which BC108 for a silicon FF

[yeeshkul]

I 've been told that there are BC108A,B and C where the letter follows the gain of the device. "A" is the weakest. I have BC108C with gain of 750 and that seems to be a bit too much. Does anyone know what was in the original units in early 70s?
Thanks

[GREEN FUZ]

I believe the originals sported 108c`s but I would be tempted to use a b for a bit less gain.

[MetalGod]

The BC108s I have don't have a suffix - they're all around 150-200 Hfe.

I'd keep the transistor gains lowish for a true FF tone.  If you put some higher gain transistors like the BC109C in there they take on a kind of Big Muff tone.

[Bernardduur]

They have a suffix

I read that the C version was used; yes, high gain!

[George Giblet]

I've got stuff written all over the place for fuzz faces, unfortunately I haven't looked at it for a few years and there too much to read.

The best summary notes I found:

- Transistors high gain silicon
- Upper resistor 330R (not 470R from the Ge version)
- Earlier units had 8.2k collector resistor but later on this dropped to 6.8k; the lower value biases the transistor better
- the output cap is 10nF  (some schematics show 100n)

More Details

Si units Late 1969-1975
Si units use 330R and transistors: (in this order over time)
BC108C, BC183L, BC109, BC109C, BC209C
BC108C, BC183L used 8k2.
BC209C units had 6k8 not 8k2, othe BC109 unit may be same- not sure.
1973 was a BC108C

BC183L units reported to get 4.5V on Q2 collector if 8k2 change to 6k8,  this agrees with simulations with medium-high gain.
5k6 is probably better.
One guy used 6.2k and this is very close to the mark.


[There are non suffix versions of BC108 etc - I have heaps of them.  Technically they could the gain of any suffixed part.  The one I see tend to be in the middle of gain range, lilke MetalGod found.
]

[yeeshkul]

guys thank you for your replies