Once I had a little problem with my septic tank (sewerage system) and needed to get
some air into it. I went to the local pet shop and bought a fish tank pump that did
the job just fine.
However, they also had a special; a free gold fish with every purchase.
Terrific.
Then of course, I needed a tank, filter, gravel, underwater toys and Doo Dads. I
already had the pump (when not otherwise in use, it had two outlets anyway).
So after getting all the accessories all was well, with fishy happily swimming round
in his new home, until one day he went to the great fish tank in the sky.
A friend finally got the tank, etc.
Now if I go to buy a reel of solder and the day's special is a Tek. Digitizer, well
perhaps I'll just pass it up.
Still, if ever I need to conduct any underground tests?
I know how you feel Dieter. At least you won't have to buy a manual for the next one.
Cheers, Don Black.
Dieter Teuchert wrote:
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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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