# Biasing TwinFace PNP



## nbw (Jan 4, 2020)

I’ve built three of these, they all suffer from the same malady. I can seem to adjust the bias on the germanium PNP transistors I’m using. I am using 2sb33s. These transistors work really nice
y in some easyfaces I’ve built.

I’m far from an electronics neophyte, but this has me stumped.


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## music6000 (Jan 4, 2020)

nbw said:


> I’ve built three of these, they all suffer from the same malady. I can seem to adjust the bias on the germanium PNP transistors I’m using. I am using 2sb33s. These transistors work really nice
> y in some easyfaces I’ve built.
> 
> I’m far from an electronics neophyte, but this has me stumped.


Are you getting Minus 4.5V on the Collector, not 4.5v as with the NPN transistors


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## nbw (Jan 4, 2020)

I can bias the NPN to a reasonable level. I can’t pull the bias on the germaniums below -6.5v I think it’s an issue of leakage current.


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## music6000 (Jan 4, 2020)

The downside of Germanium transistors is they have to be checked for hfe & Leakage to see if they will work .
Typically,  Fuzz Face Q1 = 70 to 85 and Q2 = 120 to 140, Leakage no higher than 200uA seems to be acceptable.
It's 1.27am, I'm off to Bed...
Hey Chuck, Chime In!


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## nbw (Jan 4, 2020)

I thinking he easy face there are two variants one is a single pot no fixed divider resistor, or a much smaller value to account for the 2sn33 higher leakage current ~1ma.


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## music6000 (Jan 4, 2020)

Changing the 33k to 10k might get you in the Ballpark, It will not be typically a PNP Fuzz Face.


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## Chuck D. Bones (Jan 4, 2020)

PNP1 is too leaky.  

If you're going to build pedals with Germanium transistors, you either have to buy pre-screened transistors from Small Bear or PedalHacker _OR _get a transistor tester.  I bought this one on eBay, the board was fully assembled, all I had to do was assemble the clear case. It's a great tool for screening transistors and will also measure capacitors, inductors, diodes and resistors. Runs on 9-12VDC (positive center pin) or a 9V battery.


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## nbw (Jan 5, 2020)

Yep. I think that’s it. Those 2sb33s are specced from building EasyFaces. Those have an SI for PNP1, specifically a 2n3906. I really 
Ike that sound. Maybe I’ll plug in 3906 and make the GE side a hybrid.


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