WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
I built two SE amps with it, "FireFly Single Ended Tetrode" and a PP amp "Sven 6P1P PP".
In addition there is info in the Meng Yue Mini thread.
I just looked up the Sven 6P1P PP Amp thread, and that amp has been running for three years now as the main upstairs amp. I've never gone back and touched anything in it. I should clean up the PS (change from 1N4007 to lower noise diodes) and try LED bias for the input stage.
Here is the specs for comparison. I agree that all three tubes are similar, but believe they were each designed individually and none is taken from the other. Look at the mechanical construction and one can see that the 6V6 plate would not fit either of the other two envelopes. Likewise the 6P1P/-EV would not fit in the 6AQ5 envelope.
Both the 6AQ5 and 6V6 have much higher max Ik as both were designed for vertical deflection service as well as to be used for audio output.
The 6AQ5 is a beam power pentode, the 6V6 is a a beam power pentode, and the 6P1P/-EV are Tetrodes with the characteristic kink in the plate curves.
6P1P 6P1P-EV 6AQ5 6V6
Va 250 250 275 315 V
Vg2 250 250 275 315 V
PD 12 na 12 na 12 10 12 9 W Pent/Tri
G2D 2.5 1.3 2 2 mA
Ik 70 70 115 105 mA
EL90 and 6AQ5 are different names for the same valve. Whether it is implemented as a pentode or beam tetrode may depend on the manufacturer. 6V6 is usually a beam tetrode; it was developed as a cut-down version of the 6L6.
I think some ebay sellers offer the 6p1p as an 'EL90' but it can't be as it has a different base. It may be electrically equivalent. There is also the 6BW6 which is a Brimar 9-pin 6V6-alike; different pinout from 6p1p IIRC.
Apart from minor differences like capacitances and maximum power dissipation all these valves can be regarded as the same, so any circuit for one can be used for any other.