I am having fun repairing a NAP 160 and have to replace a MPSA56 transistor. Can I fit any A56 or must I match it to its sister MPSA06? I can measure hfe with my multimeter. The 5 A56 I have purchased have hfe from 120-135 and the 5 A06 (purchased in case I have to fit matched pair) measure 156-175. How close do they have to be? On a more general note, which transistors on the PCB have to be matched in this way?
Posted on: 09 July 2002 by Manu
No need to match.
If you want to match something, match all corresponding trans from channel to channel.
The only matched trans are the input ones.
Emmanuel
Posted on: 10 July 2002 by John Luckins
Matching will be virtually impossible if one set are NPN and the others PNP. It is not just Hfe that will be a different range, Ft and the junction capacitances will all be different. The PNP's are slower.
It is probably best to get the Hfe 's as close as possible. If the stage gain is high compared with the Hfe then matching becomes important, but this is not normally the case in good designs.
John
