Mullard question

[Edwar65]

Can anyone confirm date these were made stamped 640 r6d/r6e have several that look unused in I think original boxes
Many thanks.

[dougietamson]

Originally Posted by Edwar65

Can anyone confirm date these were made stamped 640 r6d/r6e have several that look unused in I think original boxes
Many thanks.

Could you upload a photo of the codes.

If the date code is R6E that's Mitcham factory May 1956, should have 17mm long anode plates too.
The I have a Mullard ECC83's with mC1 as the manufacturing revision, not seen '640' before.

Doug

[dougietamson]

Originally Posted by dougietamson

Could you upload a photo of the codes.

If the date code is R6E that's Mitcham factory May 1956, should have 17mm long anode plates too.
The I have a Mullard ECC83's with mC1 as the manufacturing revision, not seen '640' before.

Doug

I've just checked my Mullard M8137 'box plate' special quality mil spec version of the ECC83 and looks very similar to yours.
These M8137/ECC83 are sought after by the audio eejits if test good and are matched, matched pairs especially so.

I've attached some photos of various 'long' 17mm plate mC1 & f61 plus some 'short' plate 14mm types I61 plus a M8137.

I think the change to 14mm plates came in 1959 as I have both long and short plate examples from July & August 1959.

The last ECC83 photo has Mullard UK & Holland plus a Lorenz branded Philips made in Germany and a couple of 1958 Telefunkens

Doug

[Maarten]

640 is probably a number from the old code system that was used (from the late 1930's?) up to 1948 on the continent, but for a few years longer in the UK.

1956 was probably the last year that Philips UK used this code system. 1956 in any case was the year the coding on continental valves changed again, into the coding system that lasted until the end of production.

[Edwar65]

Some more photos hopefully just make out codes?