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


 

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


Dave Peterson
 

Nice! Thank you Raymond!

I was trying to decipher the significance of the tube part numbers in the manuals. Kind of goes back to my original concern and wondering about early 465 restoration: if the tube is gone would it be pretty much it for that scope because of the mesh? I see now why you find it highly unlikely. And it is reassuring to consider that an early scope can be restored with a later tube. Is this true with the change from -00 to -05 and then -10? Are these differences just small internal changes that don't affect the gross connectivity and operation?

I'm still - need a word here - unsettled? That the early manuals have no mesh circuit drawn. When I was looking at my early scope I was able to find in the later manual's board diagram the associated components, and then find them on the board. Also an interesting tid-bit is that the printing for the components on the board diagram, CR1427, R1428, and VR1428, are of different weight and look added on. Looking in the earlier manual's board diagram I do not see these components. Unfortunately the earlier manual diagrams don't include the part indexing that the later manual does. I'm very curious to find out if Stephen's 070465 scope has them - and the wire going to the CRT connector (pin 12 presumably). It must have something! His is the only example I've come across - not that I've come across a lot - that is constructed like the board diagram in the earlier manual. Specifically the location of C1549 in his case. I also found quite a difference in layout surrounding C1419, the oft failed filter cap that causes F1419 to blow.

When you were asking him about his board part number you seemed to have a similar board at hand? Do you? How does this earlier board drive pin 12?

Thanks again for the detailed info and context Raymond. It's good to know these particulars as I gain experience with these scopes.
Dave

On Monday, April 5, 2021, 06:13:21 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

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


 

On Tue, Apr 6, 2021 at 03:54 AM, Dave Peterson wrote:


Are these differences just small internal changes that don't affect the gross
connectivity and operation?
Yes, I'm quite convinced that is so.

I'll have a look at your other points tomorrow (hopefully), since it's 4 AM where I live (continental Western Europe) and it's time for a nap...

Raymond


Stephen
 

Dave,

I don’t seem to find your last message. But you were asking me something regarding removing the back to take a picture of the CRT pins, correct?
Could you refresh my memory?


 

On Tue, Apr 6, 2021 at 03:54 AM, Dave Peterson wrote:


When you were asking him about his board part number you seemed to have a
similar board at hand? Do you? How does this earlier board drive pin 12?
I have one board left. It looks very old and is quite dirty. It carries ref. no. 670-2233, like Stephen's.
The HV multiplier has date code 7341, earliest component dates are 7337, latest "originals" are 7431, so it's probably a 250000-plus board.
It has the ganged focus tracking pot and has the mesh components (C/CR/R1427, C/R1428 and C1418/1419 (one dipped tantalum cap 47uF/35V) in the locations as indicated in the 250000-plus SM 070-1861-00.
CRT pin 12 has been in use and connected and probably connected to C1427.

Raymond


Dave Peterson
 

Hi Stephen,

No, I was asking about components underneath the HV cover on the bottom of the scope. It looks from your pictures that you already have it off - I can see one of the hex stud posts next to Q1566. The last remaining power supply driver that's mounted to the heat sink.

I was wondering if you can see what's driving the wire to pin 12 of the CRT. The early 070-1330-00 service manuals do not appear to have the necessary components in the board diagrams for A9. See the photos I've added to your album (not posting links since they seem to be causing problems and potentially more confusion). This is the rear of the A9 board adjacent to the vertical pre-amp assembly, opposite the power supply side (left and right are confusing depending on orientation of the scope - looking at A9 the scope is upside-down).

I'm curious what your board has. In researching your original question I found that, at least with regards to C1549, your A9 board is constructed per the early service manual board diagram. That made me wonder what the mesh driver circuit on your board looks like, since the early service manual does not include any mesh driver schematic nor board components.

My original and fundamental concern is/was the uniqueness of early 465 CRTs. But it seems the early 465 CRTs should have a mesh, and therefore are interchangeable with later 465 CRTs. My conclusion, based on the location of C1549, was that this appeared to be a very early 465 and that it might not have the mesh/circuits. Presuming that yours does have the components CR1427, R1427, and VR1428 as indicated in the later service manuals, then you have an A9 board that is a hybrid/intermediate variation that includes the "old" C1549 location and "new" CR1427/R1427/VR1428 installations. It would make for an interesting documentation of such a board as it does not seem to be documented in either service manual.

Pardon the thread theft, and I'm sure I've flogged this dead horse enough.
Dave

On Tuesday, April 6, 2021, 10:28:56 AM PDT, Stephen <stephen.nabet@gmail.com> wrote:

Dave,

I don’t seem to find your last message.  But you were asking me something regarding removing the back to take a picture of the CRT pins, correct?
Could you refresh my memory?


Stephen
 

C1427, R1427??
I don’t see them on the pictures you posted.... 🤷‍♂️
Look at the one I’m posting right now


 

On Tue, Apr 6, 2021 at 09:55 PM, Dave Peterson wrote:


I was wondering if you can see what's driving the wire to pin 12 of the CRT.
The early 070-1330-00 service manuals do not appear to have the necessary
components in the board diagrams for A9.
Sure it does.
We're talking about VR1434 and C1434 in the CRT schematic.
Figure 7-17 shows them just to the right of the space between the long ceramic combined resistor R1431 and C1404, right above C1404 and CR1404, printed diagonally.

