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Re: Early 465 CRT "mesh" or "Post Accelerator Grid".

 

On Tue, Apr 6, 2021 at 02:01 AM, Dave Peterson wrote:


So why the discrepancy with early, yet changed, service manual documentation?
What's the history of the Post Accelerator Grid? When was it introduced?
Hi Dave,
The expansion mesh is a type of electric lens in a CRT that provides increased deflection sensitivity. It had been used in several 7000-series CRT's predating the 465.

I have several reasons to be convinced that the 465 used an expansion mesh from the beginning:

1. Its influence on the design, features, and functioning of the 'scope is such that it would be part of the original design brief, not something that would easily be added in a later version of the same model. It takes its place as one of the anodes in the CRT and it's dome-shaped, hollow side toward the tube socket.

2. The voltages on CRT pin 12 in the sub-250k S/N's and those above 250k are quite comparable, both being -150V nominally.

Looking at the SMs, I see a sub-250k version (your version 070-1330-00, with M20, 159/573 change sheets), where one of the main changes is the substitution of a discrete vertical amplifier, replacing the IC-version. That had to be done because of a shortage of vertical output IC's.
According to the base version SM, a CRT 154-0676-00 was used up to S/N B010499 (B010100 often was the lowest Beaverton S/N), which was followed by 154-0676-05, starting from S/N B010500.
The first print 250k+ SM (070-1861-00, august '74) mentions CRT model 154-0676-10 from S/N 250k and 154-0731-00 from S/N B274371. The latter model probably produces a sharper picture. It was also used in the 465B successor to the 465.

This brings me to
3. It would have been quite unusual for Tek to use the same main model designation (154-0676) both for a meshless version and a version with an expansion mesh. Differences in mesh construction and layout are thinkable though.

Raymond


Early 465 CRT "mesh" or "Post Accelerator Grid".

Dave Peterson
 

I made a casual comment in another thread that the early (pre SN B250000) 465 did not have a "mesh" in it's CRT. This was based on it missing in the CRT schematic diagram in my early 465 Service Manual, 070-1330-00.

I found this difference when following Jeff Dutky's 475 debug saga. That's when I realized my SM was too early, and I learned the difference between early and "SN B250000 and up" 465s. I've since acquired a "SN B250000 and up" Service Manual, 070-1861-00 (First Printing AUG 1974). It does include the "mesh" circuit in the CRT diagram/schematic.

My earlier SM includes several pages of yellow/orange change information. I don't know the print date of the manual, nor of the change sections. The change section does include the identifier "M20,159/573". But I have no idea of its meaning or utility. Changes include vertical and horizontal amplifiers and trigger circuits. It also includes a change to the CRT circuit with a diagram including the T1420 transformer and CRT. Again, no "mesh" circuit and grid.

I am new to this hobby, getting my first scope back in November last year. So I'm trying to learn some of the differences in this model of scopes since this is the model I am most familiar with. My interests and understanding are expanding with experience, but my focus is on the 465 in particular.

Raymond, you said that the early (pre SN 250K) 465s definitely do have a "mesh" in their CRTs, and I don't doubt you. My "expertise" in Tektronix oscilloscope CRTs extends to what I've seen on YouTube videos.

The "Post Accelerator Grid" does seem a significant component of the 465 CRT and I'm very curious as to this discrepancy between the early service manual and changes and your observation. As you also noted, the Tek Wiki includes a pointer to an early document dated 11-9-72, "Tektronix T4650 Test Specifications", which refers to pin 12 as the "Post Accelerator Grid". So it seems it was intended as early as that date. I can also see that my SN177xxx scope does have the associated circuitry. Even a "12" silk screened on the A9 board at the confluence of CR1427, C1427, R1427, ... and a wire that goes into the bundle to the rear connector of the CRT. But my "early" scope is a hodge-podge of early and later parts.

So why the discrepancy with early, yet changed, service manual documentation? What's the history of the Post Accelerator Grid? When was it introduced?

I find myself using both early and late manuals while working my this earlier scope. Especially on the vertical amp. The early document's change section more closely matches the vertical amp I have. I keep the early manual as it does seem to help with the earlier scope in some instances. Seems with regards to the CRT schematic it is woefully out sync with scopes in the field?

