Meaning of red border/markings on old Tektronix analog scopes (images included)?

[SharpEars]

What does it mean if the 246* (e.g., 2465/2467) oscilloscope screen has a red border around it and red grid markings (silkscreen)? Is it a different (better?) type of screen than the normal black border/markings oscilloscope screen? Or is this just a cosmetic thing?

I am talking about a screen like this:



Notice the red border and grid around/over the screen. It is found on some models but not on others. What does it mean?

Here is an example of the same model scope without the red border:

[TiN]

  That's just bulb backlight.

[SharpEars]

That's just bulb backlight.

So it's just the angle that the picture is taken at? When it's from the front it shows a red background and when it's from the top, it's black?

[Howardlong]

That's just bulb backlight.

So it's just the angle that the picture is taken at? When it's from the front it shows a red background and when it's from the top, it's black?

Not really, it's just the graticule illumination which is adjustable from the front panel. In normal use I leave it off all the time. If it's on an ad or auction it's showing, "Look, the graticule still lights up".

[edavid]

It's not just the graticule illumination... there were 2 different types of display filters that were used: clear and blue.  Hard to say which one is better.

[SharpEars]

That's just bulb backlight.

So it's just the angle that the picture is taken at? When it's from the front it shows a red background and when it's from the top, it's black?

Not really, it's just the graticule illumination which is adjustable from the front panel. In normal use I leave it off all the time. If it's on an ad or auction it's showing, "Look, the graticule still lights up".

I see, thanks for the info! I thought it was some cool improved screen, but it's just a red backlight ...

[H.O]

At least my 2465B looks like the "red one" if I remove the blue sheet of plastic in front of the CRT....so I don't think there was two different models, it's just that the "red one" has lost its blue perspex/acrylic sheet.

EDIT: I took two random EBAY ads, one "blue" and one "red" and put them side by side. You can clearly see that on the "red" one there's something missing in front of the CRT, namely the blue plastic sheet. See attached.

[miguelvp]

I like the red graticule on my tek 7613  better:



than the one on my tek 7603:

[MarkL]

I see, thanks for the info! I thought it was some cool improved screen, but it's just a red backlight ...

Well, not exactly.  Both the graticule markings and the red border are on the inside of the CRT glass.  See photo.

The backlight bulbs are aimed into the bottom of the thick front glass and the light bounces off the red markings.

Many Tek scopes have a blue plastic filter placed over the CRT, and on many (all?) models the filter is removable.  On a lot of used scopes the blue filter has been removed and lost, so what you're seeing in your first picture is likely the bare tube.

As edavid points out, there's also a clear filter available but I don't see those very often because they're not as good for beam contrast.

[SharpEars]

...

Many Tek scopes have a blue plastic filter placed over the CRT, and on many (all?) models the filter is removable.  On a lot of used scopes the blue filter has been removed and lost, so what you're seeing in your first picture is likely the bare tube.

As edavid points out, there's also a clear filter available but I don't see those very often because they're not as good for beam contrast.

What is the purpose of the blue filter? Does it just protect the CRT or does it actually make the display more clear? In other words, does the monitor look more readable with or without it?

[klunkerbus]

Part of this ties back to the days before digital data.  Any decent lab with scopes had polaroid-type cameras that would slip onto the CRT for capturing a photograph image of the screen.  I don't remember adding/removing filters, but I can imagine that they'd make a difference in how various film would capture the signal and graticule.

EDIT: Now you also better understand the reason for the raised rim around the CRT. It served as the camera mount.

[miguelvp]

That's also why those three connectors where there on the left of the screen, to provide power to the camera.

[edavid]

What is the purpose of the blue filter? Does it just protect the CRT or does it actually make the display more clear? In other words, does the monitor look more readable with or without it?

That's controversial... many users think it improves display contrast under room lighting, but ex-Tek engineer Steve Ditter has claimed on the TekScopes list that it was just cosmetic.

[SoundTech-LG]

If anyone has blue filters they want to sell for the 2467B, let's hear it!  Hard to find!

[AF6LJ]

What is the purpose of the blue filter? Does it just protect the CRT or does it actually make the display more clear? In other words, does the monitor look more readable with or without it?

That's controversial... many users think it improves display contrast under room lighting, but ex-Tek engineer Steve Ditter has claimed on the TekScopes list that it was just cosmetic.

