My NTE cross reference lists your MPSU05 as a NTE188, NPN High Voltage Amp, TO202 cas style .5 amp....(compl to NTE189, PNP). I guessing it's in a push-pull amplifier. NTE is one of the most common brands found in retail electronic stores. Also of help, mouser.com with no min. order and NTEInc.com both for online crossing.
Good luck, Jere