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The colour code was only used for a limited period of time...

Hello cbes!

I do not dispute that the colour code was used in the early 1960ies for depicting a set of properties of Philips/Valvo SQ valves.

BLUE was used for valves for aviation applications.
RED was used for valves for industrial applications.
YELLOW was used for valves for PTT and generic telecom applications.
GREEN was used for valves for computing applications.

E88CC were meant to be used for industrial applications and therefore colourcoded red.

CCa - which are electrically equal to the E88CC - were meant to be used for long duration PTT apllication.

Both types were manufactured to the same specification on the same machines. The difference was in the batch testing and burn-in which was much more stringend for the CCa, to fulfil the PTT reliability requirements.

In the second half of the 1960ies the colour coding of the stamps was abandoned and all Valvo SQ valves were stamped white again, as it was done before the introduction of colour coding in the 1950ies).

The properties (longlife and/or interface layer free cathode, tight tolerances, vibration resilience, long life and/or high reliability) of the valve types involved were retained anyway, with or without the colour coding.

If you need confirmation for that, use similar sources to mine:

(1) Valvo Valve databooks 'Spezialroehren', various versions published between 1954 and 1972.

(2) An extensive stock (hundreds) of Valvo SQ valves from various sources and production batches, acquired between the early 1970ies and now.

(3) Philips typecode lists

(4) Valvo application notes

Regards,

---mb---
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