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RE: 6SL7

Posted by drlowmu on March 20, 2017 at 08:53:34:
Hi George,
The simple answer is : there are NO pin alternatives to the 2A3 pin arrangement.
The two-stage DC circuit's primary gain is from the driver, where driver choice and implementation is most urgent when seeking perfection.
My entire response addresses, and is entitled " 6SL7" and all pin comments were referring to an octal socket's pins. That would be the 6SL7, where alternative better choices exist.
As examples of three "non-octals", with linear graphs and mu of 100 : 1/2 12AX7 as a 9 pin mini, 6AV6 with symmetrical plate as a 7 pin mini and diodes tied to plate, and a 7B4 seated in a loctal socket.
There are compromises in any and ALL choices of high mu driver tubes for a direct coupled JJ 2A3-40 amp.
For example, the latter two tubes I mentioned are more microphonic than the first tube mentioned, but when employed just one time on the input, its OK in real-world use. The latter two tubes have symmetrical plate-filament-grid structures. All three tubes given as examples, are mu of 100, thus are preferable, normal listening-wise, to a 6SL7 octal-based tube IMHO.
Jeff Medwin