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Hi,
here is some hands-on experience with buying a 7912AD at ebay:

Half a year ago i got a 7912AD at ebay for US $ 50. It was shipped from US to
Germany by USPS surface for about US $ 90. When it arrived it was in good shape,
though the processor hang on powerup self tests. Anyway it is a really interesting
device: Its circuits are about 3 times more complex than a normal 7000 scope. It
has everything inside that was high-tec in the 80s, from ECL to AM2900 bit slice
processor. Its modular switched 350 W power supply must have been a shock for Tek
competitors (appears to be prototype of modern PC power supplies).

So i decided to buy service manuals and fix it. This was another US $ 300 + about
20 hours of work. In addition i bought a programmable amplifier 7A16P and a
programmable time base 7B90P for about US $ 120 + shipping. Later i noticed, that
7A16P is the proper amplifier for a 7612 digitizer and i needed a 7A29P instead.
That one i got for another US $ 170 + shipping. You also need a black and white TV
monitor to do adjustments.

So you see: Owning such a device is not for the fainthearted and the impression
you get, when somebody buys something cheap at ebay may be completely misleading.
For me the total was about $ 1000.

You also see: For an educated engineer a 7912AD is still maintainable. Now i have
a scope that dumps its electron beam into a semiconductor target of about 1" by
1". The target serves as realtime storage and is read out by a second beam in
three different modes:
- TV scanning
- xy intensity scanning
- xy intensity scanning with analog to digital conversion, storage and data
transfer via HPIB.

The images i get are perfect, including a grid written by the beam! Bandwith is
about 500 MHz. The sampling rate equivalent to the risetime of about 0.6 ns would
be 1.6 Gs/s.
Now the drawback: it does only about 512 samples total! This is why everybody
wants to have one of these modern digital storage scopes with megabytes of memory
and why the concept of 7912AD is history.

Anyway, for applications where the small number of samples doesn't matter, a
7912AD still competes with modern $ n0 000 scopes. This is in the area of
scientific measurements, where you know when you expect an interesting event to
happen, so you can catch it inside your 512 samples record. In the world of
digital communications a 7912AD gets lost and you better buy a used TDS scope for
the same price.

Owning such a superb device as a private person may be an interesting experience,
especially for a true Tek freak. I bought another one in the meantime.. mmm,
because each one has only one input channel!

Best regards
Dieter Teuchert



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I guess that conversation took place before I joined. Could someone tell
me - briefly - what the digitizer is good for? And what else would one need
to go with it to make it useful?

P.S. I recently bought a box called an Auto-Cal Steering Unit. I actually
bought it for the box ($5 + S&H)
but now that I've looked inside, I find it intriguing. I'm especially
curious as to what connects to the two
centronics-like connectors on the back. Any background would be
appreciated.
-----Original Message-----
From: Craig Sawyers [mailto:c.sawyers@...]
Sent: Tuesday, January 15, 2002 2:57 AM
To: TekScopes@...
Subject: [TekScopes] Digitizer on eBay

Hi

A heads-up for anyone wanting a 7912 digitizer that we were discussing on
the list a few days ago. There is one listed on eBay, item 1690813203
with
a $19.99 start bid. It weighs 70lb, so it is not one for me - shipping
costs to the UK would be astronomical.

Craig

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Hi Dean,

I think the two color DVST came later (post 1976-77). When I first saw the
4081, it was green on green, as were the Battlestar Galactica shots (sorry,
don't have either the pilot movie or the series on tape to see). I can't
confirm which later Tek terminal models had the two color feature. I believe
they retrofited the color write-through to the 4081 workstation, but don't
remember if it become a 4082 or some such other product. A catalog from that
period should provide the answer. Either way, the stored image was always
green.

