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Don't forget that PC fans are good and bad. If you want something good
buy Noctua, or, in a pinch, BeQuiet.

On Wed, Apr 7, 2021 at 2:28 AM durechenew via groups.io
<durechenew@...> wrote:

Thank you, Raymond and Siggi, for taking the time to answer to this post. Unfortunately the motor of the blower is beyond repair (back side bushing is completely broken), therefore the whole stuff must be replaced. I've seen a blower that might be appropriate for the purpose, beside the obvious (and, as Siggi said, undesired) regular fan. I'm quite aware of all the issues (I recently put a fan on a 2235 and, yes, I had to go from 8V to 5V - for a 12V motor - to get a decent noise. For fan I was considering making some additional holes in the back cover to allow for easier flow; but no decision yet.
TT

On Wed, Apr 7, 2021 at 02:54 AM, Raymond Domp Frank wrote:

I thought they were part of the focus circuit (and they are, if I'm not
mistaken).

That's done to improve focus tracking (making focus less dependent on beam
current i.e. screen brightness).

Please forget my above remark. It's wrong.

Raymond

On Wed, Apr 7, 2021 at 01:25 AM, Dave Peterson wrote:

I thought they were part of the focus circuit (and they are, if I'm not
mistaken).

That's done to improve focus tracking (making focus less dependent on beam current i.e. screen brightness).

Raymond

On Wed, Apr 7, 2021 at 02:33 AM, Dave Peterson wrote:

But that's assuming the above links actual go to the pictures added. The forum
system is definitely weird: the new added pictures are not in any kind of
order relative to the existing album pictures. So just hoping for the best
here.

The links are fine. I just wouldn't add the quotes because they are of no help, at least not to me, neither in Firefox nor in Chrome. Either highlight the whole url, including the trailing digits, and open in a new tab (right click) or have groups.io send messages as mail as well. In messages, you may just click the links; they are complete, at least in Thunderbird.

Raymond

On Wed, Apr 7, 2021 at 01:25 AM, Dave Peterson wrote:

I can't even hazard a guess as to the meaning of the wire color. I won't be
the slightest bit surprised to learn that there is meaning to the wire
coloring. Consider it an aspect of Tek design that I haven't contemplated yet.

Hi Dave,
Spoiler alert! Don't look any further if you want to think about it a bit more, but

here's the giveaway:

Brown and red stripes for the wire connected to pin 12 of the CRT, etc. Strictly following standard color code. Pin numbers below 10 have just one stripe on a white background.

Raymond

Uploaded a couple of new pictures, though I see that the one Raymond uploaded does also show VR1434/C1434. Just didn't realize yesterday those were the pin 12 drivers.

This one shows the same diagram with the two components highlighted: "/g/TekScopes/photo/262670/3203258?p=Name,,,20,0,0,0"

This one is a close up without the annotations that should make them more visible: "/g/TekScopes/photo/262670/3203259?p=Name,,,20,0,0,0"

But that's assuming the above links actual go to the pictures added. The forum system is definitely weird: the new added pictures are not in any kind of order relative to the existing album pictures. So just hoping for the best here.

Dave

Thank you, Raymond and Siggi, for taking the time to answer to this post. Unfortunately the motor of the blower is beyond repair (back side bushing is completely broken), therefore the whole stuff must be replaced. I've seen a blower that might be appropriate for the purpose, beside the obvious (and, as Siggi said, undesired) regular fan. I'm quite aware of all the issues (I recently put a fan on a 2235 and, yes, I had to go from 8V to 5V - for a 12V motor - to get a decent noise. For fan I was considering making some additional holes in the back cover to allow for easier flow; but no decision yet.
TT

Just to clarify, because it seems I might have mislead Stephen to think I was suggesting something needed to be done:

I was mystified as to how the "mesh" was being driven at all because I missed that the tube schematic in the early service manual only has a pin 12 indicated in a different location than on the later service manual schematic. AND the later tube schematics include a dashed line indicating the mesh/grid in the tube.

So I completely missed that pin 12 was driven by VR1434 and C1434. I thought they were part of the focus circuit (and they are, if I'm not mistaken). So Stephens early A9 board does drive pin 12, just differently. I learned something. Stephen, I will try to remember to post a picture in your album showing the location of VR1434 and C1434 from the early service manual. Then you'll see where they are on your board.

And no Raymond, I can't even hazard a guess as to the meaning of the wire color. I won't be the slightest bit surprised to learn that there is meaning to the wire coloring. Consider it an aspect of Tek design that I haven't contemplated yet. I will say that it has just entered my mental universe in another venue: power supply wiring to the vertical pre-amp board. I'm working on building a bench harness and have documented the color coding of the wires. Perhaps color is related to voltage? I see that the 'cal' lights are powered by 120v, and they are striped with one red and one brown. I think the source is a red stripe, and the switched wire is brown striped? Or is that the return/ground line with the brown stripe? I haven't recorded everything well enough yet to find the pattern. But now that you bring it up I know that I will be looking for it!

Dave

On Tue, Apr 6, 2021 at 11:31 AM, Raymond Domp Frank wrote:

IOW: If the image is fine without a bias, there probably isn't an expansion
mesh in your CRT...

Raymond

I don’t know that yet... But I’ll report back when I’ll get to it.
I’m working on another restauration project at the moment.

On Tue, Apr 6, 2021 at 11:34 AM, Raymond Domp Frank wrote:

Not sure if you were joking.

Raymond

Of course I was! ?

Raymond,

Yes, I read that. But I thought maybe it could eventually be modified. Which I was not gonna even try to do, even if it was possible.
I’ll just try to make it work the way it is.
After all, it was a parts scope to begin with.

On Wed, Apr 7, 2021 at 12:27 AM, Stephen wrote:

Because the designer was colorblind??

Not sure if you were joking. I was dead serious and Tek assumed people working on the 'scope weren't color blind. Have a look at the colors on the other wires going to the CRT.

Raymond

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

Thank you Michael! ?

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?? ??♂?

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.



Hope this helps.

--
Michael Lynch
Dardanelle, AR

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

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 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...

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