api 2501 three transistor boards

Hello,
A friend gave me a bunch of little circuit boards desoldered from an API console. Some might be broken, but some might be ok. They are labled 2501 and contain three smd transistors and a couple of other smd parts. They have 5 connections.
These might be matched pairs with current source?
Does anyone have some info on these parts?
There is also one device, also a little pcb with 3 Transistors and some other parts. They are through hole components. The thing isn´t labled at all...
Thank you very much!

Buffers?  Trace it out and compare to the ones in the 550 EQs.

wonderful, thank you!
I compered it with this schematic:
http://www.hyperspasm.com/hyperblog/wp-content/uploads/2009/03/550a.pdf

The resistor values match the values in the diagram for the amps A3-6.
Seems to be it!
I can´t check what those transistors are.... one has a 20 on it, the other two have a 10. But i´m sure it´s the part.
Only thing is, my parts have 5 connections. Not 4 as in the 550 schematic.
I´ll try to trace it, difficult since it´s so tiny...
I have never seen anything like this. Are these custom api parts?
All of this makes me want to clone the 550...