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NPN Ge arrgggghhh


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4/22/1999 11:54 AM
aron

 NPN Ge arrgggghhh
OK,  
 
I went out and bought 60 Ge transistors and didn't realize they were NPN until I got them! I didn't read Jack Orman's post in detail....  
 
OK, other than 30 fuzz faces, what can I use them for?  
 
Is it easy to take a PNP circuit and turn it into a NPN circuit. I assume it is beyond my knowledge and cannot only involve re-orienting the electrolytics and the battery.  
 
Thanks,  
 
Aron
  
4/22/1999 12:13 PM
R.G.

 Re: NPN Ge --- aaahhhh!!
If you don't want them, I'll take them off your hands, and gladly. I do have a use for them.  
 
On the other hand, it really **is** trivially simple to convert PNP circuits to NPN, you just invert the power supply and all the electros and any diodes. Done. You already knew how.
  
4/22/1999 12:31 PM
aron
I kinda knew that but...  
 
In this schematic (Fuzz Face - did you draw this one?)  
 
http://www.ee.ualberta.ca/~charro/cookbook/audio/guitar/fuzzface.gif  
 
Note the change in the 470 resistor to 330. Obviously this is a tiny bit more than just the power supply, diodes and electros...  
 
It's not that the transistors are $$$ - they were only 16 cents each!  
Just that I got carried away and bought 60.  
 
hehehehe  
 
Well, maybe I will rebuild my Tone Bender with these NPN transistors and also build another Fuzz Face with GFR's mods.  
 
Thanks R.G.  
 
Aron  
 
On the plus side, I did have fun measuring each transistor and marking them for Hfe!
  
4/22/1999 12:45 PM
R.G.
The change in resistors was for the change to the BC109C silicon transistors. I regard that resistor as an "adjust to taste" item. Go ahead and use whichever value you like.  
Seriously, you get first order correct results just inverting polarity. Beyond that, it's just optimizing for the specific device, and you do that with *any* transistor where the transistor type matters.  
 
What did you find the hfe's to be?? My ref book says 120 typical, but the mean says nothing about the standard deviation.
  
4/23/1999 5:26 AM
aron
All over the map. Everything from 54 to 120. 120 was the high I believe and a bunch all around 80-90.  
 
I am going to invert my Tone Bender and try them in there. The current Ge Xstrs I have (NTE158?) have too high gain (140-160).  
 
Aron
  

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