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I have a 2465 with a very similar sounding focus problem. In X-Y mode I cannot get completely down to a point only a short horizontal line (using astig & focus controls and focus if fully ccw so output of 0V from control pot) and I'm sure I shouldn't be working at the end of travel of the focus. I cannot also get a short vertical line!

The focus output is producing between -108 and -180V and supply rails look good (have replaced a few caps).

There is a not very obvious DC restorer circuit in the grid side which had a very slowly rising voltage out of an LF353 which does appear to work as per the diagram in the manual, but part of me wonders if this could be a bad CRT since

Sean, I don't know about the other diodes discussed earlier, but I have seen
those tiny glob ones with the dot (in the picture) before, in Tek and other
gear. They could be just a different version (stripline) package for regular
TDs, or they could be "back-diodes," which are a close relative. As I recall,
back-diodes are even more heavily doped than regular TDs, so they are already
in forward bias at zero volts, and the interesting part of their behavior
exists around the zero-crossing, and includes that small region that seems
kind of like a crappy TD. Your mention of the weird curve reminded me. So,
don't assume they're bad TDs just yet, until you study it some more. Somewhere
in the circuit description or schematics it may become more clear. I don't
recall what the usual TD part designations are, but somewhere in tekwiki,
there's a nice listing and summary of many TD numbers from the old days. Look
for that - it may explain what TD253 is supposed to be. Also, you can look up
back-diodes, and see if the description matches the curve you saw.

You are right that this unit is a prototype. If the same phase development
stages were used back then, as in more modern times, then "B11" should be very
close to what went into production. The poor solder joints you mentioned,
around those tiny diodes, may result from a couple of considerations. First,
those things are very delicate, so anyone soldering them in or out would know
they have to work fast - very fast - to get that iron tip out of there ASAP,
even if the joint looks crappy, as long as it worked. Second, being a
prototype, these diodes may have been swapped out or had type changes many
times during development, and the same soldering issues apply. This could also
mean that those diodes are not necessarily the same part number that was
ultimately used in production. But, you'd think they would be close at least.
Good luck in figuring it out.

Ed

On Feb 27, 2021, at 20:29, Chappy <sb.chadwick@...> wrote:

"Ummm...for experimentation purposes one could probably wrap the probe and cable with some grounded aluminum foil."

I tried this last week. It had no effect.

On Feb 27, 2021, at 20:29, Dave Daniel <kc0wjn@...> wrote:

Think, Chuck, think.

On Feb 27, 2021, at 19:13, Chuck Harris <cfharris@...> wrote:

Does putting a tinfoil hat on your head take care of
the need for a screen room? Asking for a friend...

-Chuck Harris

Dave Daniel wrote:

Ummm...for experimentation purposes one could probably wrap the probe and cable with some grounded aluminum foil.

DaveD

On Feb 27, 2021, at 18:15, Jim Ford <james.ford@...> wrote:

And if/when that becomes a problem, you're going to need a screen room.
Not cheap, although I suppose if you have small enough devices under test, you could build a small screened chamber. Haven't tried it myself, but it does sound like an interesting exercise.

Jim Ford

------ Original Message ------
From: "Ed Breya via groups.io" <edbreya@...>
To: [email protected]
Sent: 2/27/2021 2:10:10 PM
Subject: Re: [TekScopes] P6021 Noise Problem?

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed

On Feb 27, 2021, at 19:13, Chuck Harris <cfharris@...> wrote:

Does putting a tinfoil hat on your head take care of
the need for a screen room? Asking for a friend...

-Chuck Harris

Dave Daniel wrote:

Ummm...for experimentation purposes one could probably wrap the probe and cable with some grounded aluminum foil.

DaveD

On Feb 27, 2021, at 18:15, Jim Ford <james.ford@...> wrote:

And if/when that becomes a problem, you're going to need a screen room.
Not cheap, although I suppose if you have small enough devices under test, you could build a small screened chamber. Haven't tried it myself, but it does sound like an interesting exercise.

Jim Ford

------ Original Message ------
From: "Ed Breya via groups.io" <edbreya@...>
To: [email protected]
Sent: 2/27/2021 2:10:10 PM
Subject: Re: [TekScopes] P6021 Noise Problem?

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed

You will still have to let it boil for long enough to displace
all of the air. May as well let it boil from the start.

-Chuck Harris

Does putting a tinfoil hat on your head take care of
the need for a screen room? Asking for a friend...

-Chuck Harris

Dave Daniel wrote:

Ummm...for experimentation purposes one could probably wrap the probe and cable with some grounded aluminum foil.

