Ok, even I got interested about this one. So, I build it. I used 6111 submini tube (man that's great little lamp!). First, I build a "standard" subcaster with ~20V B+. It's really good sounding preamp/clean booster. Then I add that oscillator and did changes according to frequencycentrals schematic. It works just like tremolo in my Fender vibro champ. And that's not all good thing. First of all, depth (intensity like big F calls it) sucks out alot of tone (highs) and gain. In vibro champ, you can compensate it little with treble pot. But in this case, you can't (in fact, subcaster lacks highs to begin with). And 100k reverse audio pot might work better as a depth. I also have some ticking (just like vibro champ), but I think this can be solved by good grounding. I also did that rate led modification, but it (led) was really dim, and useless. But I don't care those things anyway.

I don't have BC547C transistors, but it works fine with BC547B, BC548C, 2N5088 etc. I also run it with 9, 12 and 20 volts. No big difference. Anyway, speed range is good. Slow enough, but at max. even too fast (for me). It also has a kind of strong feeling in it (depth almost full). I like it alot! Only really annoying thing is that "tone sucking", because I know I have a good sounding preamp somewhere under there. Need to solve this one. It would be so cool to have tremolo and clean boost/preamp in same box. In fact, EA tremolo does this... But I'm a tube brain.

So, there's my 0.02$. Great work mr. frequencycentral!