Call Lamm or BAT, as they both use the former (and perhaps the latter).
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I think no difference between 6C33C and 6C33C-B is for audio. Just first tube has some longer working perion (a little) but 6C33C are older usually. The second version is more widespread and more "young". Audio companies buy both tubes. Think the choice is matter of taste.
Anton Zverev (www.gstube.com)
I was researching 6C33C tubes and found this thread.
Has anyone noticed a sonic difference or quality difference between 6C33C tubes from Novosibirsk or from Ulyanovsk? I often find listings for 6C33C tubes from these areas and don't know which one to get. I've been told the 6C33C-B were made for the military and the ones to get are from the Ulyanovsk. I don't want to try a set of tubes from each place because it gets very costly with shipping.