On Jan 17, 6:18*pm, "Eisboch" wrote:
"Del Cecchi" wrote in message

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"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

I'd like to find a cool vacuum tube project to make steampunk.