Topics

7K Fiber Optic Readout Holes WAS Vacuum forming 7K interface "covers"

 

Hi Ernesto,
Several others have explained the purpose of the 4 holes at the top of the rear panel on each 7000 plugin. It is not exactly true that there are no plugins that use these holes. From time to time there were special modified 7K plugins that used them.

In addition the 7A21N Differential (or Single Ended) Direct Access plugin for the 7900 mainframe, is a standard plugin listed in all of the Tek catalogs from 1972 to 1979 that used the holes.

The 7A21N drove the 7904 deflection plates directly to achieve a 350pSec risetime / 1GHz bandwidth before the 7104 became available. The single ended vertical sensitivity for a 7A21N in a 7904 is 4V/Div. The Differential sensitivity is ~10V/Div. The plugin used two of the holes to apply +DC and -DC voltage directly to the deflection plates to position the beam vertically on the screen.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David C. Partridge
Sent: Wednesday, April 22, 2020 1:05 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Vacuum forming 7K interface "covers"

They were put there during the design phase of the 7000 series when it was envisaged that the readout would use fibre-optics.

D.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ernesto
Sent: 22 April 2020 20:39
To: TekScopes@groups.io
Subject: Re: [TekScopes] Vacuum forming 7K interface "covers"

Since we are on the topic of the Tek 7000 main interface connectors, I noticed on top of the 38 side connectors there is an horizontal small row of places for four connector pins, coax. maybe.
All plugins have these spaces on their connectors, none that I see uses it. The holes are empty on the mainframe side too.

Does anyone know if Tektronix had had plans to expand the connectivity of the plugins but never got to do so?

Ernesto








--
Dennis Tillman W7PF
TekScopes Moderator

 

On Thu, Apr 23, 2020 at 12:39 AM, Dennis Tillman W7PF wrote:


In addition the 7A21N Differential (or Single Ended) Direct Access plugin for
the 7900 mainframe, is a standard plugin listed in all of the Tek catalogs
from 1972 to 1979 that used the holes.
I knew that I read about a specific module that uses these holes but couldn't think of it.
Thanks Dennis.

Raymond

 

Thank you Dennis,

This is very interesting application. On tekwiki is the manual of the 7A21N, and it shows the modifications of the mainframe to accommodate this direct access to the CRT plates.
There must have been quite a desperation to display a 1 Ghz signal on a CRT to justify such a modification and the labor to convert to this plugin and back to a regular 7900.
It must have required quite a powerful source of the 1 Ghz signal to provide the many volts into the 50 ohm load.

Ernesto

 

Hi Ernesto,
Tek has a long history of producing successful scopes where the input was directly coupled to the plates of the CRT/ The 519 was the first. It was introduced in 1961. I believe it was the very first scope capable of displaying a 1GHz signal. The government bought a lot of them since it was about the only way to capture the EMP from a nuclear detonation.

The 7A21N is an interesting plugin inside. It is even more interesting today since many of the high frequency principles it incorporated are now commonly used by hams when working with VHF and UHF frequencies.

It is surprisingly easy to generate pulses with any amplitude up to 100+ volts with sub-nanosecond risetime and fall time. The models 109 and 110 pulsers which Tek introduced in 1962 did just that. Their risetime was less than 250pSec (about 1.4GHz). Today a more practical way to do it is with a delay line connected to the collector of a bipolar transistor biased so it will avalanche. There is a TM500 plugin known internally as a Braatz Generator that does just this. It was first produced for limited internal use within Tek and known simply as the High Amplitude Pulse Generator. The original production run had a GR-874 connector on the front which was used to generate any length pulse you wanted by attaching the right length of 50ohm cable. The next version (same name) replaced the variable length pulse capability with a fixed length pulse by adding a coil of semi-rigid hard line inside the plugin. Each time a production run was made it was improved. Later it was released to the field as the 067-1094-99 calibration fixture. Finally it was given an official TM500 part number: PG109. I have the 4 versions I described. Unfortunately there are no manuals for it, only a partial schematic exists of one production version. I am not aware that a manual was ever produced for the PG109. I asked Dennis Braatz if he had any documentation but he didn't.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ernesto
Sent: Wednesday, April 22, 2020 8:25 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7K Fiber Optic Readout Holes WAS Vacuum forming 7K interface "covers"

Thank you Dennis,

This is very interesting application. On tekwiki is the manual of the 7A21N, and it shows the modifications of the mainframe to accommodate this direct access to the CRT plates.
There must have been quite a desperation to display a 1 Ghz signal on a CRT to justify such a modification and the labor to convert to this plugin and back to a regular 7900.
It must have required quite a powerful source of the 1 Ghz signal to provide the many volts into the 50 ohm load.

Ernesto





--
Dennis Tillman W7PF
TekScopes Moderator

 

On Thu, Apr 23, 2020 at 05:25 AM, Ernesto wrote:


It must have required quite a powerful source of the 1 Ghz signal to provide
the many volts into the 50 ohm load.
Hi Ernesto,
Tekwiki indicates a sensitivity of < 4 V/Div (SE), < 2 V/Div (Differential) with the 7A21N. That's not too bad at all. I find the deflection sensitivity of these CRTs surprisingly high.
AFAIK, the deflection sensitivity of the CRT in the 7104 is even higher, in V/cm.

Raymond

 

Hi Dennis, Raymond,

The manual of the 519 (available on BAMA) is a fascinating reading during these times of lock-down. Especially the section 3 on Applications.
On how they overcame the lack of amplification by taking a high quality photo of the screen and enlarging it, and observing it with a cross-feed manipulator under a microscope!

It must have been so interesting to work for Tektronix in those days! They were really pushing the state of the art.

Ernesto

Chuck Harris
 

The 513D, introduced around 1953 had a plexiglass cover over a
hole in the case that was there to allow direct connection to its
deflection plates.

-Chuck Harris

Dennis Tillman W7PF wrote:

Hi Ernesto,
Tek has a long history of producing successful scopes where the input was directly coupled to the plates of the CRT/ The 519 was the first. It was introduced in 1961. I believe it was the very first scope capable of displaying a 1GHz signal. The government bought a lot of them since it was about the only way to capture the EMP from a nuclear detonation.

The 7A21N is an interesting plugin inside. It is even more interesting today since many of the high frequency principles it incorporated are now commonly used by hams when working with VHF and UHF frequencies.

 

So that's why!

My 547 has a round opening on the left cover just in front of the vertical amplifier's connection to the vertical plates.
The opening is covered with a metal plate, of the same color of the cover.

So now I know what to do when I want to connect directly to the CRT plates!

Ernesto