original from pic above:
just got done with a ton of experimentation...
I started with a low leak 80 hfe ge, 80uA leakage with 9.6V adapter. K = K from base to (-). All voltages below are (-)
The transistor turns on at around 2V (collector), which for me was 38K (250K pot subbed for the 68K). The V increases along with K. I actually got a decent tone all the way from 2.5V to to 8.6V (250K), but there is sweet spot in the 5 - 6.5V range (~60 - 90K). The 68K gave me 5.2V. If you raise the V into the 6's, 7's, etc there's some treble loss...which might be better if you think it's too harsh at lower V.
With a lower gain transistor, you'll get a higher voltage on the collector, so you have to lower the K to get that 5 - 6.5V range. The lower gain ones (< 50 hfe) in the circuit are totally predictable...less volume, less sharpness, etc, but still sound decent. ...and it's the opposite with higher gain. In the end, I went with a 2N398A with gain 110 and leakage 100uA. It was a little louder & brighter.
Don't use anything with higher leakage. Just like with the Rangemaster, it adds hiss.
I tried silicon with hfe ~ 130 and the collector voltage was higher than with ge with the same K. So, you have to lower the K to hit the 5 - 6.5V range. For that transistor, I was in the 50 - 55K range for the sweet spot. It really wasn't as bad or harsh as I expected, but I didn't like it nearly as much as the ge transistor.
The silicon turned on around 20K (2.5V), so I can't see any way that 6.8K can be correct if the other values are accurate.
I tried a 3V supply with the 110 hfe ge and it worked right off. The K value for the sweet spot was the same as with 9V supply (~60 - 90K) and the voltage sweet spot was around 2V. Similar to using a low gain transistor, it simply wasn't as loud, sharp or bright...but still decent.
Final version:
