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7S/7T Sampling System

 

Does anybody have a 7T11A or plain and a 7S11A or plain sampling system that
is in good condition. Need a good one to do some 067-0587-XX's. Not being
re-sold...for my use...saw that being asked this morning.

Thanks,
Dan Tulloss
Senior Metrologist
National Test Equipment, Inc.
760-639-1700
760-639-1799 Fax
www.nationaltestequipment.com
Dennis Tillman
 

Hi Dan,

Which 067-0587 are you talking about? the -02 is a 1GHz unit but the -01 is
slower (500 Mhz I think). I think the -00 is slower still. I ask becaue that
will determine how fast the sampling heads need to be.

A 7T11A is much rarer and more expensive than a 7T11. Unless you need the
7T11A version (which is what a 7854 scope needs) there is nothing wrong with
the 7T11. You will need a sampling head to go in the 7S11 such as an
S1/S2/S3/S3A/S4. Note the S1, S3, and S3A only go to 1GHz.

Have you considered a 7S14 instead of a 7T11/7S11/Sx. The 7S14 is often
overlooked because it is one of the original 7000 plugins. The 7S14 is a 1
GHz Dual Trace Sampling plugin with the sampling heads and a delayed
timebase all built in to a very easy to use self contained unit. It is quite
nice. They can be had cheaply. It occupies two slots. So on a 4 slot
mainframe you can still use a real time amplifier and timebase at the same
time.

Dennis

-----Original Message-----
From: Dan Tulloss [mailto:dtulloss@...]
Sent: Monday, March 01, 2004 3:22 PM
To: 'TekScopes@...'
Subject: [TekScopes] 7S/7T Sampling System


Does anybody have a 7T11A or plain and a 7S11A or plain sampling system that
is in good condition. Need a good one to do some 067-0587-XX's. Not being
re-sold...for my use...saw that being asked this morning.

Thanks,
Dan Tulloss
Senior Metrologist
National Test Equipment, Inc.
760-639-1700
760-639-1799 Fax
www.nationaltestequipment.com
Gottfried Ira
 

Is there a writeup or a brief overview describing the
differences between the A and non-A versions?

Thanks,
Gottfried Ira


Dennis Tillman wrote:

Hi Dan,
Which 067-0587 are you talking about? the -02 is a 1GHz unit but the -01 is
slower (500 Mhz I think). I think the -00 is slower still. I ask becaue that
will determine how fast the sampling heads need to be.
A 7T11A is much rarer and more expensive than a 7T11. Unless you need the
7T11A version (which is what a 7854 scope needs) there is nothing wrong with
the 7T11. You will need a sampling head to go in the 7S11 such as an
S1/S2/S3/S3A/S4. Note the S1, S3, and S3A only go to 1GHz.
Craig Sawyers
 

Have you considered a 7S14 instead of a 7T11/7S11/Sx. The 7S14 is often
overlooked because it is one of the original 7000 plugins. The 7S14 is a 1
GHz Dual Trace Sampling plugin with the sampling heads and a delayed
timebase all built in to a very easy to use self contained unit.
I don't think that necessarily helps - the full cal procedure for the test
fixures calls for a 7S12; a pulse generator (S52) is used to supply a clean
and fast pulse and the two sampling heads look at the + and - differential
signals coming out. The ampifier compensation is then tweaked to minimise
aberrations. I guess that a 7S14 could be used with a seperate 100ps
pulser, but that would only do for the -00 suffix fixture. The -01
procedure calls for S2's with 4.6GHz bandwidth. I don't have the procedure
for the -02.

Craig
 

Without knowing details of calibration, let me point to a power
supply/fixture 283 (I think) that supplies power to S52 and feeds trigger
signal to front panel. Something like that could be used to get signal out
of S52 when 7S12 is not available. Alternatively, a 284 can be used as a
pretty good signal source.

While on the sampling gear subject, could someone tell me more about S4. I
have been told that construction of S4 is quite terrible, so sampling pulses
blow by on the bridge is significant and low level signals can be drown in
that noise. I gentleman who told me about that, said that he almost scrapped
amplifier that he was building, but power meter showed no noise, so he went
out and found S6, which confirmed that amplifier was all right.

