On Fri, 13 Aug 2004 03:49:15 +0000 (UTC),
(Ken Smith) wrote:

In article ,
Fred Bloggs wrote:


John Larkin wrote:


Looks like the jfet will be saturated with the values shown, not good
for RF work. Looks like he got the sign of Vgs backwards. The next
example on the same page illustrates that Vg must be near zero, not
+5. Really silly, putting these two circuits side-by-side.

John


Shhhh...don't tell the resident idiot, but it's going to be damn tough
biasing that IDSS=5mA JFET to a quiescent ID=10ma....

Theres no problem getting 10mA to flow in a FET with Idss of 5mA. Just
apply a positive bias to the gate. I've had as much as 2 or 3 A flow
through a JFET this way.



Jfets make pretty good pA-leakage diodes, although the series
resistance tends to be higher than for a "real" diode. Never tried one
as a power rectifier.

Jfets don't enhance much, but gaasfets - especially phemts - enhance a
lot, typically 1.6 * Idss just before the gate begins conducting in
earnest. That can be useful.

John

On Fri, 13 Aug 2004 12:54:14 +0000, Mike Andrews wrote:

In (rec.radio.amateur.homebrew), Fred Bloggs wrote:

Paul Burridge wrote:
On Fri, 13 Aug 2004 03:49:15 +0000 (UTC),
(Ken Smith) wrote:


Theres no problem getting 10mA to flow in a FET with Idss of 5mA. Just
apply a positive bias to the gate. I've had as much as 2 or 3 A flow
through a JFET this way.


How many mS did the Fet last? I suppose you could always stand there
with a can of arctic spray directed on it, but I doubt the customer
would be impressed. ;-)

Actually there have been systems produced that did run quite hot and
were arranged with a liquid nitrogen drip onto the electronics to keep
things cool.

One model of Seymour Cray's computers ran with the logic immersed in
a bath of chilled Fluorinert or some such, with a fairly hefty pump
to keep the coolant recirculating through the chiller.

Many years before, IBM was going to use a CFC (FC86, IIRC) in much the
same way. The logic modules were about 4" cubes with a multi-layer
(50-60, can't remember) ceramic substrate with 100 logic chips on one
side, a water-filled cold-plate on the other, and filled with the CFC.
Heat was removed from back-side of the chips by boiling the CFC. I worked
on a logic tester in '75 that immersed the un-encapsulated substrate into
a bath of CFCs so it could be probed.

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips. The result came to be known as the "black
plague". Because of the "black plague" the "LEM" (Liquid Encapsulated
Module) was replaced by a similar looking (though shorter) "TCM" (Thermal
Conduction Module) which used pistons on the backside of the chips
(increased to 121 chips) to transfer heat (10W per chip, 1200W total) to
the cold-plate and filled with helium. The TCMs were used throught the
'80s and early '90s for the high-end ECL systems.

--
Keith

I read in sci.electronics.design that Keith wrote (in
) about 'Error in textbook?',
on Sat, 14 Aug 2004:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips.

Sulfur hexafluoride might have been better, but it's probably more
costly than CFCs were.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

In (rec.radio.amateur.homebrew), Keith wrote:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips. The result came to be known as the "black
plague". Because of the "black plague" the "LEM" (Liquid Encapsulated
Module) was replaced by a similar looking (though shorter) "TCM" (Thermal
Conduction Module) which used pistons on the backside of the chips
(increased to 121 chips) to transfer heat (10W per chip, 1200W total) to
the cold-plate and filled with helium. The TCMs were used throught the
'80s and early '90s for the high-end ECL systems.

Yep. I've got a TCM somewhere at home; I need to take a pic of it
for my web page. IIRC, it has 1024 pins, and the largest ZIF socket
I've ever seen. The cold plate on the TCM is about 4.5" square, very
smooth, and designed to go on a larger water-cooled manifold with some
dozens more TCMs, all getting water from a chiller.

They're called "wet-frame" machines by a lot of us who dealt with
them, and especially by those of us who had a leak develop somewhere
in the cooling system.

Nowadays one TCM's circuitry fits on a single chip, at a meager
fraction of the TCM's dissipation, and is enormously faster, so that
(for 9672 hardware, anyway) IBM ships the machine with a bunch of CPUs
and licenses you the code to turn on as many as you're paying for. If
you want more than ship in the base machine, they'll install another
dozen pretty cheap.

And the homebrew and design connections:

They're sure not homebrew, and they're more than one designer can do.

--
Mike Andrews

Tired old sysadmin

On Sat, 14 Aug 2004 18:24:14 +0100, John Woodgate wrote:

I read in sci.electronics.design that Keith wrote (in
) about 'Error in textbook?',
on Sat, 14 Aug 2004:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips.

Sulfur hexafluoride might have been better, but it's probably more
costly than CFCs were.

Cost? Dunno. I do know that we were paying $50/qt (IIRC) for the stuff
in '75. I wouldn't think a sulfur/fluoride brew could be made any
"cleaner" than CFCs. THe problem was the contaminants.

--
Keith

On Sat, 14 Aug 2004 20:53:24 +0000, Mike Andrews wrote:

In (rec.radio.amateur.homebrew), Keith wrote:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips. The result came to be known as the "black
plague". Because of the "black plague" the "LEM" (Liquid Encapsulated
Module) was replaced by a similar looking (though shorter) "TCM" (Thermal
Conduction Module) which used pistons on the backside of the chips
(increased to 121 chips) to transfer heat (10W per chip, 1200W total) to
the cold-plate and filled with helium. The TCMs were used throught the
'80s and early '90s for the high-end ECL systems.

