Tektronix 7104 and 7D20 showstopping?


glennmhdk
 

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?


 

The Micro Channel Plate (MCP) was first used by Tek in the 7104 because of
its ability to increase the brightness of the trace. This is extremely
valuable when measuring single shot and/or high speed transients for
instance. The MCP is so good at this that a sub-nanosecond single shot event
is visible in broad daylight on its CRT. Before this scope it was almost
impossible to do this without darkening the room, using a scope hood, and
turning the brightness up to full which defocused the display.

However, the micro channels in this CRT are extremely sensitive and can be
burned out if subjected to too much beam current so Tek included circuitry
which integrated the beam current and shut down the beam if there was a
chance that the MCP was about to be damaged. This is the reason there is a
Limited Viewing Time LED and a Shutdown LED on the front panel of this
scope.

So, generally speaking, it is not a good idea to use any plugin that will
result in a lot of beam current in the 7104. This would include the logic
analyzers (7D01 and 7D02) since they generate multiple traces and/or
alphanumeric text which is displayed as a raster on the CRT. The raster is
refreshed constantly which results in a lot of CRT beam current. The 7D20
display is also raster based so its display generates lots of beam current
as well.

Yes, turning the intensity fully CCW (to off) will slow the accumulation of
MCP damage but what good is that? Why risk damage to a $30,000 scope by
using an inappropriate plugin in it? The optimal scope for the 7D20 is the
7603 because it has the biggest screen and because it has a limited
bandwidth so it can be had for very little money.

In general the 7603 is an outstanding scope for any of the plugins that are
not limited by the mainframe speed such as the 7D01/DF2 Hardware Logic
Analyzer, 7D02 Software Logic Analyzer, 7D12 and 7D13 DMM, 7D14 and 7D15
Counters, 7D20 Digitizer, 7S11/7T11 Sampler, 7S12 TDR, 7S14 Dual Trace 1GHz
Sampler, the 7Lxx Spectrum Analyzers, the 7CT1N Curve Tracer and the 7J20
Rapid Scan Spectrometer.

Dennis

-----Original Message-----
From: glennmhdk, Sent: Saturday, April 06, 2013 9:32 AM

Hi!
I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:
Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt
microchannel plate gain, permantly reducing the writing rate in the 7104.
What does this exactly mean? Can the intensity just be adjusted down to
counteract the incompatibility?


Paul Amaranth
 

I picked up a 7603r the other week for parts and now I've decided to fix it
up precisely for that reason. I'm putting together a 7s11/7t11 combo and
I have a 7ct1n which I really didn't care to use in my 7904. the 7603 really
does have a nice screen.

Paul

In general the 7603 is an outstanding scope for any of the plugins that are
not limited by the mainframe speed such as the 7D01/DF2 Hardware Logic
Analyzer, 7D02 Software Logic Analyzer, 7D12 and 7D13 DMM, 7D14 and 7D15
Counters, 7D20 Digitizer, 7S11/7T11 Sampler, 7S12 TDR, 7S14 Dual Trace 1GHz
Sampler, the 7Lxx Spectrum Analyzers, the 7CT1N Curve Tracer and the 7J20
Rapid Scan Spectrometer.

Dennis

-----Original Message-----
From: glennmhdk, Sent: Saturday, April 06, 2013 9:32 AM

Hi!
I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:
Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt
microchannel plate gain, permantly reducing the writing rate in the 7104.
What does this exactly mean? Can the intensity just be adjusted down to
counteract the incompatibility?
--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@AuroraGrp.Com | Unix & Windows


glennmhdk
 

--- In TekScopes@yahoogroups.com, "Dennis Tillman" <dennis@...> wrote:
...
burned out if subjected to too much beam current so Tek included circuitry
which integrated the beam current and shut down the beam if there was a
chance that the MCP was about to be damaged. This is the reason there is a
Limited Viewing Time LED and a Shutdown LED on the front panel of this
scope.

So, generally speaking, it is not a good idea to use any plugin that will
result in a lot of beam current in the 7104. This would include the logic
analyzers (7D01 and 7D02) since they generate multiple traces and/or
...
Dennis
...

Hi Dennis

Thanks for your elaborate answer.

-

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?

Page 19 (1-7) Readout display is continously displayed I assume:
http://bama.edebris.com/download/tek/7104/tek-7104.pdf

Page 36 "The location of each readout word is fixed"

Page 37 "3. Use minimum READOUT INTENSITY to display the readout"

On page 298 readout is "generated".