The S4 has marginally higher bandwidth, but because of that rumor I stayed
away from it and opted for S6.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Craig Sawyers" <c.sawyers@...>
To: "TekScopes Yahoo Group" <TekScopes@...>
Sent: Tuesday, March 02, 2004 8:24 AM
Subject: RE: [TekScopes] 7S/7T Sampling System


Have you considered a 7S14 instead of a 7T11/7S11/Sx. The 7S14 is often
overlooked because it is one of the original 7000 plugins. The 7S14 is a
1
GHz Dual Trace Sampling plugin with the sampling heads and a delayed
timebase all built in to a very easy to use self contained unit.
I don't think that necessarily helps - the full cal procedure for the test
fixures calls for a 7S12; a pulse generator (S52) is used to supply a
clean
and fast pulse and the two sampling heads look at the + and - differential
signals coming out. The ampifier compensation is then tweaked to minimise
aberrations. I guess that a 7S14 could be used with a seperate 100ps
pulser, but that would only do for the -00 suffix fixture. The -01
procedure calls for S2's with 4.6GHz bandwidth. I don't have the
procedure
for the -02.

Craig
Craig Sawyers
 

While on the sampling gear subject, could someone tell me more about S4. I
have been told that construction of S4 is quite terrible, so
sampling pulses
blow by on the bridge is significant and low level signals can be drown in
that noise. I gentleman who told me about that, said that he
almost scrapped
amplifier that he was building, but power meter showed no noise,
so he went
out and found S6, which confirmed that amplifier was all right.

The S4 has marginally higher bandwidth, but because of that rumor I stayed
away from it and opted for S6.
Well, there are some reports on the Picosecond Pulse labs website that they
produced during the 80's and early 90's with tests on sampling systems.
They found that there was a problem with the S4:

"The old Tek S4 sampler had the worst settling time performance. It showed
a gradual rise in 4ns to a max overshoot of 5.5% followed by an exponential
decay back to the 100% level requiring an additional 25ns."

"We found that the 200ps wide strobe caused a unique problem for the S4.
When a tunnel diode pulser was mounted directly on the input connector of
the S4, the leakage of the 200ps strobe was enough to cause false triggering
of the TD. The falsely triggered TD pulse would then enter the S4's diode
bridge during the 200ps on time. The resulting CRT waveform was quite
unstable, with sometimes a negative risetime display. The simple cure for
this is to introduce a delay line between the pulse generator and the
sampler. The delay must be greater than the strobe pulse duration. Thus
for the S4 a 500ps, 7mm (diameter) air line was used."

"Close inspection revealed that the S4 response had a very fast rise time,
with flat response for 200ps. At 200ps it has an abrupt +7% step. Then the
waveform continues to rise up to the 105.5% level in about 4ns. It then
slowly recovered back to the 100% level in 25ns. The Tek spec is <=10% and
some units used by the author in the past have been as bad as 10%."

By contrast, the S6 gets a much better write up - a mere single paragraph
that says it it much better than the S4. The other head that gets a really
good write up by PPL is the SD24. The benchmark for their tests was the
Hypres superconducting Josephson Junction sampler, which boasted a pulse
response of 5ps (70GHz).

Craig
Dennis Tillman
 

The article, by Mark Kahrs, on sampling systems that was just mentioned
yesterday on the TekScopes site covers the entire history of sampling
systems and sampling test equipment. It discusses in some detail the
differences between the S1/S2/S3/S4/S5/S6 and the pros and cons of each
design. Its worth downloading and reading up a copy if you want to know
which plugin is best for which application.

Unfortunately I no longer have the link. The link to Mark Kahrs web site is
but I can't find the paper there at the
moment. It is on his site somewhere.
Dennis

-----Original Message-----
From: Craig Sawyers [mailto:c.sawyers@...]
Sent: Tuesday, March 02, 2004 2:29 PM
To: TekScopes Yahoo Group
Subject: RE: [TekScopes] 7S/7T Sampling System


While on the sampling gear subject, could someone tell me more about S4. I
have been told that construction of S4 is quite terrible, so
sampling pulses
blow by on the bridge is significant and low level signals can be drown in
that noise. I gentleman who told me about that, said that he
almost scrapped
amplifier that he was building, but power meter showed no noise,
so he went
out and found S6, which confirmed that amplifier was all right.

The S4 has marginally higher bandwidth, but because of that rumor I stayed
away from it and opted for S6.
Well, there are some reports on the Picosecond Pulse labs website that they
produced during the 80's and early 90's with tests on sampling systems.
They found that there was a problem with the S4:

"The old Tek S4 sampler had the worst settling time performance. It showed
a gradual rise in 4ns to a max overshoot of 5.5% followed by an exponential
decay back to the 100% level requiring an additional 25ns."

