BC109 doubts

[copachino]

Hi, i want to build a tone bender MARKII, with the BC109 metal case transistor, but im not sure if this transistor are biassed as normal silicon transistor or this are like the old schoold GE that are not consistent in the gains..

[Nocentelli]

BC109c works great in a mkII type silicon build. I've never bothered testing and sorting them, they seem to be fairly consistent. Skreddy uses them for the lunar module, which is sort of like a mkII with a high pass control between the 1st and 2nd transistor and a treble roll-off pot on the output. It also works well in the DIY "Hot Silicon", another mkII-ish circuit.

[copachino]

do you have an schematic for this transsitor for the MKII, i want to start today jjeje

[Nocentelli]

I don't have a definitive BC109 MKII schematic that I would use, but the "standard" silicon mkii schematics, whether solasound, vox or other (e.g. found at fuzzcentral) will work with the metal can 109c. If you look at the numerous mkII variant schematics, e.g. Lunar module, hot silicon, GGG's mkII tonebender etc etc, they all tinker with a couple of spots in the original schematic: The biasing arrangement of Q1 (generally adding an emitter resistor, with or without bypass cap, and a B-C resistor to increase stability), the value of the Q2 collector resistor (33k/47k/56k ish), and the exact combination of collector resistor values on Q3 collector (e.g. 470r/8k2 stock, 2k7/10k in the lunar module). The voltage feedback biasing resistor from Q3 emitter to Q2 base also has a cool effect on the amount of saturation, with 100k and up giving full-on compressed filth, and 56k and under giving a tighter, more defined fuzz.

If you're breadboarding, I'd suggest either trying out the stock Si MKII schematic to see what you think, then tinkering with the aforementioned areas if you want to experiment further.

Alternatively, if you want to just choose and build a circuit, the hot silicon and Lunar Module both sound great as they are; Hot silicon is a rough and edgy simple three knobber, the LM is much smoother and more refined, and can have 5 controls for maximum tweak-ability.