On page 307 Y-readout enters through p790 into vert-amp.

On page 315 X-readout enters through p790 into horiz-amp.

On page 323 I can see a "SCREEN I SENSE" but not some temporary MCP disable while readout?

Might it be "INT SENSE" that comes from page 291?

It can not be "AUX READOUT INT" that goes to page 301?

br,

Glenn


David DiGiacomo
 

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
It seems like you don't want to hear the answer to your question. It
is just stupid to use a 7D20 in a 7104. Don't do it.

The beam current warning/dimmer mechanism in the 7104 doesn't work
well enough to protect the CRT in all circumstances.
If you look at well-used 7104s, they generally have visible burn in
the readout area. This is more or less tolerable because it doesn't
affect the central area of the CRT, where we usually view waveforms.
The 7D20 gives you the opportunity to also burn the central area.


Craig Sawyers <c.sawyers@...>
 

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
It does. That is why the readout intensity knob has an off position, and a
pulsed mode that operates in several ways depending on a range of settings.
If you leave it operating continuously it will absolutely reduce the
sensitivity of the MCP at the readout positions. I have some images in the
pics section of Tekscopes that show an image of a single shot trace at
200ps/div from a TD pulser. Those were taken with a Tek C1002 CCD camera.
The slight graininess of the trace is due to the granular nature of
individual electrons striking the MCP before amplification. It is a helluva
tour de force of analogue scope engineering to do this.

Craig


 

On Sat, 06 Apr 2013 16:32:13 -0000, "glennmhdk"
<glenn.mh.dk@gmail.com> wrote:

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?
There was a discussion here not long ago about the fragility of the
MCP in the 7104.

My understanding is that the MCP is not only subject to damage from a
short term high intensity beam necessitating the intensity protection
circuits in the 7104, but it also suffers from limited life even under
normal conditions because even at low brightness, damage to each
individual micro channel is cumulative. The best way to extend its
usable life is to use the entire surface evenly and not leave traces
in the same position.


 

On Sat, 06 Apr 2013 18:53:32 -0000, "glennmhdk"
<glenn.mh.dk@gmail.com> wrote:

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
Over time the readout does cause damage to the MCP even at low readout
intensity but the damage is outside of the trace display area.

Page 19 (1-7) Readout display is continously displayed I assume:
http://bama.edebris.com/download/tek/7104/tek-7104.pdf

Page 36 "The location of each readout word is fixed"
The readout actually drifts around a little bit depending on
temperature and beam position. This is one of those traits that all
Tektronix analog readouts have that gives them character and is kind
of cute.

Page 37 "3. Use minimum READOUT INTENSITY to display the readout"

On page 298 readout is "generated".
It would not surprise me if Tektronix lowered the readout repetition
rate in the 7104 so it would not cause as much damage. The various
plug-in instruments which generate their own display would not include
this protection.


glennmhdk
 

--- In TekScopes@yahoogroups.com, David DiGiacomo <daviddigiacomo@...> wrote:

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
It seems like you don't want to hear the answer to your question.
Please bear over with me. I have never heard of microchannel before, and that 7104 has builtin readout seems to be the same CRT use as 7D20.

I am asking here because I would like to understand why. When some appearent inconsistency appear, I try to find out why.

It
is just stupid to use a 7D20 in a 7104. Don't do it.

The beam current warning/dimmer mechanism in the 7104 doesn't work
well enough to protect the CRT in all circumstances.
If you look at well-used 7104s, they generally have visible burn in
the readout area. This is more or less tolerable because it doesn't
affect the central area of the CRT, where we usually view waveforms.
The 7D20 gives you the opportunity to also burn the central area.
Thanks for your and Craigs answer.

-

Also found this about MCP:
http://en.wikipedia.org/wiki/Microchannel_plate_detector

Here it seems that MCP are many point-like (10um) electron multipliers.

This is completely new to me ;-)

br,

Glenn


glennmhdk
 

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:

On Sat, 06 Apr 2013 16:32:13 -0000, "glennmhdk"
<glenn.mh.dk@...> wrote:

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?
There was a discussion here not long ago about the fragility of the
MCP in the 7104.

