Biasing TwinFace PNP

N

nbw

New member
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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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.
Click to expand...
Are you getting Minus 4.5V on the Collector, not 4.5v as with the NPN transistors
 
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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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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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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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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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