Raymond


satbeginner
 

Hi all,

A while back I transplanted a 465 CRT to a 2235, and in that one too I needed to add the Pin12 wire and components to provide the appr. 110VDC.

Like Raymond said, just one resistor, diode and capacitor.

Saludos,

Leo


Dave Peterson
 

That's what I was looking for.

Yeah, exactly, the early service manual doesn't include those components, and those are the components that are supposed to drive pin 12 of the CRT.

Your picture shows your board matches the early service manual and does not include CR1427, R1428, and VR1428 (note: previous message called out R1427 instead of R1428).

See the picture I just added. Your board doesn't have these. Interesting. Talk about missing parts!

Dave

On Tuesday, April 6, 2021, 02:16:37 PM PDT, Stephen <stephen.nabet@gmail.com> wrote:

C1427, R1427??
I don’t see them on the pictures you posted....  🤷‍♂️
Look at the one I’m posting right now


Dave Peterson
 

Eureka! There it is, right in front of me.

Dave

On Tuesday, April 6, 2021, 02:26:57 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

On Tue, Apr  6, 2021 at 09:55 PM, Dave Peterson wrote:


I was wondering if you can see what's driving the wire to pin 12 of the CRT.
The early 070-1330-00 service manuals do not appear to have the necessary
components in the board diagrams for A9.
Sure it does.
We're talking about VR1434 and C1434 in the CRT schematic.
Figure 7-17 shows them just to the right of the space between the long ceramic combined resistor R1431  and C1404, right above C1404 and CR1404, printed diagonally.

Raymond


Dave Peterson
 

And the wire is the red striped one in Stephens picture that runs in front of the R1431 resistor over to the bundle, and then up to the CRT.

I see now what they did, and I was distracted by the relocation of the circuitry, not that it was missing. And the CRT tube schematic was updated to be a little more explicit.

And now I'm that much more clear on the early/late difference. And still find it interesting that my scope SN B177xxx is the later layout, not the earlier. Perhaps coinciding with CRT part number change at SN B010500? But that's not necessarily so either.

Dave

On Tuesday, April 6, 2021, 02:50:06 PM PDT, Dave Peterson via groups.io <davidpinsf=yahoo.com@groups.io> wrote:

Eureka! There it is, right in front of me.

Dave

    On Tuesday, April 6, 2021, 02:26:57 PM PDT, Raymond Domp Frank <hewpatek@gmail.com> wrote:

On Tue, Apr  6, 2021 at 09:55 PM, Dave Peterson wrote:


I was wondering if you can see what's driving the wire to pin 12 of the CRT.
The early 070-1330-00 service manuals do not appear to have the necessary
components in the board diagrams for A9.
Sure it does.
We're talking about VR1434 and C1434 in the CRT schematic.
Figure 7-17 shows them just to the right of the space between the long ceramic combined resistor R1431  and C1404, right above C1404 and CR1404, printed diagonally.

Raymond


Stephen
 

On Tue, Apr 6, 2021 at 10:44 AM, Dave Peterson wrote:


That's what I was looking for.

Yeah, exactly, the early service manual doesn't include those components, and
those are the components that are supposed to drive pin 12 of the CRT.

Your picture shows your board matches the early service manual and does not
include CR1427, R1428, and VR1428 (note: previous message called out R1427
instead of R1428).

See the picture I just added. Your board doesn't have these. Interesting. Talk
about missing parts!

Dave
So I guess this one is a pretty early model then.
In my other thread, I was asking about “missing parts”, referring to those that had been obviously scavenged, not to those that had never been there to begin with. 😬

But I think I’m gonna leave it as is (If it’ll even work...), and not convert it to a later model.
I’ll replace the missing parts and see if the CRT is even working on this thing, who knows...


Stephen
 

BTW, you’re talking about “mesh” this, and “mesh” that...
I don’t even know what that is. Could someone please enlighten me?
What does it mean?


 

On Tue, Apr 6, 2021 at 11:58 PM, Dave Peterson wrote:


And the wire is the red striped one in Stephens picture that runs in front of
the R1431 resistor over to the bundle, and then up to the CRT.
Time to give away another secret:
The wire actually is white, with a brown and a red stripe. Guess why?

Raymond


Michael W. Lynch
 

On Tue, Apr 6, 2021 at 05:05 PM, Stephen wrote:


BTW, you’re talking about “mesh” this, and “mesh” that...
I don’t even know what that is. Could someone please enlighten me?
What does it mean?
Stephen,

Here is a link to an excellent article on the Vintage TEK site. This is by Peter Keller and explains the mesh and its function.

https://vintagetek.org/wp-content/uploads/2017/07/Tek-CRT-History-Keller-Dec-2007-Pt6.pdf

Hope this helps.

--
Michael Lynch
Dardanelle, AR


Stephen
 

On Tue, Apr 6, 2021 at 11:25 AM, Raymond Domp Frank wrote:

Time to give away another secret:
The wire actually is white, with a brown and a red stripe. Guess why?

Raymond
Because the designer was colorblind?? 🤷‍♂️


Stephen
 

Thank you Michael! 😊


 

On Wed, Apr 7, 2021 at 12:00 AM, Stephen wrote:


But I think I’m gonna leave it as is (If it’ll even work...), and not
convert it to a later model.
You can't do without any voltage on pin 12. See Satbeginner's message.
A bias voltage of about 150V is needed or all electrons will just land on the grid and die/charge it.
IOW: If the image is fine without a bias, there probably isn't an expansion mesh in your CRT...

Raymond