vintage tube manufacturer identifying

[gary sanders]

Say you've got some old tubes with all the printing rubbed off.what are some distinctive things that help say who made it? like RCA,Mullard,etc....Or is there any at all?

[David Root]

Here's one for Philips family tubes (most of them), and RCA too. There is a little around that I've seen for GE, and nothing that I've seen for Sylvania.

There is also a better Euro tubes one at www.audiotubes.com and also a Telefunken guide too. Most Euro tubes, including Mullards, were etched with the mfr/date code, so they are easier to ID than US tubes, which were not etched like that. For example, a tube with etched code B8C4 was made by Mullard at the Blackburn (B) factory in the UK, in 1968 (8), in March (C) and the 4th week of March (4). Doesn't matter what the paint on the tube says, the etched code is it.

There is more to it than that though. Some of these codes can be ambiguous (not many). For example, a 12AX7 with a 17mm long plate structure is not later than 1960. Short plates (14mm long) can be late '50s thru mid '70s or so.

Any tube with no paint left on and no etched mfr/date code, is likely a US made tube. After about '52 or so, all GE tubes were etched with a characteristic pattern, and any tube with its number in an etched octagon was made by RCA. Other than that you you have to get to know what each manufacturer's tubes look like inside. Shape, location and size of getter(s) and flashing also helps.

Finer points include number of mica support discs (double, triple etc.), arrangement of the plate structure, which is the only part of the tube you can actually see.

[Phil_S]

You might try the freezer trick. Seriously. Put the tube in the freezer for a while. You have a very brief moment when you remove the cold tube, when there is some condensation on the glass. Sometimes that will reveal markings that used to be there.

[David Root]

Ingenious! Never thought of that.

[yowza]

Telefunken have the tell tale diamond shape on the bottom of the tube imprinted in the glass in the middle of the tube pins.
I recently found some old tubes that were labelled Fisher electronics made in West Germany that had the diamond shape on the bottom which indicates they were made by Telefunken for Fisher.

I too have a bunch of old tubes that are lowly losing their labels. Is it ok to write something on the tube with a marker to indicate brand before the labels fade or is this not good for the tube?

[David Root]

Lots of people do that. Personally I wouldn't. I put a small marker spot on top of the tube top, and the same marker spot on its box, write the details on the box and you have it. EG "o", "+" "!" etc.

With most Euro tubes it's not necessary because the etching codes tell you (top line) what type the tube is, and (bottom line) factory, year of production.

[gary sanders]

Here's one for Philips family tubes (most of them), and RCA too. There is a little around that I've seen for GE, and nothing that I've seen for Sylvania.

There is also a better Euro tubes one at www.audiotubes.com and also a Telefunken guide too. Most Euro tubes, including Mullards, were etched with the mfr/date code, so they are easier to ID than US tubes, which were not etched like that. For example, a tube with etched code B8C4 was made by Mullard at the Blackburn (B) factory in the UK, in 1968 (8), in March (C) and the 4th week of March (4). Doesn't matter what the paint on the tube says, the etched code is it.

There is more to it than that though. Some of these codes can be ambiguous (not many). For example, a 12AX7 with a 17mm long plate structure is not later than 1960. Short plates (14mm long) can be late '50s thru mid '70s or so.

Any tube with no paint left on and no etched mfr/date code, is likely a US made tube. After about '52 or so, all GE tubes were etched with a characteristic pattern, and any tube with its number in an etched octagon was made by RCA. Other than that you you have to get to know what each manufacturer's tubes look like inside. Shape, location and size of getter(s) and flashing also helps.

Finer points include number of mica support discs (double, triple etc.), arrangement of the plate structure, which is the only part of the tube you can actually see.

Good Stuff,man!