"Eisboch" wrote in message
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"Del Cecchi" wrote in message
...

"Canuck57" wrote in message
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On 16/01/2010 6:17 PM, wrote:
On Sat, 16 Jan 2010 14:05:54 -0800 (PST), Frogwatch
wrote:

Here at work, we are repairing the vacuum control circuitry for
an
electron microscope made in 1979. It has 6 SN7400 chips. If I
remember, these are quad 2 input NAND gates. 2 of them have
gone bad
because the heat sinking of the board is not very good, you can
see
heat discoloration on the board.
Back in 1974, I was 18 and was experimenting with making
computer
circuitry trying to make a computer cpu with a calculator chip
and a
buffer made from a bunch of 7400 gates as memory flip flops. I
never
got rid of all those old chips and still have several tubes of
them
unused.
Now, 36 years later, I find a use for them.

Never throw anything away ;-)

There are still plenty of places that still stock these things. I
never took the TTL plunge because I had IBM parts to play with
but I
have made a lot of CMOS (4xxx) stuff. Couple that with a big SSR
and
you can run humongous stuff straight from CMOS. (like my 11kw spa
heater)

Same deal, just that you are likely a few years yonger. Every TTL
has a CMOS counterpart in time and CMOS was a better/newer
evolution of the TTL. Used both myself but mostly TTL.

Was fun to tinker with those chips on bread boards. A joy many
today will never know.

I always wondered if the US government got a hold of an ancient
space ship and reverse engineered the electronics we have today.
As we accelerated down this path about as fast as socially
possible without regards to the hardware.

I remember saying to people at the time that it is unlikely I will
retire before we see a 4ghz computer with 4 CPUs and 4gb of ram
and 4gb of hard drive as a commodity system.

Only 4ghz CPU stands between me and retirement. Bu the rest is
history.

You are a couple of years overdue. Put in those papers.

Depending on your definition of commodity of course.

http://www-03.ibm.com/press/us/en/pr...ease/21580.wss


I remember TTL logic being the rage in the late 70's. The problem
for electrically noisy
industrial applications was that a "high" was about 3.8 volts and a
"low" was around 2.4 volts.
A TTL logic based controller would work fine in the quiet lab, but
when it was used in a
real application and subjected to harsh RFI and EMI environments,
there was no way of
telling what it would do. It didn't take much of a electrical spike
or some RFI to completely screw up
the logic.

CMOS at 12 volts worked much better.

Vacuum tubes worked perfectly. (and still do).

Eisboch
TTL up level was 2 volts, down level was 0.8
at the input. The output was 2.4 and .4 for 400 mV of noise immunity.

S and LS was a little different. I've still got a TI manual with the
gold covers on my bookshelf.

Vacuum tubes worked OK for some things if you didn't need long life,
reliability, and had plenty of power to waste. If you want to make a
solid state amp sound like vacuum tubes, put some resistance in series
with the speakers, to simulate the higher output impedence.

del