ECC40 - Preliminary impressions:
I have been living in ECC40 land for some time now, with 6 tubes in house and 5 more on the way. My thinking is these are essentially 6SN7s in a different bottle: that is, Philips 6SN7s if you will. The ECC40 was introduced by Philips in 1948 to replace the 6SN7GT. However, as the ECC40 was among the first of the all-glass construction vacuum tubes, the micanol octal base was discarded in favor of the glass rimlock B8A base. Evidently, the rimlock base never really took hold, as it was soon replaced by the ubiquitous B9A base used in the production of 12AUX7s, 6DJ8s and many, many others. Even so, Philips continued to manufacture the ECC40 on a rimlock base well into the 1970's.
I currently have tubes manufactured in Chartres, Sittard, Eindhoven and Hamburg, and notice the same country-specific sonic signatures we have noticed before. The ECC40 manufactured in Chartres, warm with rather punchy highs, is similar to the ECC88 manufactured in Suresnes. The Hamburg-made ECC40 has a similar sound signature to the Hamburg-made ECC88s, a bit dry, with nice airy highs, but not as punchy as the highs on the French tubes. And the Sittard-made ECC40 most strongly resembles the Heerlen-made ECC88 and E80CC. (I am told that Mullard manufactured the ECC40 in Britain, but have yet to get one.)
In the early 1950's it appears that there was a cluster of perhaps 9 distinct factories and/or production lines located Eindhoven, each with a distinct factory symbol. To date, I have seen ECC40s bearing 5 different Eindhoven factory symbols, and possess three of them. I have yet to spend any significant time with these Eindhoven tubes, as I have a couple more coming, and hope to evaluate them later as a group. However, based on first impressions, they appear to be similar to the Sittard tube.
While I am still in the process of evaluating the ECC40, I can say that the Sittard-made ECC40 is very comparable to the Heerlen-made E80CC and Sylvania 6SN7. In other words, it is already one of my favorite tubes. And for those with darker systems, the Hamburg-made ECC40 may well be spot on. Yes, you do need a rimlock adapter, but I think you will find these tubes to be well worth the trouble. Highly recommended.
1953 Dario (Sittard-made) ECC40