Low Gain Silicon Transistors

yes... in the Silica fuzz there are two transistors - lower gain - with a trimmer to adjust the HFE.... I am wondering how is this measured to get to the desired HFE?
 
I've been experimenting with piggybacked transistors the last couple days.

2N2369, 2N4123, 3903s (hfe 70-90) etc of course all work in a FF, but I think I am hearing something 'different with mid-gain devices dialed in with piggybacking. Something maybe more complex with the texture, especially in Q1.

But at the same time, I've read on other forums that the very pioneers of this technique (RG Keen, "Brett" ?, and a couple others contributors) lost interest in it once the aforementioned low gain devices were identified.

Have you guys found piggybacking to be something significantly different / useful vs run of the mill low gainers?
 
I have a box of Russian germanium NPN transistors that had too low HFE (40 to 70) for my pedals so they sat there unused. I think I will see what I can get from them in this circuit on the breadboard.
 
necro. Here's a chart from some piggybacking silicon NPNs (using the example schematic I linked long ago). Unmarked (probably Central) 2N3904s, initial gain listed in the chart, but generally mid-200s. Final beta/gain dependent on R resistance. General flow: lower resistance, lower beta, follows a log curve. 4k7 is around 16, 10k is around 50.

I can't do the math in my head, so I just made a chart to have a visual on approx. values.

NPN BJT Piggybacking betas.png
1769717252878.png


Then I thought to try another band of gain, this time 2N5551 (easily gotten at Tayda and elsewhere), gain levels in the mid-100s. Anything below 8k2 wasn't registering as a transistor. But as expected you have finer control the lower your Q1 and Q2 initial beta is:

Beta vs. R (kOhm).png
1769717207396.png
 
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