Amperex 6DJ8 tube construction


Here is a link to a picture of two Amperex 6DJ8 orange globes.
- The one on the left has a circular plate suspended between the grid and the O getter.
- The one on the right does not have the circular plate suspended between.

What does that circular plate do? Why is it not necessary in the other tube? Any other info?  Thx!



steakster
i am not knowledgeable on the fine points of how specific vacuum tubes are constructed, perhaps there or others that can comment who have more knowledge

i would say, having a fairly vast connection of such tubes of various brands/makes from us europe japan etc, 6dj8, 12au7, 12ax7, 6fq7 and so on, that both types of construction you show via the link are quite common... i see more of the ones with the ’intermediate horizontal plate’ leading up to the suspended getter on somewhat later iterations of the various tubes, perhaps it is to make the tube more robust against mechanical shocks and not go microphonic or worse
Left one is Amperex Holland made and a great tube, the one on the right is a Matsushita made on same tooling as Mullard but a different tube.
Always check the etched codes at bottom of tube to identify the origin.
'Made in Holland' is silkscreened on the one on the right. It matches several other ’Made in Holland’ silkscreens on NIB/NOS Amperex 6DJ8 orange globes that I purchased in the original yellow/green boxes, years ago. There are no date/factory etchings on these tubes in the original yellow/green boxes. There are etchings on tubes, similar to the one on the left.
I agree the one with the extra plate may be a ruggedized tube.
Does the left tube have the same Amperex logo? This is a guess, maybe the tube on the right was made in a Mullard plant and branded Amperex Holland. That happened sometimes.



I think the circular plate is called a splatter shield. I don’t know what its function is.

Tubes from the Phillips factories (Amperex, Mullard, Siemens, La Radiotechnique, Valvo, etc.) made in one factory often carried the label of another Phillips factory. I have lots of examples of this.

The only way to be sure where and when a Phillips tube was made is to read the etched code. Sometimes part or all of the code is unreadable. I can see the delta etching on the tube on the left, which means it was made in the Heerlen Amperex factory. You would have to talk to someone a lot more familiar with tube construction than me to find out where the tube on the right was made.

Here is a link to the Phillips codes if anyone doesn’t have them:

https://frank.pocnet.net/other/Philips/PhilipsCodeListAB.pdf

The tubes we’re discussing and any we’re likely to come across would have the ’NEW’ CODE etchings.
The one on the left is Holland.

The one on the right looks to be Blackburn, England or Japanese.

If Blackburn it will have etched codes on the glass.

Japanese "Mullard" 6922 types usually have a slanted getter flashing that is higher/lower on opposite sides of the tube, but not always.

This "slant' was also common with some Eastern Euro 12 volt tubes from the 70's and maybe later on.

Anyway, both are desirable tubes if they test up to snuff.

DeKay
Everybody - thanks for the info. Solving a mystery is always fun.

With jeweler’s magnifying glasses, I wasn’t able find any codes - on any of the NIB/NOS Amperex 6DJ8’s in the yellow/green boxes. I looked everywhere - including the bottom and sides of the tubes. It was easy to find the the codes on the Heerlen-made tubes - of which I have several. The Heerlen-made tubes lasted several thousand hours in my preamp. Some are finally wearing out.

I’d like to find out more about the mid-circular plate. Unfortunately, no luck with a google search, re: vacuum tube splatter shield.

Maybe try Googling vacuum tube mica. Or mica types.

steakster, I found a couple of references to splatter shields, first from Joe’s Tube Lore:

"The next structure up is the unique one it’s a horizontal, circular, metal disc supported by two metal bars. I’ve seen & heard this referred to as a shield or a splatter shield. Which name is correct & what is the purpose of this structure? I don’t know, but most all early 6DJ8 family tubes have it."

https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#6DJ8

and this out-of-stock tube on Tubemonger’s site:

"LORENZ Stuttgart PCC88 7DJ8 SINGLE TUBES Gray Shield 1960s MINT NOS OEM NO LABEL - Getter Ring Fused with Splatter Shield Construction - Made in Germany"

https://www.tubemonger.com/LORENZ_Stuttgart_PCC88_7DJ8_Gray_Shield_Germany_II_p/1054b.htm

I think you’ll have to call a tube dealer to get an answer. Let us know if you get one.
Joe's Tube Lore refers to the A frame type but that tube by construction does not have the ususal type of shield as earlier tubes (like the one on left picture).
What is common in Dutch made tubes, including Mullard, Amperex USA, French, Belgian, Indian and so on, and German tubes like Siemens and Halske, Telefunken (same tooling and construction for early Teslas also) is the ridged shield - a plate with two ridges 180 deg apart.
Sylvania, Tungsram (Hungary) had a plate shield with no ridges.
All for ecc88 family of tubes.

Joe’s Tube Lore refers to the A frame type but that tube by construction does not have the ususal type of shield as earlier tubes (like the one on left picture).

No, Joe is describing the tube on the left in the picture in the section I quoted. The A frame tube has a getter (not a splatter shield) supported by 2 angled, wide metal supports.

http://tctubes.com/images/products/detail/435_ECC88_AMP_800.JPG

Richardson Electronics purchased the Amperex name years ago and rebadged/boxed tubes of various origins as Amperex.

The only ones I purchased were 6dj8's and 6922's that were of Japanese manufacture.

DeKay
After reading posts near the bottom of this discussion, it appears that it became the Wild West for NOS tubes in the 1990’s. Lots of re-branding and fakes going on.
This is just a guess, but a splatter shield may be to prevent secondary emissions.
Brent Jessee -from Audio Tubes - was kind enough to explain.

The splatter shield prevented getter flash material from migrating down during the flashing process. Without the shield the flash material could stain the grid and/or plates and affect the operation of the tube. The shield has no effect on the sound and like the o getter is pretty much useless after the getter flash process is complete.


I can add a bit to that. The getter is used to trap all remaining air molecules in the aluminum of the getter. After all the air is pumped out and the glass sealed, the getter is fired with a very high voltage. The air is thus trapped in an aluminum deposit seen on the inside of the glass near the getter. Because its aluminum, if the glass seal is lost, the getter deposit turns white with aluminum oxide in a matter of minutes.

The getter can be ’over-fired’. If this happens other elements in the tube can be contaminated. That splatter shield takes care of that (I wish they were used in Chinese tubes, which are often over-fired..). As Amperex improved their technique, the splatter shield wasn’t needed. Getting rid of it is a good thing, since it can contribute to microphonics.