Eye witness info from GEC

[Brian Wallace]

Hey Bryan,

Welcome aboard and thank you for all the insight on the tubes we love. I look forward to more insight from you in the future.

[Jeff West]

Hey Bryan- Yes, "Now I've Got A Witness", to quote "England's Newest Hitmakers", good to see you turn up here. I'll echo Brian in saying thanks again for the time and comments, as always. Sorry I've mostly been on the run of late, ironically I just wrote earlier today and then great to find you at large here.

If and when I manage to turn up a specimen of M-OV B339 I'll send it to you to examine.

Formulating additional questions even now . . .

Best-

Jeff

[BryanL]

Sorry guys, the "r-type" link I gave was probably too vague to be of much use. http://r-type.org/exb/exb03443.htm gets you to the B309/12AT7 piccies.
The M-O V one shows an interesting extra top mica; possibly one of the ruggedised QA or CV 4xxx ones. I am perturbed by the 3G---- marking--only because I have seen this elsewhere on tubes, but can't remember on what! The MWT one was unlikely to be an M-O V manufacture, as the seal-off pip is so weak. Probably Brimar. The Marconiphone one is a typical Mullard job, indeed, I'm sure that's a Blackburn code on the envelope. The "r-type.org" home page leads one to "equivalents", where you can quietly go mad cross-referencing!

[Jeff West]

Yep, the MWT B309 with "3G" codes is Brimar, and those are Brimar codes.

We think that those Brimar codes are deciphered as follows:

The first three characters are number (one thru five)/letter/number, indicating: week of month/month of year/year (last digit of year)

Then the four digits after the slash indicate tube type/variant (and with more than one code for various "12AT7" types, etc.)

All credit to saros141/Damon at Artifact audio for developing that potentially testable hypothesis about the codes. Numerous examples that can be cross validated seem to hold up.

If anyone knows of an actual official reference for the Brimar codes or info confirming/disconfirming the above, please post!

Jeff

[BryanL]

Thanks, Jeff, for the info re the "3G" codes. Knew I'd come across them somewhere!

They jogged my memory. Adrian --, a colleague of mine at Hammersmith, also dis-allusioned by his prospects, left to go to Brimar at Sidcup. I've tried, but have not been able to track him down, via Facebook or Friends Reunited; he would have insight to their coding. For what its worth, any labelled GEC/Marconi/Marconiphone/Osram/Emitron B7G or B9A tube with the 3G type of numbering will have been supplied after July 1956. Gateshead was the "miniature" mass production site until then; Hammersmith of course could make "anything", but quantities had to be phased thru the lines at the expense of others.

Your PM re Mullard tubes at Marconi Chelmsford is revealing. I think these must have been supplied after 1956/7. At that time Marconi were producing professional Audio and TV equipment, as well as supplying the military. MOV's domestic audio, tv, radio tube market had been sold to Thorn by EMI, and was now supplied by Ediswan/Mazda. So, I reckon these were replacement tubes for new equipment and maintenance of professional gear. Certainly by 1959 EMI were using Mullard tubes in their TV Camera equipment (E88CCs, EL36/360) and the "P" 0.3A heater series in studio monitors! (These were AC/DC domestic tvs modified to take one-legged (un-balanced) video. A nightmare re hum for the engineers/audio department). Marconi were using Mullard tubes in their sound desks (EF86, ECC83). Both also used GEC KT66s and A1834s(6080s) for loud stuff/power supplies. The Lockwood floor/foldback speakers were EMI's version of the Quad or the Leak, I think.

I see that the CV website http://www.tubecollector.org/cv-valves.htm has been updated. New factory codes appear. There is a mix of "old" and "new" . There were many takeovers between 1956 and 1963. Confusion reigns! Ediswan, Brimar, STC, Mazda, all coalese (like, co-al-ess?) hereabouts. For instance, Ponders End, Enfield, and Brimsdown are geographically within 500yds of each other, so are probably the same factory, with different owners at different times. Sidcup and Footscray are a gnats fart from each other--again, same factory? Gateshead gets KB/EB, after Ediswan/Mazda took over, but I believe the factory was shut in 1957. The MOV production lines at Gateshead were mainly running the same types that Sunderland, KB/EN, was producing for Thorn's domestic Audio/TVs. Mainly 0.3 amp series heater TV receiver stuff, but the mechanical equipment for making anodes, cathodes, and grids for the B3to7-- /12A-7 types was still there.

Well, Easter is over, and there's one more chocolate egg to go!!!!

Bryan