here it is from the website
> William, Valvo used five colour codes for labeling. These are:
> white - general purpose, consumer applications
> > general reliability, medium tolerance and life expectancy
> red - industrial control, professional services
> > long life and reliability, close tolerances, shock and impact
> (usually three micas and other reinforcing measures),
> interference-free special cathodes
> yellow - PTW applications, this includes everything were tubes are
> located in remote/inaccessible areas
> > long life and reliability, close tolerances; no need for shock and
> impact proofing as well as interference-free cathodes in these
> green - calculator/computer use
> > long life and reliability, close tolerances at certain
> points, interference-free special cathodes; no need for shock and
> impact proofing in these applications
> blue - navy and airforce applications
> > reliability, close tolerances, shock and impact proof (usually
> micas and other reinforcing measures), interference-free special
> cathodes, filament impervious against repeated turn on/off cycles.
> Interesting to note that the armed forces did not specify extended
> lifes of their tubes!
> Common for all colour branded tubes is their long life of > 10k/h,
> if not specifically mentioned.
The US Navy did not specify long-life tubes at this point in time because they retubed completely after every tour of duty. After the war the new Air Force began requesting shock-proof long-life tubes, and the Navy followed suit, initially for use in submarines. All branches of the service got into the act shortly afterwards, but eventually the use of solid state devices made this irrelevant. Can't remember where I read this, but that's the gist of the story. If you want some interesting reading, get your hands on some of the specs for the myriad of tubes the military is currently using. Sorry, haven't kept any links.
Please see the following page in our club.
Hong Kong Tube Audio Club
Pls use the following link instead.
Hong Kong Tube Audio Club
Also on Tim's Hong Kong Audio Site, the best and most complete 12AT7 shootout I've ever come across. Like Joe's Tube Lore, for us old CJ users. The observations and recommendations are pretty darn accurate.
Quoting a friend who used to work for Valvo in the design department:
"-rote Serie-! Valvo produced long-life tubes and marked them with colours like blue, green, yellow and red. This tubes had special kathodes."
the 'red series' stamping was applied from the late 1950ies to about 1965/66 for industrial grade valves produced by Philips (Heerlen, Sittard, Valvo Hamburg, OEM) - after that the stamping was changed to white again.
The colour of the stamping is no indicator for the quality ov the Valvos - if there is any at all, then it is the decyphered two line etched batch code near the bottom of the valve.
If the second line beginds with a D, then it is a Valvo Hamburg valve.
More likely it is to begin with a DELTA for Philips Heerlen factory.
Both is fine.
You are right that red series or any valvo label tube could be from Valvo Hamburg or Heerlen or other Philips sourced tubes.
However, color codes meant something is the jist of the posts in this thread. The point here is that VALVO RED and other color codes related to different specs, and THAT IS an indicator of the quality parameters like mtbf etc.
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
You are right that the color coding was abandoned in 60's and other identifiers were used to specify tubes. Most old tube hands are aware of that.
I'm concerned as to tube life and any possible effect on sound. If you think others would enjoy the specs, then, by all means.
For example, low noise parameter is something you can relate directly to the sound. Others may be less relevant as far as the so-called "sound" is concerned.
Perception of sound, and psychoacoustics is a complicated and controversial subject. Some people seem to perceive differences with different things like the tube architecture; Cryo treatment, era, color of the plates and even getter type etc etc., and others do not.
Best judge of the "sound" is you and your system.
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