"We found that the 200ps wide strobe caused a unique problem for the S4.
When a tunnel diode pulser was mounted directly on the input connector of
the S4, the leakage of the 200ps strobe was enough to cause false triggering
of the TD. The falsely triggered TD pulse would then enter the S4's diode
bridge during the 200ps on time. The resulting CRT waveform was quite
unstable, with sometimes a negative risetime display. The simple cure for
this is to introduce a delay line between the pulse generator and the
sampler. The delay must be greater than the strobe pulse duration. Thus
for the S4 a 500ps, 7mm (diameter) air line was used."

"Close inspection revealed that the S4 response had a very fast rise time,
with flat response for 200ps. At 200ps it has an abrupt +7% step. Then the
waveform continues to rise up to the 105.5% level in about 4ns. It then
slowly recovered back to the 100% level in 25ns. The Tek spec is <=10% and
some units used by the author in the past have been as bad as 10%."

By contrast, the S6 gets a much better write up - a mere single paragraph
that says it it much better than the S4. The other head that gets a really
good write up by PPL is the SD24. The benchmark for their tests was the
Hypres superconducting Josephson Junction sampler, which boasted a pulse
response of 5ps (70GHz).

Craig





Yahoo! Groups Links
 

It appears he has two nearly identical sites.

The site including the paper is:

The link to the paper is:

- greg

-----Original Message-----
From: Dennis Tillman [mailto:Dennis@...]
Sent: Tuesday, March 02, 2004 3:42 PM
To: TekScopes Yahoo Group
Subject: RE: [TekScopes] 7S/7T Sampling System


The article, by Mark Kahrs, on sampling systems that was just mentioned
yesterday on the TekScopes site covers the entire history of sampling
systems and sampling test equipment. It discusses in some detail the
differences between the S1/S2/S3/S4/S5/S6 and the pros and cons of each
design. Its worth downloading and reading up a copy if you want to know
which plugin is best for which application.

Unfortunately I no longer have the link. The link to Mark Kahrs web site is
but I can't find the paper there at the
moment. It is on his site somewhere.
Dennis
Stan & Patricia Griffiths
 

After reading Dennis's message, it occured to to me to look up the 7S14 in a
Tek catalog. This is just a 1 GHz, two channel, 50 ohm sampler. Tek made a
lot of earlier versions of this technology that are a LOT cheaper on the
market than the 7K stuff. So if the 7S14 is really up to this job, you
might want to consider the following:

661/4S1/5T1A (there are other plugins you could use in this system: 4S2,
4S2A, 4S3, 5T1, 5T3)

561A/3S76/3T77 (and lots of other plugins and mainframes you could use
here, too: 561, 564, 561B, 564B, 3S3, 3S1, 3S2 [sampling heads required},
3T77A, 3T2)

There is also a 5000 series sampler: 5S14

The important thing to keep in mind is that you generally need some
mainframe, a sampling vertical, and a sampling timebase to work as a system.
Virtually all of the 661 system plugins will work together and virtually all
of the 561A mainframes and plugins will work together. It may be tricky
getting a system up and running, however. Fixing those old sampling systems
was sort of "black magic" even when all the parts (tunnel diodes and GaAs
diodes) were available new from Tek. Now, I suspect, you would need several
"donor" instruments to find enough good parts and then there is still the
"black magic" . . . I have read postings about using some fast Schotky
diodes in place of some of Tek's GaAs diodes but I have no personal
experience with this . . .

Regarding the "black magic", I can say this. In the late 60's, I was one of
the founders of an independent service company that specialized in only
Tektronix stuff in Southern California (it was called Mobilscope, Inc. and
we were based in Van Nuys, CA, and traveled Southern California in several
"calibration trailers" right to the customer's doorstep.) Anyway, fixing
and calibrating Tektronix sampling was our strongest suit and we used to do
them for most of the other cal labs in LA who had to farm them out when they
got stuck. We did a ton of them for large companies all over So. Cal. (No,
I am NOT interested in doing any for anyone else at this point in my life!
I have a bunch of old Tek sampling instruments and I hope to get several
systems running eventually, for my collection.) I would consult with people
who own some of this old sampling stuff and are trying to make it run,
however. Email me about it and I will see if I have any advice for you.

Stan
w7ni@...

