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Products => Test Equipment => Topic started by: BlownUpCapacitor on December 28, 2023, 09:01:00 pm

Title: Hexagonal Dots in an Unfocused CRT Beam on Tek 2230
Post by: BlownUpCapacitor on December 28, 2023, 09:01:00 pm
Hey y'all! I've had this Tek 2230 for quite some time, and it's a wonderful scope. It has no issues and works perfectly.

However, every time I unfocus the beam I notice tiny dots in the beam, as if there was a tiny honeycomb chain link fence in the CRT, like a shadow mask.

This isn't a problem at all, but it has always made me ponder what it could be.

Maybe someone who worked at Tek here knows the true answer.

I've had people guess it was a Shadow Mask or Aperture Grill of a CRT, but this is a monochrome CRT so it shouldn't have one. Others have thought it was the collector mesh, but those are used in analog storage CRTs. This is just a regular oscilloscope CRT.

Anyways thanks for taking a look here! I've provided some images below.
Title: Re: Hexagonal Dots in an Unfocused CRT Beam on Tek 2230
Post by: BrokenYugo on December 28, 2023, 09:07:46 pm
Regular higher speed scope CRTs use post acceleration, several kV above the deflection plates. I think that's what it's for, probably a linearity thing using a mesh.
Title: Re: Hexagonal Dots in an Unfocused CRT Beam on Tek 2230
Post by: BlownUpCapacitor on December 28, 2023, 09:18:52 pm
Quote from: BrokenYugo on December 28, 2023, 09:07:46 pm
Regular higher speed scope CRTs use post acceleration, several kV above the deflection plates. I think that's what it's for, probably a linearity thing using a mesh.

I don't think the CRT in the 2230 has such a mesh though.

I know a scope like the 465B utilizes the mesh, and that mesh shows up in the schematics. (images provided below)

However, the CRT circuit schematic of the 2230 does not show such an acceleration mesh.
Title: Re: Hexagonal Dots in an Unfocused CRT Beam on Tek 2230
Post by: colorburst on December 28, 2023, 09:44:07 pm
Quote from: BlownUpCapacitor on December 28, 2023, 09:18:52 pm
I don't think the CRT in the 2230 has such a mesh though.

I know a scope like the 465B utilizes the mesh, and that mesh shows up in the schematics. (images provided below)

However, the CRT circuit schematic of the 2230 does not show such an acceleration mesh.

AFAIK they all had a scan expansion mesh by that point; this one just doesn't have it drawn on the schematic. The same CRT 154-0861-00 is also used in the 2213A, where it does show the mesh: https://w140.com/tekwiki/images/e/e5/070-4733-00.pdf (page 163 in the pdf).
Title: Re: Hexagonal Dots in an Unfocused CRT Beam on Tek 2230
Post by: BrokenYugo on December 29, 2023, 12:19:05 am
This sounds like the relevant patent.

https://patents.google.com/patent/EP0277758B1