My understanding is that the MCP is not only subject to damage from a
short term high intensity beam necessitating the intensity protection
circuits in the 7104, but it also suffers from limited life even under
normal conditions because even at low brightness, damage to each
individual micro channel is cumulative. The best way to extend its
usable life is to use the entire surface evenly and not leave traces
in the same position.
Hi David

I do understand that now.

But these MCP based CRTs have now been used for decades - and they are still bought and sold.

It is to some extend incredibly that they still work, even though they are so "fragile".

br,

Glenn


 

On Sat, 06 Apr 2013 19:51:55 -0000, "glennmhdk"
<glenn.mh.dk@gmail.com> wrote:

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:

On Sat, 06 Apr 2013 16:32:13 -0000, "glennmhdk"
<glenn.mh.dk@...> wrote:

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?
There was a discussion here not long ago about the fragility of the
MCP in the 7104.

My understanding is that the MCP is not only subject to damage from a
short term high intensity beam necessitating the intensity protection
circuits in the 7104, but it also suffers from limited life even under
normal conditions because even at low brightness, damage to each
individual micro channel is cumulative. The best way to extend its
usable life is to use the entire surface evenly and not leave traces
in the same position.
Hi David

I do understand that now.

But these MCP based CRTs have now been used for decades - and they are still bought and sold.

It is to some extend incredibly that they still work, even though they are so "fragile".
A lot of them do have damage to one extent or another but it is a case
of wearing out in specific areas of the MCP rather than outright
failure. The electron multiplication in those areas just goes down.

The 7834 and 7934 storage CRTs are also fragile and commonly show burn
marks in storage mode. On one of my 7834 oscilloscopes, you can see
the burn-in from the readout while my other 7834 looks great although
it has geometry distortion which I suspect was caused by UPS dropping
it.


glennmhdk
 

Also found these links about MCP usages:

7104, 7CT1N and 7904 saga:
http://tech.groups.yahoo.com/group/TekScopes/message/30133

7104 MCP degradation...:
http://tech.groups.yahoo.com/group/TekScopes/message/21240

Glenn


fiftythreebuick <ae5i@...>
 

They just don't want anything constantly written to the same parts of the screen for an extended length of time. Whether it's readout characters or a baseline or anything that just sits there. It "uses up" the useful life of the microchannel plate.

Plus, there is no need to put a 7D20 in a 7104. The 7104 is a speedburner that is intended to display high speed, low rep rate stuff and its capabilities are wasted on a 7D20. Or a spectrum analyzer or anything like that.

Now, if it's the only mainframe you have that you can run your 7D20 in, then you may have to do it, but I would keep the intensity to an absolute minimum and keep the display turned down/off when not actually being used.

I will say this though: 7603, 7623A and other mainframes can be had so cheap these days if you just shop around a bit that if I had a 7104, I would absolutely get another mainframe to run the 7D20 in. The 7104's capabilities are too precious/unique to waste....

Just my opinion....

Tom

--- In TekScopes@yahoogroups.com, "glennmhdk" <glenn.mh.dk@...> wrote:

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?


Chris Leyson
 

Let's not forget that this is a forum about classic CRT scopes. For an analogue scope it's the CRT that defines the scope's ultimate bandwidth and sensitivity followed down the chain by deflection amplifiers, channel switches, attenuators etc. the MCP CRT in the 7104 is a very special and delicate CRT really only to be used for high speed single shot measurements. A 7104 should really only be equipped with a pair of 7A29s a 7B15 and a 7B10. Fried electronics can be replaced but not MCP tubes.

Use any other mainframe for a 7D20 or if you're lucky get a 7D20T and use an X-Y monitor like a 620.

--- In TekScopes@yahoogroups.com, "fiftythreebuick" <ae5i@...> wrote:






They just don't want anything constantly written to the same parts of the screen for an extended length of time. Whether it's readout characters or a baseline or anything that just sits there. It "uses up" the useful life of the microchannel plate.

Plus, there is no need to put a 7D20 in a 7104. The 7104 is a speedburner that is intended to display high speed, low rep rate stuff and its capabilities are wasted on a 7D20. Or a spectrum analyzer or anything like that.

Now, if it's the only mainframe you have that you can run your 7D20 in, then you may have to do it, but I would keep the intensity to an absolute minimum and keep the display turned down/off when not actually being used.

