Transistor Matching

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z 1975, 2010, 2011 Nyle Steiner
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Function

This PCB has no panel, no case, just the PCB. It is only for those who want to match their own transistors and want a PCB instead of having to Veroboard it. It has 2 spots for an 8 pin DIP socket. One for PNP matching, one for NPN testing

Use

Put the transistor you want to test in the 3 pins of the socket that correspond to the type of transistor, marked TEST Q NPN or TEST Q PNP. The NPN has two separate locations with different pinouts. One for the 2N5172 pinout, ECB, and one for the more standard EBC. Only install one transistor at a time in these two sockets.

Measure the Vbe at the appropriate connector. Mark it down. Test another, and another, and another, etc. marking down the Vbe. Pick two transistors with a Vbe within 0.002 volts. You're done.

Do not handle the transistors with your bare hands or anything that is not at the same temperature as the transistor. Use pliers with injulated jaws (some tape should do) to minimize any heat transfer between the transistor and pliers. Let the transistors to be tested sit somewhere and stabilize before testing.

Component Selection

See the Component Notes page for more information.

Resistors

I recommend using 1% tolerance, metal film resistors everywhere.

ICs

The PCB calls for an LM741. Use and good comparable OpAmp.

Transistors

Use standard small signal transistors. You aren't comparing to the transistor on the PCB, you are merely establishing the Vbe of the transistor you are testing. Make sure both of them are at room temperature. A fan blowing over them, letting them sit at operating level for a minute before measuring is a good idea.

Sockets

You can use these from Mouser, or just cut up a regular IC socket.
Mouser #535-03-0513-11H
Aries #03-0513-11H

You can buy these in a lot of different lengths and they are designed to be able to break them into the desired length.


Build Notes

Soldering

I assume you know the basics of soldering. I like to insert the low lying parts first, like resistors, diodes, etc. After these, I install the IC sockets. Next capacitors, transistors, connectors. Use a good solder, either an organic flux, which you should wash regularly, or a no-wash flux.

Take a break every so often, wash off the flux if you are using a flux which required cleaning. Double and triple check orientations, pins, and solder joints.


Component Placement

The PCB has a silkscreen for two SSM2210s. Ignore this. Put a socket in the spot and "permanently" install a generic NPN and PNP transistor in the socket side opposite the silkscreened TEST Q NPN or PNP, PNP at the PNP test socket, NPN at the NPN test location. Install some stiff wires or an MTA connector at the + PNP and NPN + locations to allow connecting a volt meter. You need a meter which will at least read to mV, and 1/10ths if possible. Match to no more than 0.002 volts.

It has 4 holes into which you can install some standoffs or mount it on a board or something. Be creative.

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Schematic

Values

Names

BOM