to breadboard a test circuit for investigation,
but knowing past efforts is always welcome. Surely someone has evaluated
using these tubes in this fashion, even if just for kicks

Michael

Two thoughts:

1: x(1 + y) - x(1 - y) = 2xy. Two beam tubes and a couple of op-amps,
and you're in business. Even with tube op-amps you may use less space
and have less grief from offsets than the space of your quadrant-
switching amp and whatever grief you get from same.

2: There are any number of hot-rod DSP chips that'll fit into a T6-1/2
envelope, complete with ADC's, DAC's and a power supply to run off of
6.3VAC. Sealing the glass up without messing up the DSP may be a
challenge, but you could always fudge and use acrylic.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html