The write-through feature (mono or two color) was not present on the
older/more common DVST (direct view storage) displays as used on the 4051
desktop computer, or the 4010, 4012 et al (getty fuzzy on numbers again...)
dumb graphics terminals. With those you had to manually erase the screen at
some point--sort of like an etch-a-sketch. Or you couldn't see anything new
that was written as the screen filled up. Erase could happen under software
control also. The write-through enhancement answered the need to provide an
animation capability. Write-through with color was a further development; I
believe to provide better contrast between stored and non-stored images. I
don't know too much about that technology. I have the Pete Keller CRT
history book--I will see if mention is made of that technology in there. I
would assume it's discussed, though I haven't read the book entirely yet.

I was always fascinated by watching the DVST write. Modern high info content
displays are so boring by comparison--except perhaps color plasma. Of
course, I prefer vacuum tubes and steam engines also.

Speaking of display technologies for Wilsonville applications....

By around 1980, everything from Wilsonville seemed to be going to 19"
diagonals (CAD graphics). I remember the saying was in Display Research
(part of Tek Labs) that "Wilsonville wasn't interested in any new display
technology that couldn't be expanded to 19". I worked on the color shutter,
which wasn't so valuable on the bigger screens but was particularly suited to
small area, high resolution applications. It was a successful technology as
applied to the color TDS series digital scopes, some of which are still in
production. In the early 80's, a 1240 style logic analyzer was to use the
limited color version (red/green/yellow), but when it wasn't quite ready, the
product group had commissioned a clever two color CRT instead. The shutter
was also adapted to 3D displays, which spun out of Tek "kinda", but I don't
know much about that.

Matrix EL was another Tek developed display technology which would eventually
stretch to 19", though from Planar Systems years after we split off from Tek.
As far as I know, we are the only company to produce EL panels that large
(for DEC terminals, who sold them principally to the financial market, but at
a markup so large that volume never built up). That size was unusual
however, as our volume has, and remains, with panels smaller than 10.4"
diagonal.

Electon beam addressed EL (an "EL CRT") was also promising for it's high
resolution, but never made it to commercial application as far as I know. My
recollection was it never made it past 5" diagonal prior to my departure from
Tek in '83. I also helped complete a summer student's fascinating
"LED-o-scope" project, which involved a spinning mirror with a vertical array
of yellow LEDs. The LEDs scrolled out the image one vertical line at a time
as the mirror rotated. I believe there was also an additional short column of
red and green LEDs to show limited color capability. Definitely wasn't
scaleable to 19", but was a fun 6" (?) demo.

The CRT light valve (electron beam addressed LCD) was also an interesting Tek
Labs technology being pursued while I was there (at that time, monochrome).
Don't know where this went, but think of any LCD projector today and you'll
get the idea (though the latter use matrix LCDs, not electron beam addressed).

In the end, Wilsonville moved away from DVST to raster scan (as memory prices
tumbled), and so they stayed until the end.

Wups. Rambled once again.

Don

PS: I've enjoy your postings Dean. All very interesting!




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Just to add from Pete Keller's book, "The Cathode-Ray Tube Technology,
History and Applications", he refers to the "Anderson bi-stable, direct-view,
storage tube developed by Robert Anderson of Tektronix...and first introduced
commercially in the Model 564 storage oscilloscope in 1963." Prior to that
he mentions "the Hughes Products type 6498 Memotron (1956) was the first CRT
desgined specifically for storage of oscilloscope waveforms and was used in
their models 103 and 104 storage oscilloscopes."

Trying to remember what Stan said earlier, sounds like he might have the
earliest Tek storage scope eval sample (the Tek scope with the Hughes tube)?




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I believe the manufacturer of the 4 pin plug Dean refers to is LEMO in
Switzerland. Beautifully machined metal parts (reminds me of a fine

and gold contact pins. Pulling on the outer shell activated the latching
prongs. When Planar split off from Tek, I designed them into our flat

burn-in racks as the panel bulk drive connector. Expensive connector, but
very reliable. Another super example of why I was so wowed by the Tek
engineering stock. Couldn't find anything like that at any hobby

store!