Need help finding a replacement CRT for a Hitachi scope.

[gkmaia]

Got to replace my Hitachi's Vc6025. CRT is a Toshiba E8365B31.

Ive found several documentation on these tubes but nothing really specific on my model.

https://tubedata.tubes.se/other/Toshiba/index.html

By looking at the documentation B31 stands for oscilloscope use, so it will have the matrix printed. That narrows it a bit. But apart from that I cannot find anything else. No mention to E8365.

On ebay I have seen several B31's. bit without knowing the specs I can't tell for sure if they interchange.

Anyone out there with some good knowledge on these tube that could give me a hand finding a replacement?

[bob91343]

Does the manufacturer offer any help?

[james_s]

For a 30 year old scope? I doubt there's anyone still working there that even remembers it.

[bob91343]

You never know; it doesn't hurt to ask.

[gkmaia]

That is an interesting one. A couple years ago I got a collection of those old leader portables 100, 200 and 300. and could not find the manuals anywhere. I got in contact with Leader on the US and there was still someone around from that time and he had the manuals.

I will try that.

[akimpowerscr]

Service Manual:

https://elektrotanya.com/hitachi_vc-6025-6045-6525-6545_complete.pdf/download.html

[drussell]

By looking at the documentation B31 stands for oscilloscope use, so it will have the matrix printed. That narrows it a bit. But apart from that I cannot find anything else. No mention to E8365.

On ebay I have seen several B31's. bit without knowing the specs I can't tell for sure if they interchange.

The P31 suffix (in this case, apparently Hitachi uses B instead of the more common P) is simply the phosphor type.  P31 phosphor (WTDS type GH) was originally registered by Mullard in March of 1960.  The G indicates "Bluish-green, green or yellowish-green" and the H indicates "Hitachi" in the WTDS phosphor designations.  P31 is formulated from Zinc sulfide with copper.

Many tubes were made with multiple different phosphor options, for example, some tube might be available in both P1 (old-school, original bright green) and P4 (the standard for B&W television for many, many years,) etc.

The part you care about is the actual type number and for this tube, since it is a scope tube, it will only be available with scope-specific (higher speed, lower persistence) phosphors.  The Hitachi datasheet you linked to says they only ever made it in P31, but if you look at others on those lists, you will see that some are available in multiple different phosphors.

Unfortunately, due to the limited number of tubes produced for applications like scopes, you're only  likely to find one from another scope being parted out or something...  and unlike the very early days where many different scope tubes could be used with the same basic, simple circuits, more modern scopes had tubes that were very application-specific, so you won't be able to interchange very far from the exact original type.

Good luck, though! 

[drussell]

What is the problem with it, anyway? 

Is it just getting dim from years of prolonged use?

[gkmaia]

It is distorting the image.

I bought a degaussing tool and must arrive tomorrow.

But from what I am reading could also be physical damage to the MCP due to drop while it was on transport.

[james_s]

Whoa, that's a weird one, yeah, my money is on mechanical damage. An xray of the CRT would prove this one way or another if you can't see through the neck.

[gkmaia]

I ran the degaussing tool and no luck... still distorted.

[doktor pyta]

@gkmaia

1. What MCP are You takling? This CRT has no Microchannel Plate.
2. this may be 'trapped charge' issue. I will try to find a thread about it.

[akimpowerscr]

You are probably referring to the aluminum layer that covers the phosphor on the screen.

Indeed, modern CRTs have aluminizing layers which serve three functions:

- To avoid buildup of charges on the phosphor which tends to slow down the electrons and limits the brightness.

- It serves as a light scatter. When the beam strikes the phosphor with aluminized layer, the light emitted back into the tube is reflected back towards the viewer which increases the brightness.

- The aluminum layer acts as a heat sink for the phosphor and thus reduces the chances of the phosphor burning.

I have already had the case with a Tektronix CRT where this aluminum layer had a continuity fault.

The electron beam seems to refuse to go to this area because it is repelled by the negative charge that forms there.

But here it doesn't seem to be the same problem

[coromonadalix]

seems like the crt yoke as some damage, or moved / loosen up

Check for physical damage on it  or some retaining screews has loosen

[drussell]

It is distorting the image.

I bought a degaussing tool and must arrive tomorrow.

Yeah, that is a really weird one for an electrostatic CRT...

Degaussing probably won't help if it is actually being distorted by the CRT, there really isn't anything in there that can get magnetized, although you should check that the chassis itself isn't magnetized somehow.  Degaussing is really for demagnetizing the shadow mask on a color tube, there is nothing at the screen end to get magnetized in a monochrome scope CRT.

I would open the scope and see if there is a way you can run it with the CRT propped up away from the chassis and see if it changes.  A stray magnetic field down near that lower right corner might be pulling the beam over there.  Also check that there weren't any correction magnets on the CRT that fell off.  Speaking of correction magnets, you might be able to rig something up yourself with some of that weak, self-adhesive stuff used to make fridge magnets to bring it back into alignment by sticking little bits on the outside of the CRT envelope.

[drussell]

You are probably referring to the aluminum layer that covers the phosphor on the screen.

Indeed, modern CRTs have aluminizing layers which serve three functions:

- To avoid buildup of charges on the phosphor which tends to slow down the electrons and limits the brightness.

- It serves as a light scatter. When the beam strikes the phosphor with aluminized layer, the light emitted back into the tube is reflected back towards the viewer which increases the brightness.

