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.
Nice cheap triode, takes a beating and keeps working, great for projects. But it's very low µ requires a very high driving voltage, 100-120Vpp. Vp of around 175V and Ik of about 60mA will work fine. The Vg will be around -55V. Just keep each triode's dissipation under 12watts. You can get 3watts or so if you only use one triode section.
I built a simple SE guitar amp with that tube. A 12AX7 does the pre and driver stuff. I get around 3watts before slight clipping, and squarewaves at about 16Vpp/8ohms=8watt peak. I suspect the driver is actually clipping before the 6AS7, but havent bother checking it out since distortion is okey with guitar playing. With a couple of 100dB/watt 12" speakers, my kid shakes the neighborhood real good. One cool thing is 6BX7, 6BL7, and 6SN7s fit right into the amp, giving a few variations to the amp. Great for playing around with distorted guitarstuff. The 6SN7 gives less than 0,5watts, and even that screams!
The Hammond 125ESE will work, and any tranny made for 2A3s will work.