I'm no expert, but yes, seeing that they are all 7951 it is safe to try. 1 EH & 1 Fisher on each channel set up to mirror the other channel.
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I would think that power tubes would need to be biased wheb they are put in. If you change them, you would need to set bias voltage for the different tubes. I trust you noted the locations of the oeriginal tubes. If your unit is not biased you will need to do so, as you could burn up your power tubes more quickly.
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!