- The aluminum layer acts as a heat sink for the phosphor and thus reduces the chances of the phosphor burning.

Those are all benefits, and are the ones applicable to scope tubes since they're electrostatically deflected rather than magnetic, but you missed what was originally the most important reason for aluminizing.  Elimination of the requirement for an ion trap on magnetically deflected CRTs.

Residual gas atoms within the tube cause ions (charged atoms) to be produced when struck by electrons, so negative ions originate at or near the cathode, follow the same path as electrons in an electrostatic field but are only slightly affected by magnetic fields.  Since ions are considerably larger and heavier than electrons and the ions are capable of causing damage to to the phosphor screen where they strike it.  Since the magnetic-deflection field has much less effect on ions than on electrons, the ions tend to impact the screen near the centre, forming a darkened area known as an ion spot.

In early television, most CRTs were electrostatically deflected but as larger screens came about and magnetic deflection became the norm, methods of trapping the ions were developed (like the bent-neck, slashed-field gun and offset gun) using an external magnet to pull the electrons back into a straight line towards the screen, but leave the ions shooting off towards the side of the neck or envelope.

The mass production of aluminized screens in the early '50s led to the elimination of the need for ion traps since the aluminum layer prevented the physically large ions from penetrating it while allowing the electrons through to the phosphor.  The added brightness from reflecting the light forwards instead of back into the tube was just an added bonus. 

[drussell]

seems like the crt yoke as some damage, or moved / loosen up

Check for physical damage on it  or some retaining screews has loosen

Dude, it's an oscilloscope.  It doesn't have a deflection yoke, it uses electrostatic deflection, not magnetic... 

[CaptDon]

Scopes don't use yolks!!!

[james_s]

You are probably referring to the aluminum layer that covers the phosphor on the screen.

Indeed, modern CRTs have aluminizing layers which serve three functions:

- To avoid buildup of charges on the phosphor which tends to slow down the electrons and limits the brightness.

- It serves as a light scatter. When the beam strikes the phosphor with aluminized layer, the light emitted back into the tube is reflected back towards the viewer which increases the brightness.

- The aluminum layer acts as a heat sink for the phosphor and thus reduces the chances of the phosphor burning.

I have already had the case with a Tektronix CRT where this aluminum layer had a continuity fault.

The electron beam seems to refuse to go to this area because it is repelled by the negative charge that forms there.

But here it doesn't seem to be the same problem

There is another purpose of the aluminum layer too, it stops ions from damaging the phosphor, the first aluminized tubes removed the need for the ion trap, where the gun was pointed at an angle and used a magnet to deflect the beam back toward the screen without deflecting the ions.

*Edit: Oops, drrussell beat me to it, and explained it in more depth. I should probably read the whole thread before I respond to something.

[CaptDon]

There are probably several plug-n-play crt's with the same pinout.
Check with Sphere electronics and his extensive knowledge and supply
of scope tubes and dead scopes stripped for parts. Keep checking Ebay.
I need either a 5abp7a or 5adp7a aluminized crt. can't seem to find
the 'A' version with the aluminized screen. The A version is about 30%
brighter for the same beam current!!

[gkmaia]

I have two of these VC6025. I did swap just the CRT, just it, not even the connector board. And the problem stays with the faulty CRT.

Definitively the CRT.

I did remove the aluminium cover and could not see any bent or physical damage to plates.

[bdunham7]

It is distorting the image.

I bought a degaussing tool and must arrive tomorrow.

But from what I am reading could also be physical damage to the MCP due to drop while it was on transport.

That looks like mechanical damage.  Try this:

In a very quite room, hold scope up in the air and roll it around.  If you hear any little bits moving around, you may have a broken bit of glass or something in the tube.  If so, stand it on its back and shake it a bit back and forth, then slowly roll it forward while continuing to shake it until it is 45 degrees nose down.  Then carefully set it down, plug it in and try again.

If that helps it is definitively broken inside.  If it doesn't, then it is still very likely broken inside.

[james_s]

If I were nearby I would offer to xray the CRT for you to see the inside, but it would not be economical to send it to me. Maybe you have a curious veterinarian around? Most animal clinics have xray machines and they are not mired in all of the rules and regulations that human clinics have to deal with.

[drussell]

Having a pretty thorough understanding of the construction of various types of CRTs throughout their history, I'm having real difficulty wrapping my head around what could possibly be wrong with this specific specimen to cause that particular kind of crazy output!

Maybe some sort of coupling between the vertical and horizontal plates somehow, but only when the voltage differential swings towards the lower part of the screen on the (whatever it is, positive or negative) one side??   

It's totally weird that it works fine at the top of the screen and is fine along the lefthand edge but bends only in that one part in the middle...  Bizarre!!

Somehow something like when you get a carbon track between terminals in a distributor cap and it starts to affect the nearby terminal?  It is so strange that it only affects that one area.

I really don't get it, that is probably the weirdest CRT issue I've ever seen, especially on an electrostatically-deflected CRT!  Usually those things are pretty much invincible unless you wear out the cathode or break it and let it go to air somehow...   

[jdragoset]

The "Aluminum" cover you refer to is very likely Mu metal, which is intended as a magnetic shield.
Many come with a printed warning label about bending or creasing causing magnetic problems.
This shield could be checked with a magnetic compass by standing the scope with the display straight up and hold the compass horizontal while passing it around the shield, one elevation at a time.
Any movement in needle position would indicate a magnetized area of the shield that could be degaussed.