A couple of Mullard valve questions.

[VT FUSE]

I am sure that the answers that I seek are straightforward,however those members with far greater knowledge than I,should have answers.

I have taken delivery of a few sleeves of ECH83 Valves manufactured by Mullard and the Valve boxes carry the statement that they are not licensed for sale in Gt.Britain,the actual valves carry no country of origin whatever. Etch codes are YDDZ912. My initial thought was that these may be Philips Valves made in South Africa during a period of trade restrictions? They have the folded cruciform lines at top of envelope that indicates Philips group parentage.
Can some kind person suggest what the likely real truth is?

I also note that quite unlike many other ECH83,EBF83,EF98 etc in my hoarde,these particular Valves are totally lacking the metallic reflective coating on the inside of envelope that almost totally obliterates the perforated mesh screen.
I appreciate this is not the Getter deposit (present near exhaust tip of this type of construction) and have often pondered as to why some Valves have this characteristic silvering? Is it a product of Cathode conditioning process and is it Barium? clearly it is deposited after the electrode cage assembly and mica stuff washers are built into the envelope.Even the EF50 displays it when not in its can.

Thank you

[G8HQP Dave]

YDD seems to be ECH81 (YD) version D - which confirms that at least some ECH83 are actually selected ECH81.

Z912 probably means made in Philips, Monza in January 1969(?), second week.

The metallic coating you mention probably arises from the cathode activation. It is oftrn missing (or quite small) but some factories seem to produce lots of it especially in the later years of the valve era.

[VT FUSE]

Thank you for the info Dave.
You have confirmed my suspicion that the deposit is resulting from cathode ageing/activating process and is presumed to be evaporated cathode material.

Agree on the ECH83 being a tested subset of the ECH81 and have confirmed this by a back to back test in two Valve/hybrid car radios where both worked but the ECH83 had a slight benefit at HF end of MW band and guess this would be more pronounced on
continental radios having SW provision.

Appreciate the useful and no doubt correct answers given.

[G8HQP Dave]

I have some EF183 with lots of metallic coating inside. I think these were branded Mazda, but made by Tungsram in Hungary? (working from imperfect memory here!) Most similar valves just have a little silvering adjacent to anode holes, so why some factories/designs had lots but most had little or none I don't know.

[VT FUSE]

I have long wondered about this,some brands such as Telefunken with solid cylindrical screens have none (or very little) of this coating but I guess as these are low power signal Valves any effect on IR cooling is of little consequence.

My knowledge is way below that of Physicist but did wonder for years if this ?evaporated metal ends up on grids and mica insulators resulting in leakage or secondary emission.

I have dim memories of Tung Sol papers on "space charge"(!) Valves mentioning Valves having undergone special cathode processing during manufacture. Some of the RF/IF Pentodes are very high slope when compared to European types,thinking of 12DZ6 for example,and these are not silvered only Gettered.

Your wealth of knowledge and insight is appreciated-Thanks for responding.

[emeritus]

Companies sometimes licence manufacture in other countries (often where the goods will be sold at lower prices ) with a condition that they are not to be sold in the company's home market. You sometimes find this sort of notice in books: several of my older Penguin paperbacks have warnings that they are not to be sold in the USA or Canada.

[VT FUSE]

Thanks for that explanation emeritus: your answer would certainly fit very well,having read about the BVA cartell that operated it sounds more plausible than my guess.
I appreciate your input too.

[Maarten]

Is the small printed code actually YDD Z9I2 (with the letter I)? Is the Mullard brand stamped on the valve?

[VT FUSE]

Hi Maarten,checked all 5 Valves from the sleeve and the boxes are a little "age tired" they all bear the same YDD Z912 etch code (numeral1) and carry the old style Mullard shield but no indication on boxes or Valves as to country of manufacture,the boxes boldly read: Not Licensed for sale in G.Britain and are the old format box and livery except for the usual origin such as Made in Holland/Gt.Britain/w.Germany.

Mullard sleeve number 2 (not discussed up to this post) 5 x ECH83 Late style M logo,made in Holland etch codes ?Haarlem triangle followed by YDE 5D2
Philips .. .. 3 ( also not discussed) 5 x ECH83 simple PHILIPS script below which: ECH83 etch codes YDE ?Harleen triangle & 3A4

Any and all info much appreciated-thanks!