I will say this though: 7603, 7623A and other mainframes can be had so cheap these days if you just shop around a bit that if I had a 7104, I would absolutely get another mainframe to run the 7D20 in. The 7104's capabilities are too precious/unique to waste....

Just my opinion....

Tom


--- In TekScopes@yahoogroups.com, "glennmhdk" <glenn.mh.dk@> wrote:

Hi!

I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:

Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt microchannel plate gain, permantly reducing the writing rate in the 7104.

What does this exactly mean? Can the intensity just be adjusted down to counteract the incompatibility?


Dave Daniel
 

I've never heard of the 7J20, but some searching on the web reveals it. Cool.

DaveD

On 4/6/2013 11:52 AM, Dennis Tillman wrote:
 

The Micro Channel Plate (MCP) was first used by Tek in the 7104 because of
its ability to increase the brightness of the trace. This is extremely
valuable when measuring single shot and/or high speed transients for
instance. The MCP is so good at this that a sub-nanosecond single shot event
is visible in broad daylight on its CRT. Before this scope it was almost
impossible to do this without darkening the room, using a scope hood, and
turning the brightness up to full which defocused the display.

However, the micro channels in this CRT are extremely sensitive and can be
burned out if subjected to too much beam current so Tek included circuitry
which integrated the beam current and shut down the beam if there was a
chance that the MCP was about to be damaged. This is the reason there is a
Limited Viewing Time LED and a Shutdown LED on the front panel of this
scope.

So, generally speaking, it is not a good idea to use any plugin that will
result in a lot of beam current in the 7104. This would include the logic
analyzers (7D01 and 7D02) since they generate multiple traces and/or
alphanumeric text which is displayed as a raster on the CRT. The raster is
refreshed constantly which results in a lot of CRT beam current. The 7D20
display is also raster based so its display generates lots of beam current
as well.

Yes, turning the intensity fully CCW (to off) will slow the accumulation of
MCP damage but what good is that? Why risk damage to a $30,000 scope by
using an inappropriate plugin in it? The optimal scope for the 7D20 is the
7603 because it has the biggest screen and because it has a limited
bandwidth so it can be had for very little money.

In general the 7603 is an outstanding scope for any of the plugins that are
not limited by the mainframe speed such as the 7D01/DF2 Hardware Logic
Analyzer, 7D02 Software Logic Analyzer, 7D12 and 7D13 DMM, 7D14 and 7D15
Counters, 7D20 Digitizer, 7S11/7T11 Sampler, 7S12 TDR, 7S14 Dual Trace 1GHz
Sampler, the 7Lxx Spectrum Analyzers, the 7CT1N Curve Tracer and the 7J20
Rapid Scan Spectrometer.

Dennis

-----Original Message-----
From: glennmhdk, Sent: Saturday, April 06, 2013 9:32 AM

Hi!
I have read about Tektronix 7D20 and it puzzles me why 7D20 can damage 7104:
Page 16 (2-16) writes 7104 can not use 7D20?:
http://bama.edebris.com/download/tek/7d20/tek-7d20.pdf

Why not? The text writes that 7D20 can cause permanent reduction in the crt
microchannel plate gain, permantly reducing the writing rate in the 7104.
What does this exactly mean? Can the intensity just be adjusted down to
counteract the incompatibility?



Don Black <donald_black@...>
 

Is there a concept book that describes the micro-channel tube and how it works?

Don Black.

On 07-Apr-13 5:23 AM, Craig Sawyers wrote:
 

> Then there is the internal 7104 readout display.
>
> Why does this not burn-out MCP?

It does. That is why the readout intensity knob has an off position, and a
pulsed mode that operates in several ways depending on a range of settings.
If you leave it operating continuously it will absolutely reduce the
sensitivity of the MCP at the readout positions. I have some images in the
pics section of Tekscopes that show an image of a single shot trace at
200ps/div from a TD pulser. Those were taken with a Tek C1002 CCD camera.
The slight graininess of the trace is due to the granular nature of
individual electrons striking the MCP before amplification. It is a helluva
tour de force of analogue scope engineering to do this.

Craig



 

The best I have found is the Electronic Design article which is linked
here:

http://www.vintagetek.org/tag/micro-channel-plate-crt/

On Sun, 07 Apr 2013 14:17:59 +1000, Don Black
<donald_black@bigpond.com> wrote:

Is there a concept book that describes the micro-channel tube and how it
works?

Don Black.

