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In Reply to: RE: Link posted by viridian on March 14, 2021 at 20:35:47
"They're kind of all over the place, aren't they?"
LOL, I'm convinced. In fact, this makes me wonder if the 6AN8 might also be a poor choice. It was originally designed and sold for TV use, and that's one of the big gotchas. Manufacturers were under no obligation to control the characteristics of tubes like these to tighter specs or to cull the ones that failed to meet audio standards. That was the reason tubes like the 7199 and 7247 existed.
At this point, the EF86 is definitely my choice for driver duty. I've tested dozens of them in the past, and they're always very good for THD. And in this position, at this signal level, their modest partition noise and occasional propensity for microphonics in phono and other high-gain applications won't matter at all.
The only remaining decision is how to handle the cathodyne service. It will have to be two 6C4s, a 12AU7 or a 6SN7. Given the transparency of the cathodyne in general, there's probably no wrong choice.
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Buy Chinese. Bury freedom.
Follow Ups:
I'd go with the 6SN7/6CG7/6FQ7 because they are more linear, and the pate-cathode voltage swing is especially large compared to the DC voltage, in a cathodyne.
I was reviewing the CAD layout this morning, and it looks as though another octal like the 6SN7 would be a tight squeeze. The 6CG7 is on my short list. I also have a sleeve of 7044s somewhere, but I'm not sure that moves it in the right direction. This amp will probably be sold when it's done, so I'm trying to limit the selection to tube types that will be reasonably easy to source by the new owner. Thanks for your input on this!
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Buy Chinese. Bury freedom.
I have a couple of Dyna MKiii monos in the que. They use the 6AN8 and I have lots of those tubes, so that is where I am going to start out. Will be interesting to have a listen. I have never had a problem with the triode/pentode tubes as others have. Bad hearing, bad upbringing.....something like that.
I suspect the 6AN8 is at the upper end of the so-called "TV" tubes. If I had an amp that used it, I wouldn't change it out. That's especially true of the Dynas. Good luck with those!
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Buy Chinese. Bury freedom.
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