Yep. I've got a TCM somewhere at home; I need to take a pic of it
for my web page. IIRC, it has 1024 pins, and the largest ZIF socket
I've ever seen.

I think you'll count a lot more than 1024 pins. The ones I worked on int
the '70s had 1800. There were 1280 signal pins (I rember that name
because of the logic tester - the LT1280).

The cold plate on the TCM is about 4.5" square, very
smooth, and designed to go on a larger water-cooled manifold with some
dozens more TCMs, all getting water from a chiller.

Twelve TCMs for each processor, and nine for each channel (for the 3080s).
A system could have upwards of a hundred of these beasts in it. Later
sytems had fewer since the logic density increased. ...which is what
ultmately killed them. The infrastructure was simply too expensive for
the quantity needed.

They're called "wet-frame" machines by a lot of us who dealt with them,
and especially by those of us who had a leak develop somewhere in the
cooling system.

****ers, eh? I was once tasked to design a "leak detector" for exactly
thi sproblem. I brought in the guts out of a toilet (complete with copper
float) and told them to put these under the floor with a switch. Come on!
Detect a leak in a pipe a few hundred feet long passing many gallons per
minute?

Nowadays one TCM's circuitry fits on a single chip, at a meager fraction
of the TCM's dissipation, and is enormously faster, so that (for 9672
hardware, anyway)

Note that the first CMOS machines were slower than those they replaced (in
direct violation of IBM's "prime Directive"). THough they were
significantly cheaper and with more processors (loophole alert).

IBM ships the machine with a bunch of CPUs and
licenses you the code to turn on as many as you're paying for. If you
want more than ship in the base machine, they'll install another dozen
pretty cheap.

"Install"? ;-) They'll enable as many as you want, for as long as you
are paying. We called this "Rent-A-MIP". THere is even a crypto unit in
there if you want to use it.

And the homebrew and design connections:

They're sure not homebrew, and they're more than one designer can do.

Yeah, there were a few designers doing this stuff. ;-)

--
Keith

Keith wrote:

On Sat, 14 Aug 2004 18:24:14 +0100, John Woodgate wrote:

I read in sci.electronics.design that Keith wrote (in
) about 'Error in textbook?',
on Sat, 14 Aug 2004:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips.

Sulfur hexafluoride might have been better, but it's probably more
costly than CFCs were.

Cost? Dunno. I do know that we were paying $50/qt (IIRC) for the stuff
in '75. I wouldn't think a sulfur/fluoride brew could be made any
"cleaner" than CFCs. THe problem was the contaminants.

Yeah, and whether you're working with a liquid or gas, it's the contaminants
that make it dirty. I'd think a gas could be cleaner already just by not
dissolving a bunch of solids, although the solids in suspension can be
even smaller than in a liquid. But those aren't going to condense out.
They might collect as dust, but if that's your problem, then you have
a lot worse problem than contaminated fluid!

I guess my point is, it wasn't the CFC's fault that it was contaminated.

And, FYI, AIUI, SF6 is really quite inert. You make it sound like fire
and brimstone, for heaven's sakes! ;-)

But it has raised a good question - which makes a better heat transfer
agent? Helium or SF6? (gases only, of course ;-) )

Cheers!
Rich

In article ,
says...
Keith wrote:

On Sat, 14 Aug 2004 18:24:14 +0100, John Woodgate wrote:

I read in sci.electronics.design that Keith wrote (in
) about 'Error in textbook?',
on Sat, 14 Aug 2004:

Unfortunately, boiling the CFC also distilled it, leaving any
contamination on the chips.

Sulfur hexafluoride might have been better, but it's probably more
costly than CFCs were.

Cost? Dunno. I do know that we were paying $50/qt (IIRC) for the stuff
in '75. I wouldn't think a sulfur/fluoride brew could be made any
"cleaner" than CFCs. THe problem was the contaminants.

Yeah, and whether you're working with a liquid or gas, it's the contaminants
that make it dirty. I'd think a gas could be cleaner already just by not
dissolving a bunch of solids, although the solids in suspension can be
even smaller than in a liquid. But those aren't going to condense out.
They might collect as dust, but if that's your problem, then you have
a lot worse problem than contaminated fluid!

The issue was that during the phase change the contaminants were left
behind. They were soluble in the liquid, but have a far higher BP than
85Cish so they're distilled *onto* the chips.

I guess my point is, it wasn't the CFC's fault that it was contaminated.

I didn't blame the CFC. I don't "blame" inanimate objects. ;-) No
matter how clean the CFCs any trace contaminate deposited on the parts
that were boiling, exactly where you don't want the contamination.

And, FYI, AIUI, SF6 is really quite inert. You make it sound like fire
and brimstone, for heaven's sakes! ;-)

I tried to look up SF6's properties, but got nowhere. I don't think it
could have replaced CFCs. The particular CFC was chosen for its
precise boiling point.

But it has raised a good question - which makes a better heat transfer
agent? Helium or SF6? (gases only, of course ;-) )

Note that the He was aided by pistons contacting the back of the chip
(C-4 mounted). It was a much different and more complicated package
than the LEM.

--
Keith