Thanks,
Dave


Sphere's 2021 Stuff Season is officially open....

 

Our on-line Stuff Season Event at Sphere Research Corp. is now fully stocked and open, you can see it all here: https://www.sphere.bc.ca/test/stuffday.html

It will run through the summer, and will get updated daily. Our plan is to post new items and remove sold ones on a daily basis, as photos and text are available. Lots of new categories in addition to Tek, HP and Fluke, such as Audio, R+D Magic, Power Supplies and $1, $2 and $5 stuff. At the bottom of the page, we have a huge clear-out of Tek, HP and standard CRTs of all kinds, there are some real bargains there, and we can really use the space they are taking up!.

This event makes up for our not being able to host our annual Stuff Day event here, thanks to COVID restrictions, and also makes it possible for people farther away to have fun at the event. Our goal this year is to move at least 2 tons of parts and equipment, so a LOT of things will go through the site. No matter how obscure your interests are, there will be something you will enjoy.

This on-line effort makes up for our not being able to host our annual Stuff Day event here, thanks to COVID restrictions, and also makes it possible for people much farther away to have fun at the event. Our goal this year is to move at least 3 tons of parts and equipment, so a LOT of things will go through the site. No matter how obscure your interests are, there will be something you will enjoy.

We are doing our best to put hard to find service items on the page at prices attractive enough to make it worthwhile to fix older gear, and we are happy to take REQUESTS for things you want to see there.

There is a FREE STUFF section at the bottom for items we had time to photograph, but we ALSO add a bag of free parts goodies to everybody's order if it will fit in their shipping space and weight allowance.
I hope you will take some time to browse through the event this year. Thanks to everyone that has done so in the past, we actually cleared out one entire off-site storage building, and got a lot of aisles cleared out of stacked overflow stuff, that is real progress! About 2,500 square feet of stuff still to go...

stay safe and all the best,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.
https://www.sphere.bc.ca/test/index.html


Re: 465 Missing a Few Components

Stephen
 

On Mon, Apr 5, 2021 at 12:00 PM, Dave Peterson wrote:


Thanks for the pointer Raymond.

I think this topic deserves a new and separate thread. I find the early 465
history fairly interesting. Tek was clearly interested in getting this scope
out on the market, and encountered a lot of changes between early releases and
later. My early service manual has a large change section at the rear, and I
seem to have as many variants of vertical amp board as I do 465 scopes. With
associated schematics and cal procedures.

I'll post a new message thread asking for clarification on the early 465 CRT
"mesh" pin 12.

Dave
Agreed,

Did you see the B-Sweep cams I posted in the photos? How do they compare to early ones that you mentioned? Same for the grounded attenuators. A picture is also available in the folder.


Re: 465 Missing a Few Components

Stephen
 

Raymond,

I finally saw it. Well hidden indeed!!!

It’s exactly the same as your picture:
670-2233- (and nothing...)

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0


Re: 465 Missing a Few Components

Dave Peterson
 

Thanks for the pointer Raymond.

I think this topic deserves a new and separate thread. I find the early 465 history fairly interesting. Tek was clearly interested in getting this scope out on the market, and encountered a lot of changes between early releases and later. My early service manual has a large change section at the rear, and I seem to have as many variants of vertical amp board as I do 465 scopes. With associated schematics and cal procedures.

I'll post a new message thread asking for clarification on the early 465 CRT "mesh" pin 12.

Dave

On Monday, April 5, 2021, 03:35:52 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

On Tue, Apr  6, 2021 at 12:15 AM, Dave Peterson wrote:


BTW Raymond, I have the same book: 070-1330-00 with the same diagram. This is
the book to which I'm referring when I say the CRT does not appear to have a
mesh circuit. Thus my conclusion. Not the only discrepancy I've found between
this book and my SN177xxx.
The mesh is connected to pin 12 in the CRT socket. You can see it mentioned by its name in the CRT circuit dwg in the >=250000 SM.
The test specification of the T4650 CRT, which the 465 entry in Tekwiki links to, mentions it as Post Accelerator Grid and uses the word "mesh" on page 2. That document is from November 1972, long before the first printing 250000 SM, which is dated August 1974.