DaveD

On Feb 27, 2021, at 18:15, Jim Ford <james.ford@...> wrote:

And if/when that becomes a problem, you're going to need a screen room.
Not cheap, although I suppose if you have small enough devices under test, you could build a small screened chamber. Haven't tried it myself, but it does sound like an interesting exercise.

Jim Ford

------ Original Message ------
From: "Ed Breya via groups.io" <edbreya@...>
To: [email protected]
Sent: 2/27/2021 2:10:10 PM
Subject: Re: [TekScopes] P6021 Noise Problem?

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed

I have a 2465 with a very similar sounding focus problem. In X-Y mode I cannot get completely down to a point only a short horizontal line (using astig & focus controls and focus if fully ccw so output of 0V from control pot) and I'm sure I shouldn't be working at the end of travel of the focus. I cannot also get a short vertical line!

The focus output is producing between -108 and -180V and supply rails look good (have replaced a few caps).

There is a not very obvious DC restorer circuit in the grid side which had a very slowly rising voltage out of an LF353 which does appear to work as per the diagram in the manual, but part of me wonders if this could be a bad CRT since

Ummm...for experimentation purposes one could probably wrap the probe and cable with some grounded aluminum foil.

DaveD

On Feb 27, 2021, at 18:15, Jim Ford <james.ford@...> wrote:

And if/when that becomes a problem, you're going to need a screen room.
Not cheap, although I suppose if you have small enough devices under test, you could build a small screened chamber. Haven't tried it myself, but it does sound like an interesting exercise.

Jim Ford

------ Original Message ------
From: "Ed Breya via groups.io" <edbreya@...>
To: [email protected]
Sent: 2/27/2021 2:10:10 PM
Subject: Re: [TekScopes] P6021 Noise Problem?

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed

Chuck, do you mean SF6?LarrySent via the Samsung Galaxy S10
-------- Original message --------From: Chuck Harris <cfharris@...> Date: 2/27/21 3:04 PM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] WTB: Tek 576 and P6015A That is surprising, given that it is fully liquid atfreezer temperatures and atmospheric pressure.I just pulled mine from the freezer and checked them,and they are still full.Another option is HF6.? Freeze it, put some liquid inthe probe, when it all has boiled off, seal the probe.-Chuck HarrisPaul Amaranth wrote:>> -----Mensaje original-----> I had a small, sealed bottle for my probe stored in my freezer.? When I went to fill the> probe, it had all evaporated leaving me with an empty, sealed, bottle.> > This had been repackaged by a list member some years ago when he had acquired a small> amount.> > Butane sounds like a good alternative to me.? From what I can see from a limited search, it> cuts the voltage rating in half compared to R114.? At least the probe is usable at that point.> >?? Paul>

On Feb 27, 2021, at 18:15, Jim Ford <james.ford@...> wrote:

And if/when that becomes a problem, you're going to need a screen room.
Not cheap, although I suppose if you have small enough devices under test, you could build a small screened chamber. Haven't tried it myself, but it does sound like an interesting exercise.

Jim Ford

------ Original Message ------
From: "Ed Breya via groups.io" <edbreya@...>
To: [email protected]
Sent: 2/27/2021 2:10:10 PM
Subject: Re: [TekScopes] P6021 Noise Problem?

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed

On Feb 27, 2021, at 17:37, Chuck Harris <cfharris@...> wrote:

That is surprising, given that it is fully liquid at
freezer temperatures and atmospheric pressure.

I just pulled mine from the freezer and checked them,
and they are still full.

Another option is HF6. Freeze it, put some liquid in
the probe, when it all has boiled off, seal the probe.

-Chuck Harris

Paul Amaranth wrote:

-----Mensaje original-----

I had a small, sealed bottle for my probe stored in my freezer. When I went to fill the
probe, it had all evaporated leaving me with an empty, sealed, bottle.

This had been repackaged by a list member some years ago when he had acquired a small
amount.

Butane sounds like a good alternative to me. From what I can see from a limited search, it
cuts the voltage rating in half compared to R114. At least the probe is usable at that point.

Paul

Jim:
See the e-mail I just nest you off-list.

Liam @ PEARL, Inc.

Let me see, I meant. Cursed auto-spell! Jim

I hope the guy who invented spellcheck is burning in hello

If you have an RF spectrum analyzer, or access to one, you can easily see what's out there, and identify the exact frequencies and likely sources. We're awash with all sorts of EMI from everything in the environment, so assume there will always be some fuzziness added to measurements at higher sensitivities - it's just part of the deal.

Ed