I built the original with 2N3391's:
Then I added the depth mod, which does give you some more control:
But, I didn't understand why the 100k depth pot was put in series with the 68K resistor [especially if you want full depth control] so I simply replaced the 68K with the 100K pot...and it's far better. Now instead of the 68k "cutoff", you can drop to 0k and get some much sharper depth, which is excellent !
...just a quick note if you're goin' for this unique tremolo.