unknown tubes! Probably Mullards

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Post by dotfret »

Thanks to P_christov for seeing that, I couldn't see a code at all on my clunky old computer. Now I'm in a different location on a new laptop, it is as plain as day.

Yes, that's a delta mark for Philips Heerlen. Try the fridge test and see if the line above is revealed (should be I63, might appear to be 163). Plenty of those sold marked "Mullard Made in Holland".

While we are talking about this, I looked at a lot of Japanese 12AX7 in passing today, Toshibas (Philips tech) and Nationals (RCA tech). They all have nicely rounded plate lugs - so there is another distinguishing factor for the next ID challenge ...
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