There wasn't one that i recall. It's just called a Signature 2000. There's a post above yours of someone else who just saw one. See if he can check it for a model number....
If you need a tube and want to spend $30 for one, then get it.
The yoke is low impedance. I used one for a K4600, but swapped the yoke. I can tell you the rings are attached to the yoke, so if you swap the yoke you have to swap the rings...