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From: brian@sdcsvax.UCSD.EDU (Brian Kantor)
Newsgroups: sci.electronics
Subject: Does anyone remember the Phantastron tube and how it worked?
Message-ID: <3574@sdcsvax.UCSD.EDU>
Date: Sun, 2-Aug-87 09:11:23 EDT
Article-I.D.: sdcsvax.3574
Posted: Sun Aug  2 09:11:23 1987
Date-Received: Sun, 2-Aug-87 20:27:14 EDT
Organization: UCSD wombat breeding society
Lines: 29

In the middle 70's, the FM transmitter at the college radio station
where I did some of my time was a wonderful old tube widget.  It was a
very reliable device, except for the time the fan motor unbolted itself
and fell into the final cage, causing much arcing and breakage of
glass.  I think it was made by G.E.

It featured a VERY unusual FM modulator using what was termed a
"Phantastron" tube (or maybe it was the circuit).  Unfortunately, the
section of the manual that explained how it worked was klepto'd by
somebody before I got there, so I never really understood how the thing
worked.

It was explained to me that the phantastron tube was basically set up
so that an electron beam travelled from cathode to anode as in most
tubes, but that there was a large magnet clamped around the tube to
force the beam into a helical path to make it longer.  (Yup, you could
see the magnets or something clamped around the tube!)  Apparently
there were a set of electrodes that stretched or compressed the length
of the helix, thus changing the time it took for the electron beam to
traverse the tube, thus phase modulating the signal.

I believed it at the time.  I think I still do.  Is that really how it
worked?

	Brian Kantor	UC San Diego

"You're listening to Jazz-88, KSDS in San Diego... 250 watts of power,
with an effective radiated power of 185 watts.  Someday we're gonna
get a new antenna, folks...."