I have tested more than 10 different ST and metal 6N7. Some GT, other simply old ST G ones and metal as well. Both triodes in parallel as usually this is the configuration used as an amplifier driver. Found a good operating point from a distortion perspective around Ia=6mA, Vg=-5.6V. As you can see you should expect getting around 0.09% THD. With some good valves reaching as low as 0.04%, but will have to be hand-selected.
Some 6N7 under test
Great driver from a sound perspective, with low distortion close to a 26 and on average slightly better than the 6J5. Need to review famous 6SN7, but there are lots of measurements for this one out there.
Hard to describe in words what I felt when I played first time “Goodbye Pork Pie Hat” from Charles Mingus. Perhaps it was the due to the fact that I play saxophone, but inevitably for me this song is one of the best ones to test the response of any amplifier. Sax duets, solos, a great bass line and varied moods along the way can take the amplifier to their best of their abilities. Being a jazz fan, couldn’t help myself when listening this amplifier for the first time. I used to play an EL34 push-pull, and liked its sound and power – specially for rock. But when it comes to the first watt, this amplifier is breathless. Pure and a warm tone. Playing this song made me understand all the fuzz about single ended amps. But, far from opening the debate about that, I’m sure that a 45/46 in push-pull has its own merits and would probably will one of those amps I’d like to build in the future.
Having a FE167E full-range driver that have a relatively high efficiency (94dB/W), the 45 SE doesn’t sound low. It has its own personality. Brilliant for jazz, it may need a tad of power perhaps when playing some rock and classic stuff.
7193 valve
It took me some time to optimise the driver stage. Started with an SRPP, then a paralleled 6SL7 to an 6J5 loaded with a gyrator in mu-follower achieving less than 0.20% THD at 150 Vpp. A great driver in my opinion. Now need to replace the 6J5 for the lovely 7193.
It looks like a Frankenstein valve, but it’s a lovely thing to me. Many claim that it’s a superior valve compared to the 6SN7/6J5 or even CV1988.
Adding the 7193 will require opening my 45SE and not having music at home for some time so at the moment is not what I have in mind.
Perhaps when I get the 4-65A up and running? It will take some time for that…
