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RE: final update ....

Posted by vinnie2 on June 9, 2017 at 15:13:22:
Hey Tom
Could you expand upon "That being said I would guess there are some issues somewhere in the chain to not hear differences in the 2 amps"? Quite frankly I am looking for an explanation. Especially now as I just got through doing an A/B with the 6bq5 and the 45 and got the same results as the A/B between the 6bq5 and the 813. The 45 is all dht. The 6bq5 has a triode driver and a pentode output mode. Both are SE.
Let me state the test conditions
1. Only one set of speakers was used, my Altec Granadas to be exact.
2. Very careful adjustments of volume levels were made before the test began; there was no audible difference in volume when switching between the two amps.
3.Only one source of signal was used, a direct feed from my cd player that used a pair of y-splitters to take the signals to each amp. Both amps were on full time.
4. A switching unit was used that had both amps as inputs and one output to the speakers.
5. A load resistor of 10 ohms/30 watts was placed across each pair of speaker terminals in addition to the speaker connections to make sure the amps could be switched hot without damaging them.

I also used the same set up yesterday when A/B testing the 6bq5 against the 813.

In all cases there was no audible difference to my ears between either pair of amps in either test, except that the 6bq5 seemed to have a tad bit better base. It may be my old ears are not hearing the higher end of the the scale, but if you look at the links below in my reply to cpotl's post, you can see that that still leaves a lot of music that I should be able to hear.
I read in the one link on "do amps sound the same" that one of the biggest factors in them sounding different is distortion, and in particular which harmonic it is in. Anyone used to SE amps is most likely familiar with the fact that the distortion from a SE amp is less disturbing than from a push pull amp because of this. To me it seems reasonable to think that if this is one of the factors in amps sounding different, if all the amps have the same distortion by being SE, then they might sound very similar in an A/B test.
To test this theory, my plan is to next build a simple diy pp 6bq5 amp and repeat the test between the 6bq5 se and the pp amps and see what happens.
In the meantime, if you know of any other contributing factor for me to check out I would appreciate hearing about it.