Mullard Amplifier Project

[Joe]

I reckon they are Blackburn, fourth week of January and third week of May 1965.

The Code Book is here: http://golbornevintageradio.co.uk/forum/...p?aid=6443

— Joe

[Yorkie]

That's a useful doc Joe!

[Terry]

The yellow print on those ECC83s is definitely 1960s!

Both were made at Mullard's Blackburn factory in 1965, one in the third week of May and the other in the fourth week of January. Regrettably, the code doesn't reveal the name of the girls who built them!

They decode as follows:

B = Blackburn
5 = 1965
A - January; E = May
3 & 4 = week number

The week number was added to differentiate the 1960s codes from those used in the 1950s although the print was still, originally, white.

[Yorkie]

Don't know if it's an urban myth, but I've read somewhere that the 'yellow' print was meant to be gold, and used in the year of their golden jubilee.

Might just be a load of tosh or audio tomphoolery

[Terry]

Don't know if it's an urban myth, but I've read somewhere that the 'yellow' print was meant to be gold, and used in the year of their golden jubilee.

Hmmm - if my memory is correct, it was a very long jubilee, then!

Philips was founded as a private company in 1891 but became a public company -  NV Philips' Gloeilampenfabrieken (Literally the Philips Incandescent Light Bulb Company Limited) - in 1912, so the golden anniversary of the latter would have been in 1962 ...

It is only recently that the company name has changed although they still sell, if not actually make, light bulbs!

If you've got any valves kicking around that have lost the print or it is indistinct so that you don't know what the type number is, then - provided it is a Philips valve - it is possible to find out from the top row of etched characters. Years ago when I had racks of valves in the workshop I'd take a guess based on mechanical construction - a something CL82, for example - then take an ECL82, PCL82 and UCL82 of the shelf to see which one matched the original.

Fortunately there is another way! 

Someone has gone to the bother of tracking down all the info and has published it here: http://frank.pocnet.net/other/Philips/Ph...ListAB.pdf

In the case of the valves in the pictures, the code is I63. the last digit or symbol is a change or batch code, which can be disregarded. Looking up I6 in the tables shows us that they are examples of the ECC83/12AX7 (as if we didn't already know - but at least it proves that the system works!)

[pwdrive]

A lot of the Mullard yellow print valves we came across in tv's in the 60's weren't very reliable, poor emission as I remember.

Lawrence.

[Yorkie]

Someone has gone to the bother of tracking down all the info and has published it here: http://frank.pocnet.net/other/Philips/Ph...ListAB.pdf

That's the Philips Code Book that Joe quoted in his earlier post #21 above Terry, where he gave the link to find it in the forum Archive.

There's lots of other valve data in the archive too, on Mullard, Brimar, Osram, and Valve Equivalent Guides etc:

http://golbornevintageradio.co.uk/forum/...php?fid=81

[Terry]

A lot of the Mullard yellow print valves we came across in tv's in the 60's weren't very reliable, poor emission as I remember.

Ah, but were they genuine? A lot of shortages occurred during the 60s and manufacturers bought in supplies from other suppliers to fill the gap.

The PCL85 was one and I remember our Mullard rep warning us that they had been offered a batch which, on testing, were so bad that they refused them.

Their intelligence, though, suggested that the same batch had been bought by Mazda ...

The problem is that, unless you looked for the etched Philips codes on the glass to prove that they were genuine Philips/Mullard/Valvo, etc. production, they could have come from anywhere ...

[Terry]

That's the Philips Code Book that Joe quoted in his earlier post  #21 above Terry, where he gave the link to find it in the forum Archive.

Sorry! I hadn't noticed Joe's post when I wrote that ...

I must take a closer look at the archive ...

[pwdrive]

We found that the yellow print PC86's & PC88's weren't very reliable.

Lawrence.