----- Original Message -----
From: "Dennis Tillman" <Dennis@...>
To: "TekScopes Yahoo Group" <TekScopes@...>
Sent: Monday, March 01, 2004 4:16 PM
Subject: RE: [TekScopes] 7S/7T Sampling System


Hi Dan,

Which 067-0587 are you talking about? the -02 is a 1GHz unit but the -01
is
slower (500 Mhz I think). I think the -00 is slower still. I ask becaue
that
will determine how fast the sampling heads need to be.

A 7T11A is much rarer and more expensive than a 7T11. Unless you need the
7T11A version (which is what a 7854 scope needs) there is nothing wrong
with
the 7T11. You will need a sampling head to go in the 7S11 such as an
S1/S2/S3/S3A/S4. Note the S1, S3, and S3A only go to 1GHz.

Have you considered a 7S14 instead of a 7T11/7S11/Sx. The 7S14 is often
overlooked because it is one of the original 7000 plugins. The 7S14 is a 1
GHz Dual Trace Sampling plugin with the sampling heads and a delayed
timebase all built in to a very easy to use self contained unit. It is
quite
nice. They can be had cheaply. It occupies two slots. So on a 4 slot
mainframe you can still use a real time amplifier and timebase at the same
time.

Dennis

-----Original Message-----
From: Dan Tulloss [mailto:dtulloss@...]
Sent: Monday, March 01, 2004 3:22 PM
To: 'TekScopes@...'
Subject: [TekScopes] 7S/7T Sampling System


Does anybody have a 7T11A or plain and a 7S11A or plain sampling system
that
is in good condition. Need a good one to do some 067-0587-XX's. Not
being
re-sold...for my use...saw that being asked this morning.

Thanks,
Dan Tulloss
Senior Metrologist
National Test Equipment, Inc.
760-639-1700
760-639-1799 Fax
www.nationaltestequipment.com





Yahoo! Groups Links
Dennis Tillman
 

It is apparent to me now that a 7S14 would not meet Dan's (Dan Tulloss,
Senior Metrologist, National Test Equipment, Inc.) needs.

I have one of each of the Tek sampling plugins: 7S11/7S12/7S14/7T11/7T11A,
and all but one the sampling heads:
S1/S2/S3/S3A/S4/S5/S6/S50/S51/S52/S53/S54) and I've used them all. From
personal experience the 7S14 is my favorite because it is so simple. But
because it is less capable than the others it is often overlooked.

The 7S14 was a sampling system designed for people familiar with dual trace,
dual timebase real time scopes. I recommended it for someone that has never
used sampling before because it is easy to use and it is self contained. It
works well up to 1GHz. They are available on eBay from time to time at a
reasonable price (under $100). There is one auctioned right now (item
#3801463517, current price $11.00) at
<
By the way, the only sampling head I am missing in my collection is the S42
(55pS Optical Sampling Head). Does anyone know where I can buy one?

Thanks, Dennis

-----Original Message-----
From: Stan & Patricia Griffiths [mailto:w7ni@...]
Sent: Wednesday, March 03, 2004 12:42 PM
To: Dennis Tillman
Cc: TekScopes
Subject: Re: [TekScopes] 7S/7T Sampling System


After reading Dennis's message, it occured to to me to look up the 7S14 in a
Tek catalog. This is just a 1 GHz, two channel, 50 ohm sampler. Tek made a
lot of earlier versions of this technology that are a LOT cheaper on the
market than the 7K stuff. So if the 7S14 is really up to this job, you
might want to consider the following:

661/4S1/5T1A (there are other plugins you could use in this system: 4S2,
4S2A, 4S3, 5T1, 5T3)

561A/3S76/3T77 (and lots of other plugins and mainframes you could use
here, too: 561, 564, 561B, 564B, 3S3, 3S1, 3S2 [sampling heads required},
3T77A, 3T2)

There is also a 5000 series sampler: 5S14

The important thing to keep in mind is that you generally need some
mainframe, a sampling vertical, and a sampling timebase to work as a system.
Virtually all of the 661 system plugins will work together and virtually all
of the 561A mainframes and plugins will work together. It may be tricky
getting a system up and running, however. Fixing those old sampling systems
was sort of "black magic" even when all the parts (tunnel diodes and GaAs
diodes) were available new from Tek. Now, I suspect, you would need several
"donor" instruments to find enough good parts and then there is still the
"black magic" . . . I have read postings about using some fast Schotky
diodes in place of some of Tek's GaAs diodes but I have no personal
experience with this . . .