Raymond


Re: 465 Missing a Few Components

 

On Tue, Apr 6, 2021 at 12:47 AM, Raymond Domp Frank wrote:



But there is nothing there. The only number is the one I took a picture
of.
The board date is 1971. There is nothing else.
Photo from SM added. Number is in same location on one of my parts donkey
boards.

https://groups.io/g/TekScopes/photo/262670/0?p=Created ,,,50,2,0,0
Cleverly hidden underneath the "Invert" button shaft...

Raymond


Re: 465 Missing a Few Components

 

On Tue, Apr 6, 2021 at 12:34 AM, Stephen wrote:


But there is nothing there. The only number is the one I took a picture of.
The board date is 1971. There is nothing else.
Photo from SM added. Number is in same location on one of my parts donkey boards.

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0

Raymond


Re: 465 Missing a Few Components

Stephen
 

On Mon, Apr 5, 2021 at 11:30 AM, Dave Peterson wrote:


Stephen,
It looks like you have Q1534 reversed with Q1546 in the close-up you have
annotated.
Tracing that middle via, the "C" (if the silk screen is even there - ouch!),
of the nearer heat sinked transistor, should go to C1542 over by CR1541. It's
the center pin of the rear-most, outer-most big PS can capacitor.
Dave
You are absolutely right. However, these 3 power transistors are the same parts anyway (MJE2801).
But Q1546 and Q1566 are “selected”,...


Re: 465 Missing a Few Components

 

On Tue, Apr 6, 2021 at 12:15 AM, Dave Peterson wrote:


BTW Raymond, I have the same book: 070-1330-00 with the same diagram. This is
the book to which I'm referring when I say the CRT does not appear to have a
mesh circuit. Thus my conclusion. Not the only discrepancy I've found between
this book and my SN177xxx.
The mesh is connected to pin 12 in the CRT socket. You can see it mentioned by its name in the CRT circuit dwg in the >=250000 SM.
The test specification of the T4650 CRT, which the 465 entry in Tekwiki links to, mentions it as Post Accelerator Grid and uses the word "mesh" on page 2. That document is from November 1972, long before the first printing 250000 SM, which is dated August 1974.

Raymond


Re: 465 Missing a Few Components

Stephen
 

I understand, Raymond.

But there is nothing there. The only number is the one I took a picture of.
The board date is 1971. There is nothing else.

Also, the shield on the attenuators, do not have the long “S” shaped ground spring that connects to the case.
Instead they have 2 wires directly soldered to the board.

Pictures here:
https://groups.io/g/TekScopes/photo/262670/1?p=Created,,,50,2,0,0”

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0“

B-Sweep cams:
https://groups.io/g/TekScopes/photo/262670/3?p=Created,,,50,2,0,0”

Thanks for the board pictures with the labeling, Raymond. That helps a lot.


Re: 465 Missing a Few Components

Dave Peterson
 

Stephen,
It looks like you have Q1534 reversed with Q1546 in the close-up you have annotated.
Tracing that middle via, the "C" (if the silk screen is even there - ouch!), of the nearer heat sinked transistor, should go to C1542 over by CR1541. It's the center pin of the rear-most, outer-most big PS can capacitor.
Dave

On Monday, April 5, 2021, 03:06:09 PM PDT, Stephen <stephen.nabet@gmail.com> wrote:

Thanks for the tip Dave.

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0”

Let’s see if that works.

I’m definitely going through and check all the solder joints.  Some look quite cold...


Re: 465 Missing a Few Components

 

On Tue, Apr 6, 2021 at 12:00 AM, Stephen wrote:


Indeed. I also found that, European made models are often closer to higher
serial numbers in the US.
Board serial number is GC-2773-06. That’s all there is that I can see.
The 465 was designed in the USA and first produced there. In those situations, the early foreign numbers more closely relate to later USA numbers.
The board model no. probably sits between the Beam Finder switch and the front of the 'scope. It definitely is of the form "670-xxx-yy".

Raymond


Re: 465 Missing a Few Components

Dave Peterson
 

BTW Raymond, I have the same book: 070-1330-00 with the same diagram. This is the book to which I'm referring when I say the CRT does not appear to have a mesh circuit. Thus my conclusion. Not the only discrepancy I've found between this book and my SN177xxx.

