tektronics 503 scope{Scope Checkout 101}

From: Christian Fandt <cfandt_at_netsync.net>
Date: Sat Dec 12 13:43:42 1998

At 11:29 12/12/98 -0500, you wrote:
>ok, so its not a classic computer but there was a discussion a while back
>about ocilloscopes and i happened upon a model 503 at a thift store for $80.
>is it worth getting? presumably it works but i have no idea how one would test
>it, much less use it.

Well David, this model will not be too useful in troubleshooting a computer.

Looking in my 1966 Tektronix catalog in the specs for the 503 I find that
the bandwith (basically, the calibratable frequency response) of the input
amplifiers is DC to 450 kHz. Short pulses often found in digital logic may
not be seen and a probable logic timing defect would be missed with this
scope. The response of this scope's P2 CRT phosphor is a bit slow too and
though a pulse could be swept by the electron beam the phosphor may not be
bright enough to see it even in a darkened room. This unit would be great
for audio work however (0-20 kHz)!

Besides, $80 is far too much to pay for this model. If you could get it for
around $25-$35 you'd be in the ballpark I think (only IF it works!). You'd
have to get adaptors for any modern scope probes you would buy nowadays.
The input connectors are known as type PL-259. Unless you found early Tek
probes (type P6006 or P6023) at a hamfest you'd need a male PL-259 to
female BNC adaptor. Actually, at the frequencies this scope would be
useful, you could simply get an old set of VOM probes with uncovered banana
plugs and plug them into the center of the PL-259 connector as use them as
is. The scope weighs 29 1/2 pounds.

For those of us working on older computers (with clock speeds of, say <1
MHz to maybe up to 3 MHz) my feeling is to have a 'scope with a freq.
response of at least 20 MHZ so that most short-risetime pulses and glitches
can be caught. A 100 MHz scope would be ideal to see most everything.
However, one day at work I couldn't solve a logic switching problem in a
prototype I was building. Clock speed was 2.0 MHz. I had to drag in my 250
MHz HP 183A scope from home to find it. Our 100 MHz Tektronix missed it.

With todays 50 MHZ+ clock freqs even that 250 MHz scope can't see some
short pulses on a 486 motherboard I've worked with. This is where a good,
fast logic probe is needed or a fancy, expensive very wide bandwidth scope
(1 GHz BW and higher).

David, if you are interested in that scope yet, ask if you could plug it in
and test it. There is a built-in calibrator with two square-wave signal
levels available, 500 mV and 5 mV, at somewhere between 300 and 500 Hz.
Most HP, Tektronix and other high quality scopes have a built-in
calibrator. Take a half meter length of hookup wire along. Strip both ends
back a few mm before you leave the house. I assume you would be able to
figure out how to setup most of the controls on the scope. If not, ask in
private email please. Stick one end of the wire into the center of one of
the Vertical Input connectors and the other into one of the two CAL. OUT
pin jacks. If setup okay and the scope is interested in working then you
should see a square-wave signal somewhere near the CAL. OUT amplitude level
on the screen.

This advice also applies toward you other somewhat inexperienced folks out
there who happen across a scope and would be allowed to do a simple test
before buying.

I call this a "Classic" oscilloscope being over 30 years old. I don't know
the production years of this model though but it was introduced before '66.
It would be great tool to use on an IBM 704! If it was closer to me I'd
like to add it to my Tektronix collection.

Regards, Chris
-- --
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA cfandt_at_netsync.net
Member of Antique Wireless Association
        URL: http://www.ggw.org/freenet/a/awa/
Received on Sat Dec 12 1998 - 13:43:42 GMT

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