OK, I found these
- http://www.ebay.com/itm/Matching-pair-of-NOS-NIB-Mullard-ECC33-tubes-/281032405980 — fX1 B7K
- http://www.ebay.com/itm/Matching-pair-of-NOS-NIB-Mullard-ECC33-tubes-/281044251955 — fX1 B7K
- http://www.ebay.com/itm/ECC33-Mullard-B65-CV2821-6SN7GT-yellow-print-rare-/300840596483 — fX1 B7K
- http://www.tangotubes.com/ecc35.htm — the first ECC33, fX. B.. I guess
all apparently fX-coded, possibly even fX1-coded, but they all claim to be ECC33, not E33CC, tubes. All of these are also of the tall-base skinny-bottle kind but the base color varies. Note the 7 that is 1957.
Then there are these
- http://www.akh.se/tubes/htm/ecc33.htm — 5K1 B5F
- http://www.sanyue.net/bbs/read.php?tid=6948324 — 5K1 B5G, 5K1 B6E
- http://www.erji.net/read.php?tid=1274026 — 5K1 B5E
- http://www.erji.net/read.php?tid=1260029 — 5K1 B6E
all of the short-black-base fat-bottle kind. Note the fives and sixes of 1955 and 1956. There are older ECC33 tubes with Mullard-only numeric codes. Are they all fat-bottled like these 5K1s?
The saga continues. Apparently there are also (at least) 5K2s and 5K3s as claimed by the following.
- http://www.ebay.com/itm/ECC33-MULLARD-in-box-new-/130776960452 — 5K2 B7J3
- http://www.worthpoint.com/worthopedia/mullard-cv2821-ecc33-6sn7-163014808 — 5K3 B7J4
Now these are not 1957 codes, so we seem to have arrived to 1967. Again tall-base skinny-bottle tubes with varying base color.
Obviously I'm just guessing based on limited evidence but it seems possible that fXs were made only for a while between 5K1s and 5K2s.
What are the codes on your ECC33s, everybody?
By the way, this thread could use some ECC33 photos.