N9WOS wrote:
On the other hand, it does seem like a LOT of work to go to
considering that you can get a really nice used analog scope for under
$100. I have an HP1715A 200MHz 2-channel scope with nice main+delayed
sweep that I need to put on ebay (or equivalent), and I seriously
doubt I'll get $100 for it.

I have the old scope laying around so why not? And almost everything I am
using in it is salvaged parts. Including capacitors, transistors,
transformers, and the video chips in question. I will probably have under 10
dollars in it after I am done. (That includes the $5 I paid for the scope a
few years ago.)

If you do go to all the trouble to revamp your Eico (maybe the same
scope model I started with almost 50 years ago??!!), I do hope you'll
put a good triggered sweep in it, and not just a "horizontal
oscillator." It's not too difficult to make a very respectable linear
sweep with op amps and fast comparators these days. For triggering,
for example, have a look at the Analog Devices ADCMP02 and its
siblings: fast, built-in hysteresis... I'm using one in the input of
a counter, and it goes to 100MHz easily for low level inputs, and to
well over 200MHz if I jack up the input a bit.

For the sweep, I was planning on using a transistor as a constant current
source to charge the capacitor for a nice linear sweep. And use JK or D flip
flops for trigger and state control. The flip flops would be triggered and
reset by comparators.

The clock input to the flip flop will be feed from a comparator and used as
the trigger input. When the capacitor reaches a certain value (end of sweep)
a comparator would reset the flip flop. When the flip flop rests, it will
discharge the cap. After a dwell time (cap discharge period), the data input
to the flip flop will be brought high. The next clock input (trigger) will
set the flip flop and the cap will start charging which commences the sweep.

I should be able to do the sweep and triggering circuit with a dual D flip
flop, a quad comparator, and a transistor with some other components. with a
comparator and D flip flop to spare.



Thanks for posting this interesting topic! I thought no one else cared
about CRTs. I've been messing with scopes and CRTs a long time. It's
always fun. I always see the 3" tubes built into people's projects,
running on 1-3KV. They are never very bright. I like the larger 5" ones
of recent manufacture (recent being a relative term). Half the fun is
doing it yourself. Even the HV supply is a fun project when you get into
serious scope tubes. In general, it will take at least 6KV to get a real
bright one going. - but the tube has to be able to take it! In case
anyone needs a good CRT, there are many here, for cheap, and quite a few
HP or TEK types:
http://www.magnetosphere.net/

PJ