Regarding the "black magic", I can say this. In the late 60's, I was one of
the founders of an independent service company that specialized in only
Tektronix stuff in Southern California (it was called Mobilscope, Inc. and
we were based in Van Nuys, CA, and traveled Southern California in several
"calibration trailers" right to the customer's doorstep.) Anyway, fixing
and calibrating Tektronix sampling was our strongest suit and we used to do
them for most of the other cal labs in LA who had to farm them out when they
got stuck. We did a ton of them for large companies all over So. Cal. (No,
I am NOT interested in doing any for anyone else at this point in my life!
I have a bunch of old Tek sampling instruments and I hope to get several
systems running eventually, for my collection.) I would consult with people
who own some of this old sampling stuff and are trying to make it run,
however. Email me about it and I will see if I have any advice for you.

Stan
w7ni@...

----- Original Message -----
From: "Dennis Tillman" <Dennis@...>
To: "TekScopes Yahoo Group" <TekScopes@...>
Sent: Monday, March 01, 2004 4:16 PM
Subject: RE: [TekScopes] 7S/7T Sampling System


Hi Dan,

Which 067-0587 are you talking about? the -02 is a 1GHz unit but the -01
is
slower (500 Mhz I think). I think the -00 is slower still. I ask becaue
that
will determine how fast the sampling heads need to be.

A 7T11A is much rarer and more expensive than a 7T11. Unless you need the
7T11A version (which is what a 7854 scope needs) there is nothing wrong
with
the 7T11. You will need a sampling head to go in the 7S11 such as an
S1/S2/S3/S3A/S4. Note the S1, S3, and S3A only go to 1GHz.

Have you considered a 7S14 instead of a 7T11/7S11/Sx. The 7S14 is often
overlooked because it is one of the original 7000 plugins. The 7S14 is a 1
GHz Dual Trace Sampling plugin with the sampling heads and a delayed
timebase all built in to a very easy to use self contained unit. It is
quite
nice. They can be had cheaply. It occupies two slots. So on a 4 slot
mainframe you can still use a real time amplifier and timebase at the same
time.

Dennis

-----Original Message-----
From: Dan Tulloss [mailto:dtulloss@...]
Sent: Monday, March 01, 2004 3:22 PM
To: 'TekScopes@...'
Subject: [TekScopes] 7S/7T Sampling System


Does anybody have a 7T11A or plain and a 7S11A or plain sampling system
that
is in good condition. Need a good one to do some 067-0587-XX's. Not
being
re-sold...for my use...saw that being asked this morning.

Thanks,
Dan Tulloss
Senior Metrologist
National Test Equipment, Inc.
760-639-1700
760-639-1799 Fax
www.nationaltestequipment.com





Yahoo! Groups Links










Yahoo! Groups Links
Craig Sawyers
 

I have read postings about using some fast Schotky
diodes in place of some of Tek's GaAs diodes but I have no personal
experience with this . . .
I did this with a defunct S3a 1GHz sampling probe. The brige was toast
(well, some of the diodes were leaky in reverse bias). Stan helped out by
looking up the spec of the original bridge diodes for me.

I found that the basic spec, most critically reverse leakage and capacitance
were matched rather well with Agilent microwave Schottkys, HSMS8202. These
are diode pairs in a single SOT23 surface mount package. By flipping one of
them over, and soldering the pair of pins one edge together you end up with
a bridge. Costs about 3 bucks.

Replacing the defunct bridge with this one worked perfectly - specification
of the resulting probe is exactly as it ought, full 1GHz bandwidth and
aberrations well within spec. I suspect that this approach would work well
with all the earlier samplers up to around 4GHz, including the S1 and S2.

The most obvious difference between GaAs, silicon junction and Schottky is
the foward voltage drop. GaAs is well over a volt, Si is about 0.7V, and
Schottky is about 0.3V. As I said I had no trouble, but potential problems
might arise with the reverse bias voltage and the magnitude of the strobe
signal. Usually these have a preset pot associated with them, and so can be
adjusted somewhat.

With the 1S1, the early GaAs bridge diodes were replaced later with Si ones
so it is certainly possible to do this on the 1S1.

