[Phlogiston]

Looking further in the manual - not the Hickok tube chart - there are differences in:

6J5/6J5GT
6F5/6F5GT
6Q7/6Q7GT
6K8/6K8G/6K8GT
6SN7/6SN7GT and more in 6SN7GTA


But NOT in:

6K7/6K7GT
6R7/6R7G/6R7GT

Probably more examples. Need to watch closer for this.

One explanation for not noticing before is that I always use the factory spec tubes and most always try to use the factory brand or the brand that they used. AND that Hickok (for one) does not differentiate on most of these.

P.S. actually, I guess that I did notice, just never took the time to figure out why.