[Hitokiri]

Hey

Can someone show me what and where the so called shield of a vacuum tube is?

There is always this debate about grey and silver shields. I would like to check if my tube has grey or silver shields but i don't know what i should look at. Tube in question is a Siemens E88CC.

Tyty

 

[tomb]

You really don't have a "shield" in the E88C (6922/6DJ8), at least - not one you can connect to a circuit.

I suspect you are really asking about the getter flash, which is a silvery patch on the inside of the glass. It results from "firing" the getter at the point of sealing the tube under a vacuum.

This is a good link to study, if you are interested in the parts and operation of a vacuum tube: https://vacuumtubes.net/How_Vacuum_Tubes_Work.htm

This pic from that article may also help:

Unfortunately, the one thing it doesn't point out is the getter flash on the inside of the glass.

 

[Hitokiri]

I am not sure if the correct technical term is shield, but that's what everyone calls it (whatever it is). There is often the argument that Siemens E88CCa with grey "shield" are older and better sounding than the newer ones with silver "shield". I know it covers the anode.
Maybe it's this one but i am not sure

 

[tomb]

Please try to communicate a bit better. If you are talking about the silvery glass finish on the top of the tube, that's the getter flash. Refer to my post above for details.

If you're talking about the green rectangle, that's merely a structural support in the tube.

 

[tomb]

It may be that people define sound differences between tubes as having a distinguishing structure that's different from another tube of the same type. However, that distinguishing structure is usually something that has an effect on the sound. There would have to be other parts that were different as well, if that structural support is to what you're referring.

All that said, structural differences are often cited as differences, but I don't think it would apply if everything is the same, except one structural support is gray and another is silver, but otherwise totally identical.

 

[Hitokiri]

Well, i am trying my best, but english is not my native language.

No i am not referring to the getter flash.

For some reason Siemens, and maybe other tube manufacturers aswell, somewhere between 1960 and 1965 (don't know the exact year), started changing the color of this so called "shield".

Reportedly, the tubes prior to that change sound better, there are various theories why that is. Of course any sonic differences aren't due to the color of the "shield" itself But it's just used novadays to distinguish the different versions, they grey ones are rarer, more sought after and costlier.

Here is an example:
https://www.tubemuseum.org/ProductDetails.asp?ProductCode=SH_E88CC_1958 (grey shield)
https://www.tubemuseum.org/ProductDetails.asp?ProductCode=SH_CCa_59-QUAD (silver shield)

The technical term in german is "Anodenblech", which translates to "Anode-plate", probably a plate that protects the anode and thus the name shield.

But i am not sure, when looking at a tube where that thingy is. The only thing that is either grey or silver depending on the tube is that structural support you mentioned.

 

[Monsterzero]

Are you talking about the plates?

 

[Hitokiri]

Are you talking about the plates?

I looked it up and i've soon some list them as grey or silver plates. So yeah, prolly same thing.

 

[Monsterzero]

These are the plates.

 

[Hitokiri]

Then it can't be that, because the plates are grey in every tube. I'll just ask a seller, upscale audio or something.

 

[tomb]

Then it can't be that, because the plates are grey in every tube. I'll just ask a seller, upscale audio or something.

It depends on the tube. The most common color is probably gray, but there are a lot of black plates out there, too. Silver is not that common, I think, but I'm sure there are examples somewhere.