Oh, and I just remembered another significant mismatch between pre & post SN250K: The B-sweep switch cam is different. I have an extra early cam if anyone needs one!

Dave

On Monday, April 5, 2021, 03:06:11 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

I added a photograph of the relevant part of the Main Board (fig. 7-12 in the SM, 070-1330-00),
here:

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0

When using the web interface, just make sure you include the numbers and commas at the end of the link - or use mail messages.

Raymond


Re: 465 Missing a Few Components

 

On Tue, Apr 6, 2021 at 12:06 AM, Raymond Domp Frank wrote:


I added a photograph of the relevant part of the Main Board (fig. 7-12 in the
SM, 070-1330-00),
here:
Much more useful (SM figure 7-21):

https://groups.io/g/TekScopes/photo/262670/4?p=Created,,,50,2,0,0


Raymond


Re: 465 Missing a Few Components

Dave Peterson
 

Could you clarify Raymond?

Why does the early SM that I have, have no circuitry from the transformer nor CRT mesh pin (pin 12) in the "CRT CIRCUIT" diagram?

I'm not doubting what you say - you clearly have experience in these matters. As I noted, I haven't looked into this in detail on the scope I have (SN177xxx). What is the history? Why not in the manual if all scopes have it? I'm trying to learn these details, so you're insight is appreciated.
Dave

On Monday, April 5, 2021, 02:54:34 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

On Mon, Apr  5, 2021 at 11:44 PM, Dave Peterson wrote:


The early 465s don't have a mesh in the tube according to my SMs.
Oh yes, they definitely do.

I don't know if my SN<250K does or doesn't.
So yes, it does. The mesh not only increases the CRT's deflection sensitivity, it unfortunately also increases the spot size. A lot of development has been done after these first efforts. Later versions of the 465 used modified CRT's, resulting in slightly sharper traces. Other improvements helped that.

Raymond


Re: 465 Missing a Few Components

 

I added a photograph of the relevant part of the Main Board (fig. 7-12 in the SM, 070-1330-00),
here:

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0

When using the web interface, just make sure you include the numbers and commas at the end of the link - or use mail messages.

Raymond


Re: 465 Missing a Few Components

Stephen
 

Thanks for the tip Dave.

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0”

Let’s see if that works.

I’m definitely going through and check all the solder joints. Some look quite cold...


Re: 465 Missing a Few Components

Stephen
 

On Mon, Apr 5, 2021 at 10:45 AM, Raymond Domp Frank wrote:


On Mon, Apr 5, 2021 at 11:23 PM, Stephen wrote:


It’s a European made scope, so the serial number starts with 70xxxxx.
Actually, Tektronix had factories in three locations in Europe:
Units with serial numbers starting with 1 were made in Guernsey (Channel
Islands)
Units with serial numbers starting with 2 were made in London (UK)
Units with serial numbers starting with 7 were made in Heerenveen
(Netherlands)

Unfortunately, there is no way to cross-reference serial numbers between
factories; each used their own serialization.

Have a look for the main board number; it should have the form of 670-xxxx-yy
and is usually located near the Beam Finder switch.

Raymond
Indeed. I also found that, European made models are often closer to higher serial numbers in the US.
Board serial number is GC-2773-06. That’s all there is that I can see.

https://groups.io/g/TekScopes/photo/262670/0?p=Created,,,50,2,0,0

If the link doesn’t work, scroll through the pictures.

Also, that resistor and solder joint next to it, don’t look to good. They seem to have been to hell and back...


Re: 465 Missing a Few Components

 

On Mon, Apr 5, 2021 at 11:44 PM, Dave Peterson wrote:


The early 465s don't have a mesh in the tube according to my SMs.
Oh yes, they definitely do.

I don't know if my SN<250K does or doesn't.
So yes, it does. The mesh not only increases the CRT's deflection sensitivity, it unfortunately also increases the spot size. A lot of development has been done after these first efforts. Later versions of the 465 used modified CRT's, resulting in slightly sharper traces. Other improvements helped that.

Raymond

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