On 07-Apr-13 5:23 AM, Craig Sawyers wrote:

Then there is the internal 7104 readout display.

Why does this not burn-out MCP?
It does. That is why the readout intensity knob has an off position, and a
pulsed mode that operates in several ways depending on a range of
settings.
If you leave it operating continuously it will absolutely reduce the
sensitivity of the MCP at the readout positions. I have some images in the
pics section of Tekscopes that show an image of a single shot trace at
200ps/div from a TD pulser. Those were taken with a Tek C1002 CCD camera.
The slight graininess of the trace is due to the granular nature of
individual electrons striking the MCP before amplification. It is a
helluva
tour de force of analogue scope engineering to do this.

Craig


glennmhdk
 

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:
...

It would not surprise me if Tektronix lowered the readout repetition
rate in the 7104 so it would not cause as much damage. The various
plug-in instruments which generate their own display would not include
this protection.
Hi group

From:
http://www.vintagetek.org/wp-content/uploads/2011/10/7104-Springer-article-email-res.pdf
It can be read on pdf-page 3, that the MCP gain can be varied by changed the MCP bias voltage.

At page 323 the MCP output voltage can be varied by (R1720 MCP gain) and by "INT SENSE P1705 (P1705 hard to read)". R1720 can not be controlled at the front, so it must some sort of trimpot:
http://bama.edebris.com/download/tek/7104/tek-7104.pdf

-

Regarding how the CRT works.

How can it be, that the input MCP potential is only +2265V? (grounded relative to the cathode at -2265V). Even though the anode voltage is some multipla of 2400V, the MCP "intercepts" the high anode potential? This ought to mean, that the electrons are only accelerated by +2265V - and not e.g. by 5*2400V+2265V (do not know if it is exactly 5)?

Only after the MCP, are the electrons fully accelerated. But the electron beam was focused before the MCP? This appearently do not make sense? Do somebody know how this works or can point to some page?

Glenn


Craig Sawyers <c.sawyers@...>
 

==========================
Is there a concept book that describes the micro-channel tube and how it
works?

Don Black.
==========================

Hi Don

Don't think so. But the concept of using a multi-channel plate for electron
multiplication actually comes from military image intensifier tubes. In
fact I got to know the British guy who developed the prototype MCP's for Tek
, now working for Photonis in Brive, France. Ray was working at Mullard at
the time, and the technology was transferred to Tek eventually. At that
time, and pretty much still, this was the largest MCP ever made.
Generically, they are made by using two types of glass - a leachable core,
and a non-leachable cladding. These are around 6mm solid for the core and
10mm tube with a 6mm hole for the cladding. Length is around 50cm to 100cm.
The fit is precision, and the individual rods and tubes are expensive.
These are assembled into a stack maybe 50mm in diameter and put in a fibre
drawing machine. The resulting rod is cut and re-stacked, and re-drawn, and
the process repeated. Eventually a large number of these approx 5mm solid
preforms are assembled by hand into a jig, inserted into a furnace and fused
together to make a solid block the final size of the MCP with the correct
number of pores. This preform is then diamond sawn into the correct
thickness slices. With the Tek MCP the slices are taken at a bias angle of
about 23 (I think it was that) degrees, so electrons can never go straight
through - they always suffer multiple reflections from the inside of the
tiny pores. After slicing, the solid slices are then immersed in
exceptionally controlled conditions in etchant to remove the leachable
parts.

For a "regular" size MCP, these are circular with maybe 25mm to 50mm
diameter. The Tek one was 100mm x 80mm.

For what it is worth the same sort of technology was used to make flexible
fibre image bundles in medical endoscopes (before the days of video
endoscopes), except this time there were three glasses. An inner and outer
of different refractive indices (ie the normal sort of optical fibre) made
of non-leachable glasses, and an outer cladding of leachable glass. Reverse
of the MCP process (stack-draw-cut-restack-etc, then cut stack fuse), after
masking the ends to prevent leaching, what you ended up with were solid
stubs that you could form an image on at one end and look at with an
eyepiece at the other, but with every fibre individual and floppy in the
metre of so between.

Craig


Craig Sawyers <c.sawyers@...>
 

The best I have found is the Electronic Design article which is linked
here:

http://www.vintagetek.org/tag/micro-channel-plate-crt/
Thanks for that link - an exceptionally interesting article.

Craig