Yes to 7591 = Octal, but the 7868 is larger than an EL84 (same diameter as an octal tube) but with a 9 pin base.Originally posted by Old Tele man
...same tubes ELECTRONICALLY, but totally different packaging and pin-outs:
7581 is 8-pin OCTAL and same size as 6V6
7868 is "special" 9-pin NOVAR and similar in size to EL84
7581 was a typo on Tele's and my part. We both meant 7591 and the information stands as stated.Originally posted by 57special
Yes, but he asked about 7591's, not 7581's. I DO know that they were both used in the same models of certain 60's Ampeg. i.e. a Reverborocket or SB12 Portaflex. I think the pin outs are different, and that the 7591 is a more robust tube (can deliver more power when maxed out) than a 7868.