The reason for GaAs was it was the only way to get speed in the early days
of samplers. Then silicon processing caught up, and GaAs production went
into a bit of a decline until LEDs came along, which are based on metallic
alloys of III/V semiconductors like GaAs. And now, GaAs is used in the very
fastest transistor technologies, the so called HEMT (high electron mobility
transistor) - these beasts still have useful gain at 150GHz plus.

Later (and much faster) sampling heads like the S4 and S6 used Schottky
diodes from day one. In fact to get the speed these are impressively tiny
to get the capacitance and lead inductance down - the junction is only 3um x
3um, and ridiculously easy to vapourise with static discharge, and event
that would ruin your day. The thick film, charge trap heads simply don't
lend themselves to being fixed on these fast samplers; if you zap them they
are scrap.

Other things that sampler fixers might like to bear in mind is that "back
diodes" (tunnel diodes with a very low peak current of about 100uA)are what
the microwave fraternity now confusingly calls tunnel diodes. They are
essentially used as zero bias detectors, and I think that close equivalents
to the BD4 could be found. Likewise the snap-off diodes that are used in
the strobe circuits are still available from the microwave component
suppliers, now called step-recovery diodes. Anyone wanting a browse through
this sort of arcana could look at

The only tricky thing is true tunnel diodes, for which there is no chance of
a commercially available equivalent.

Craig
Ashton Brown
 

Craig, thanks!

+11 Informative..

Your post encapsulates about a dozen questions I've had re refurb of the pure unobtainium stuff.
Printed!
It's Very nice to know that, with some precise fiddling - many of these can be resurrected.
(And thanks to Stan, repeatedly - for supplying the unobtainium Information!)
GaAs back with a vengeance, eh? 150 Ghz might get us 5000 Channels - with nothing watchable..

Two ears and a tail - {static-free, of course}


Ashton

Craig Sawyers wrote:

I have read postings about using some fast Schotky
diodes in place of some of Tek's GaAs diodes but I have no personal
experience with this . . .
I did this with a defunct S3a 1GHz sampling probe. The brige was toast
(well, some of the diodes were leaky in reverse bias). Stan helped out by
looking up the spec of the original bridge diodes for me.

I found that the basic spec, most critically reverse leakage and capacitance
were matched rather well with Agilent microwave Schottkys, HSMS8202. These
are diode pairs in a single SOT23 surface mount package. By flipping one of
them over, and soldering the pair of pins one edge together you end up with
a bridge. Costs about 3 bucks.

Replacing the defunct bridge with this one worked perfectly - specification
of the resulting probe is exactly as it ought, full 1GHz bandwidth and
aberrations well within spec. I suspect that this approach would work well
with all the earlier samplers up to around 4GHz, including the S1 and S2.

The most obvious difference between GaAs, silicon junction and Schottky is
the foward voltage drop. GaAs is well over a volt, Si is about 0.7V, and
Schottky is about 0.3V. As I said I had no trouble, but potential problems
might arise with the reverse bias voltage and the magnitude of the strobe
signal. Usually these have a preset pot associated with them, and so can be
adjusted somewhat.

With the 1S1, the early GaAs bridge diodes were replaced later with Si ones
so it is certainly possible to do this on the 1S1.

The reason for GaAs was it was the only way to get speed in the early days
of samplers. Then silicon processing caught up, and GaAs production went
into a bit of a decline until LEDs came along, which are based on metallic
alloys of III/V semiconductors like GaAs. And now, GaAs is used in the very
fastest transistor technologies, the so called HEMT (high electron mobility
transistor) - these beasts still have useful gain at 150GHz plus.

Later (and much faster) sampling heads like the S4 and S6 used Schottky
diodes from day one. In fact to get the speed these are impressively tiny
to get the capacitance and lead inductance down - the junction is only 3um x
3um, and ridiculously easy to vapourise with static discharge, and event
that would ruin your day. The thick film, charge trap heads simply don't
lend themselves to being fixed on these fast samplers; if you zap them they
are scrap.

Other things that sampler fixers might like to bear in mind is that "back
diodes" (tunnel diodes with a very low peak current of about 100uA)are what
the microwave fraternity now confusingly calls tunnel diodes. They are
essentially used as zero bias detectors, and I think that close equivalents
to the BD4 could be found. Likewise the snap-off diodes that are used in
the strobe circuits are still available from the microwave component
suppliers, now called step-recovery diodes. Anyone wanting a browse through
this sort of arcana could look at

The only tricky thing is true tunnel diodes, for which there is no chance of
a commercially available equivalent.

Craig




Yahoo! Groups Links

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