"James Sweet" wrote in
news:Qh3fi.573$t95.469@trndny01:


"m kinsler" wrote in message
ps.com...
I'd like to try building an oscilloscope from an old CRT monitor or
TV set. The purpose would be to display audio waveforms at one of
the science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe
I'll need an analog device to show things like the difference in the
audio waveforms of different musical instruments. The big screen of
a TV set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself
with is that the deflection yoke of a CRT is, or at used to be, part
of the high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any
corners on a waveform sent into a vertical deflection coil would be
converted into spikes.

So I'm lazy. Has anyone actually done this sort of thing and
actually had it work to any degree? Thanks.

M Kinsler


It can be done, but the performance is pathetic compared to that you
can get from a $10 Eico or Heathkit oscilloscope. Old basic scopes are
SO cheap now, why bother trying to convert a TV?



You could pick up a used TEK T922/932/935 or TEK 442(T935 in a rackmount!)
for well under $100 on Ebay. That's 15Mhz-35Mhz,simple circuitry,easy to
repair,no TEK-made ICs.
For that you get calibrated graticule,switchable calibrated gain,reasonable
triggered sweep.

--
Jim Yanik
jyanik
at
kua.net