[therremans]

Some similarities to my thomson but not identical.

 

[Slade01]

I think the MAZDA brand - they rebranded from different manufacturers. Personally, I used to get great deals on MAZDA branded Telefunken 12au7, and RT (Radio Technique) tubes as well. I also have downloaded valve manuals from EDISWAN - Mazda tubes as well. If they are indeed ones made in France, they would seem to be some kind of unicorn tubes for sure.

 

[Renexx]

Some similarities to my thomson but not identical.

Do they sound different?

 

[JTbbb]

I have been in touch with the chap who tests my tubes regarding the above, and have been enlightened by his response, or should I say, has proved my ignorance . His response is below. As it turns out I have been getting these results anyway (expressed differently) on previous 5998/421a tubes I have sent for testing. I have included a pic of a 421a I had tested a long time ago, obviously low testing, but doing great service in my Bottlehead Crack. 3rd tube down.

So, for those following this little saga! I will be sending the early 1957 “Chatham Electronics/IBM 2399 clear top, rectangular Mica supports, bottom D getters,” which is identical to early WE421A’s, for testing. 1st tube down.

It just so happens that I have another, this one 1958, “Chatham Electronics/IBM 2399, but chrome top, with the more conventional oval mica supports,” which is identical to Tungsol 5998 which will also be sent for testing. 2nd tube down.

I bought these tubes as being tested at 62/64 and 63/64 where 40/40 was minimum good. So this little escapade might prove conclusively that the early clear top rectangular mica 2399 is indeed the same as a 421A. But then again, it could end up proving nothing, which may well be the outcome! But still fun to see!

“regarding the transconductance measurement of the 5998 and 421As it is the same as the TC measurement I give you, but expressed in different units so uMhos (ohms spelt backwards), is the old imperial way of measurement and found in a lot of old valve data sheets, the SI unit is Siemens. A very simple way of converting is just knocking off the decimal points so 14,000 uMhos is TC 14.0 and 20,000 is TC 20.0 etc.”

I have my tubes back from being tested, I also sent a recently acquired 1979 WE421a. All were tested on an AVO VCM 163, and as expected has not proven conclusively that the early 1957 Chatham 2399 clear top with rectangular mica supports, is indeed an early WE421a, even though it’s construction is identical. The results are interesting nonetheless. I don’t intend hanging on to the 2399’s, so if anyone is interested, drop me a PM.

 

[attmci]

I have my tubes back from being tested, I also sent a recently acquired 1979 WE421a. All were tested on an AVO VCM 163, and as expected has not proven conclusively that the early 1957 Chatham 2399 clear top with rectangular mica supports, is indeed an early WE421a, even though it’s construction is identical. The results are interesting nonetheless. I don’t intend hanging on to the 2399’s, so if anyone is interested, drop me a PM.

The "TC" could be various between 11-16 for 5998. Just my 2c.

 

[triod750]

I have a pair of genuine Telefunken 6080 with date code U7211000. The vertical digits are 128 and 137. Are the manufactured October 27th 1971 or...? For how long did they make tubes in Ulm?

(I also have one U4100300 with vertical digits 731. March 14th -60 or -70?).

 

[gibosi]

Ignore the vertical digits. "U"plus 7 digits is all you need:

http://www.audiotubes.com/teledate.htm

 

[triod750]

I have tried to ignore the vertical digits but they are there to be seen . Might they indicate tubes made that date? Number 128, 137 and 731?
I used the information from Brent Jessee but am uncertain about decade.

 

[gibosi]

I have no idea what the vertical numbers mean, but my best guess that they were batch numbers of some kind. And further, it is likely that they had meaning only within TFK. But I really don't know....

TFK began to use this dating system in the late 1960's, and I assume that by the time Thomson-CSF acquired TFK, in 1984, they had exited the radio tube business. So we are talking about the late 1960's to the early 1980's. Further, I have seen rather different 6080's from the 1980's labeled Thomson-CSFS. So I would guess the majority of tubes we will see labeled TFK are from the late 1960's and into the 1970's. And this might be the best we can do....

 

[triod750]

Well, then I decide they are from 1970 and 1971!!
Thanks for your help!!

 

[raindownthunda]

Removed

 

[ostewart]

Any idea if this is a genuine Mullard 6080 - and anyone had experience with them?

 

[therremans]

Any idea if this is a genuine Mullard 6080 - and anyone had experience with them?

It’s an RCA 6080, no experience with them but I wasn’t a fan of their 6AS7G.

 

[triod750]

I guess it's a Mullard if the coding is right. AJ0 is the type code for 6080 and R is Mitcham. 8 and B is year and month. February 1958? 0 is the change code and implies an early batch.

This is my take. Someone knowledgeable will come to your help eventually.

 

[CAJames]

I guess it's a Mullard if the coding is right. AJ0 is the type code for 6080 and R is Mitcham. 8 and B is year and month. February 1958? 0 is the change code and implies an early batch.

This is my take. Someone knowledgeable will come to your help eventually.

Agree the code matches a Mullard 6080 but I don't know about the internals. But it seems like a lot of work to fake for that tube.