Aft Preamp

[Jimbo]

Getting going on this pedal. Unclear why there are 4 through holes for an NPN germanium transistor. My understanding is that I am dealing with a CBE standard NPN. How/what gets wired to the 4th hole!?

Thanks In advance for any insights.

 

[Betty Wont]

There are two Base pads for accommodating different transistor packages. use one or the other depending on your part. They are connected.

 

[MacAttack]

Torgoslayer, could you elaborate further on Base pads accommodating transistor packages? I too am building the Aft and was curious about Jimbo's question but haven't had any luck on google trying to catch up to what you are referring to.

 

[Chas Grant]

The EQD bows, which this is based on, uses an OC 139 NPN Ge transistor. Very hard to come by and probably a bit pricy. Many will substitute a different NPN Ge transistor with similar gain characteristics of the OC 139. The OC 139 is a glass pack transistor with the leads in a straight line and CBE arrangement. Most Ge transistor we can get are TO-5 cans with the CBE configuration in a triangle shape. So the 4th hole above the middle B hole is for this type of transistor. The middle hole marked B and the 4th hole above it are shorted together so you can use either configuration with out bending the leads. Only 1 of the 2 holes will be used. Be sure to verify the pin out of the transistor you are using.