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Dave,

Happy to be of service.

-- Jeff Dutky

Well,

I finally got me some 2N3442s from mouser.

Good news: the HV sparking problem was definitely cause by the 75V regulator going short.

Bad news: there appears to be no vertical deflection. But, there's a caveat to that. I'm pretty certain the problem lies downstream of the front end amplifiers because the channel 1 out signal is present and responds to vertical position control when viewed on another oscilloscope.

Another symptom is that the spot is about 1 cm long in the X dimension when the time base is slowed down. I'm hoping the 75V rail going high didn't take out a bunch of stuff!

Sean

Going to get this on the bench again this weekend and tinker with it. I couldn't get the shaft to come free; was afraid of breaking something. Will need to examine again.

Sean

That dang Jeff Dutky keeps making me spend money on test equipment!

LOL.

Last I'd checked there wasn't any availability. R&L has them now! Get 'em while their hot!
Dave

Jonathan Pyle wrote:

I don't have a function generator that can produce frequencies in the hundreds of MHz,
and I don't have a spectrum analyzer that can test the frequency response of the RF probe.

Good News! You can remedy both deficits by the acquisition of a TinaSA:

The TinySA is a spectrum analyzer that can operate on signals between 100 KHz and 960 MHz (in two ranges), it can generate sine waves up to 350 MHz, and square waves up to 960 MHz, and it fits in the palm of your hand.

Make sure you buy from one of the reliable sources:

When I bought mine, earlier this year, I paid less than $60. I bought through the Zeenko store on AliExpress. It did take more than a month or the item to arrive, as I did not pay or expedited shipping.

-- Jeff Dutky

Charles --

I tested the RF probe from Ukraine that I got on eBay ().

I tested it with my 1S1 and my Leo Bodnar 30 picosecond pulse generator (10 MHz) and found that the measured risetime through the RF probe was around 300 picoseconds, which is the same as when the pulse generator is plugged directly into the 1S1.

However, the RF probe did add a lot of "ringing" to the waveform. See the photo in this album:

/g/TekScopes/album?id=262713

I'm not sure this is a fair test, though, because a 30 picosecond risetime contains frequencies well beyond the stated bandwidth of the probe (1.5 GHz), so maybe that messes things up?

The RF probe comes with a nice telescoping needle probe point, but I desoldered it because I thought it might introduce noise. Removing it did not have any noticeable effect. I soldered an SMA socket to the RF probe input for purposes of attaching the pulse generator without any long leads. (The pulse generator wants 50 ohms so I used a T and a 50 ohm terminator.)

I did another test with a 10MHz signal from my Koolertron function generator (low cost Amazon product) through a 3-foot BNC cable (well within the bandwidth of the probe). The waveform looks the same through the RF probe, just noisier.

I don't have a function generator that can produce frequencies in the hundreds of MHz, and I don't have a spectrum analyzer that can test the frequency response of the RF probe (see the eevblog post above).

For $21.20 including shipping I think it's a pretty handy device. (Shipping to the U.S. took only eight days.)

Also consider that some of us are pretty good at 3D printing blowers
that will fit onto a case fan hub ;-)

Monty
(the other one)

On Tue, Apr 6, 2021 at 9:03 PM cheater cheater
<cheater00social@...> wrote:

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

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