I have never seen a difference, They did make green filters, a friend's Tek 475 has one.
To me looking at faint traces both filters are an impediment.
I ditched the blue filter on my Tek 466, for that reason and because it was scratched all to hell.

[Electro Fan]

Part of this ties back to the days before digital data.  Any decent lab with scopes had polaroid-type cameras that would slip onto the CRT for capturing a photograph image of the screen.

+1 (It facilitated photographing the display)

[edavid]

Part of this ties back to the days before digital data.  Any decent lab with scopes had polaroid-type cameras that would slip onto the CRT for capturing a photograph image of the screen.

+1 (It facilitated photographing the display)

I don't get it, how would the blue filter make any difference?

[Electro Fan]

Part of this ties back to the days before digital data.  Any decent lab with scopes had polaroid-type cameras that would slip onto the CRT for capturing a photograph image of the screen.

+1 (It facilitated photographing the display)

I don't get it, how would the blue filter make any difference?

I don't know about the filter color but I think the theory is that the red illumination provides contrast that helped capture a good image with film photography.  When you see a scope with a blue filter and no red it's generally because the scale  illumination ("scale illum") knob was turned all the way down/off; if it is turned on/up the red lines will appear (if the red scale illumination is working properly).

[Macbeth]

If anyone has blue filters they want to sell for the 2467B, let's hear it!  Hard to find!

Just get a piece of coloured plastic film.

This reminds me of the old "colour TV upgrade" scam for B&W tellies in the 70's. I think you ordered by screen size and got a coloured film that attached to the front of the tube. It had green on the bottom (for the land), blue on the top (for the sky), and god knows in the middle. 

...I just had to google because I thought maybe I was dreaming it, but yes it was a real thing!

[SaabFAN]

If anyone has blue filters they want to sell for the 2467B, let's hear it!  Hard to find!

I would suggest color filter-foils for Stage-Lights. They are only a few € for 100x50cm pieces.

[helius]

The color filters are based on the properties of the CRT phosphor, not the camera.
Phosphors were used with multiple emission wavelengths, but the time constant of the different colors was not the same. With no filter, the longer time constant (in green or yellow) would make the trace easier to see at slower timebases. When photographing with Polascope 10000 only the blue light with the fastest decay was needed, the other colors would smear the image.

[fivefish]

In photography, it was blue filter when using daylight film in a tungsten-lighted environment.  But don't know if that's related to the blue filter in a scope.

[BravoV]

I believe the red back light is designed to make the graticule stands out to improve reading, especially in dark surrounding ambient light.

Few shots from my 2465B, an example with the red back light turned off :




Red back light on :

[fivefish]

or when printed in black/white publications... back in the 80s.

[edavid]

If anyone has blue filters they want to sell for the 2467B, let's hear it!  Hard to find!

I would suggest color filter-foils for Stage-Lights. They are only a few € for 100x50cm pieces.

They are too thin and floppy, so they don't fit in the holder.  0.03" thick plastic sheet is good, but hard to find.

The color filters are based on the properties of the CRT phosphor, not the camera.
Phosphors were used with multiple emission wavelengths, but the time constant of the different colors was not the same. With no filter, the longer time constant (in green or yellow) would make the trace easier to see at slower timebases. When photographing with Polascope 10000 only the blue light with the fastest decay was needed, the other colors would smear the image.

Not an issue with the standard P31 phosphor used in most Tek CRTs.

[Rupunzell]

The red internal graticule was done as contrast enhancement and increasing graticule visibility with black & white film as red tends to appear darker(than CRT beam) with black & white film's rendition of tone-contrast for a given light spectra. The front filters appeared in Blue (most common), Dark neutral density (lesser common) and the fine mesh RFI-EMI shielding specifically designed to reduce emissions form the CRT.

Color filters can be placed between the incandescent graticule lamp to plastic light pipe to alter the graticule color, it is not often done, but can be done.

My fave is to use a sheet of polarizing film cut to fit the plastic filter holder behind the Tek's plastic CRT front. This adds nice contrast enhancement to the display in high ambient light conditions. This is why the O'scope images posted here appear the way they do.

Blue is most common due to the light spectra of the CRT's phosphor, the most common being P31. In the past there were other phosphors offered by Tek and others specifically designed to increase photographic film writing speed trading human eye visibility. Other phosphors offered by Tek had longer or shorter persistence and other specific features for a given phosphor type.


Bernice