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Question about coding on tube

maxseeley

Member
2010-03-27 7:58 pm
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I have a set of tubes (see pictures):

The coding on the side of the tube is
GA0 B6L3
&
78-26

My translation of this is:

Tube Type: Ecc88 (code GA - this is correct)

Change Code 0

Made in Mullard, Blackburn factory (code B - this part confuses me because on the tube it says "Made in USA"

6L3 - Made in the 3rd week of December 1956 or 1966 - my understanding is that they changes over to the new coding system in 1956.......

Also, what does the 78-26 signify (this is in larger type white paint and the above listed code is in the typical hard to read really small type)
 
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I don't think the ECC88 had been invented in 1956, so it will be 1966. Also, as you imply, earlier date codes used 3 characters only.

Country of manufacture was often a pack of lies, so I am not at all surprised to find USA on something made in Britain.

Having said all that, the Philips code on these looks unusual: it is too large, upside down and appears to be paint rather than acid etch. So could these be later production, with a dodgy 'etch code' to increase their value? Are there any codes in faint brown near the bottom, right way up?
 
I am not an expert on these matters, but the getter in your valves looks like the later dish pattern. This would be consistent with a 1978 date, I think. Are these really late GA2, remarked as early GA0? Probably still fine valves, but not quite what they claim to be?

Can you check them? If they have been remarked then these is a slight risk that they are really ECC189 - the remote cutoff version. OK for phono input, but not line stages or phase spiltters.
 

maxseeley

Member
2010-03-27 7:58 pm
I know the tubes are authentic - they came from my work and the person who bought them (RIP) got them 30 to 40 years ago in bulk for equipment. He was EXTREMELY detail orientated and I don't think there was a lot of fake stuff going around back then. Plus, he would have bought them directly from HP.
 

SY

diyAudio Moderator Emeritus
2002-10-24 10:19 pm
Chicagoland
www.SYclotron.com
Actually, it would have been just about 30 years ago that relabeled 6ES8 were being sold off in large quantities as ECC88. There's still plenty of those mislabeled tubes floating around; when I hear someone complain about the linearity of ECC88, I can be nearly certain that their experience is with one of those variable mu tubes.

Not that any of this matters- there are plenty of excellent ECC88 types available.
 
from my scant tube lore knowledge, HP tubes were pretty much "cream of the crop". But the 70s were a strange time for tubes - these could be sourced from Britain, but that crosshatch pattern on the top almost looks Japanese.

If you're still curious, I can forward these pics to a friend of mine who is uh, a little obsessed with this type of rare knowledge.
 
The glass seams on the top more or less guarantee that the valves were made using Philips tooling, but not necessarily in a Philips-group factory as in the latter days they shipped it out to other places such as Ei (Serbia) or BEL (India). The dimpled-dish getter was most popular in the Dutch Heerlen factory, but appeared elsewhere too.
 
my friend wrote:

The tube codes are especially visible on the tube on the right in picture number 2:

"GA" is the Philips internal factory code for the ECC88/6DJ8 type.

The factory code is "B" They are late 1970s Blackburn Mullards.

Probably made for a defense contract or otherwise an especially patriotic customer who required everything be stamped "made in USA"-- we never made an A frame.
 
If 1976 then I am surprised that they are GA0. By then many were GA2.

Did Blackburn start using dodgy-looking painted codes in the last days? Maybe elf'n'safety got nervous about hydrofluoric acid etching.

I am still suspicious. Could they be Ei, BEL or Matsushita remarked by Philips (or someone) to pretend they were made in Blackburn then branded by H-P (in 1978)? Is it possible that the US military insisted on Blackburn, so Philips 'obliged'?
 
First off - thanks for all the help, really appreciate it.

I checked the coding and it is correct. So I guess the tube were produced by Mullard in 1976 and sold to the US Military or HP or some other project and relabeled 6DJ8, made in the USA, and a new date code of 78-16 was painted on. I guess the only part of all of this that is a little perplexing still is the date code. I would think the Army or HP for that matter would want accurate date codes.....
 

maxseeley

Member
2010-03-27 7:58 pm
Thanks!
I will confirm if it is a 4 or triangle!

Yes, the triangle is hard to distinguish sometimes. the best explanation I have found for foreign type tubes is:

Mullard, Philips, and Valvo Tube Codes

Anybody else know good sources of info. for tube coding?

I think that would be a good project for DIYAudio members would be to create a complete reference for tube coding. I would be willing to contribute after the first of the year.
 
The Philips list appears on the web in a number of places, and there are a couple of versions although they don't differ much from each other.

Having failed to find one anywhere, I have been putting together a list for Brimar/Mazda codes. Someone once put a copy of this list on a Chinese(?) site - perhaps he didn't know how to post a link, or maybe he has never heard of plagiarism?