Is blending power tube brands recommended?

I have some Fisher tubes made by Telefunken (look for the diamond on the base), they are very good. I would not mix brands in a push pull situation though. Swap them out as sets and make sure you check the bias.

I had a 500b model and used the original Fisher branded 7591....if there is a " DIAMOND " logo on d tubes..then it's a diamond sound !! " Telefunken "!!

Btw keep your EH tubes for back up.

Enjoy the music.

Thanks for the input, everyone.
The 500c is autobiasing, and honestly, I wouldn't know how to check the bias on it if I wanted to. I should learn more about that!

After doing a bit more research on 7591 tubes, it appears that just about all of the original iterations were originally manufactured by Westinghouse, and rebranded. So I'm very curious about the possibility of Telefunkens in the 7591 tube family?

Heyraz and Pescolar, are you sure you're not confusing the 7591 and the 12AX7s that are also common in old Fisher gear? Most of my 12AX7s ARE Tele smooth plates, but not the 7591s. Not trying to question your wisdom, just hadn't heard that Teles were even available in that particular tube.

If it's true, do you have a source for them. I do love the Tele sound with the different tubes I've experimented with.

At this point, I think I'll keep running the vintage 7591s I've got, and keep the EHs for back up. Definitely prefer the warmer more dynamic sound of the oldies, even if they are just a tad bit rolled off.

Thanks! And any other thoughts are welcome!
Lincoln

Lincoln- Sorry about that.. The Fisher Receiver I (briefly) had was missing it's power tubes (Estate Sale). Apparently I was in error when I assumed they were Telefunkens just like the 12ax7's. My bad. Good luck.