Laney bassamp DB300H

[Stewen]

Hallo !  this is my first topic in this Forum .  A couple of weeks ago , a friend asked me to take a look at his Laney . As I am a "tubeampguy" , I hesitated first but as I didn´t understand how complicated it should turn out , I said Yes . One of the two outputpairs was defect so I replaced both pairs MJ 15003/MJ15004 . A small cap 10uF/50V had exploded and one of the several surfacemounted transistors TR 13 was bad . All other diodes and transistors seemed OK .  The amp worked for me for a short while but suddenly got quiet.  Do You think I shall change the four 4700uF/63VDC filtercaps . They are about 15 years old ?  I forgot to tell , I also replaced a MPSA 42 biastransistor which is in a hole in the big heatsink .
Above and under this biastransistor is a TS8 PNP and a TS 15 NPN . Is it important that these are matched ? And regarding the input-diffstage . Should these two pairs also be matched ?  From "Electronic Experimenters Handbook" ,
about 40 years ago I built a hfe meter . Can I use that to match transistors ?  Well , I have also bought a book about this type of amps .... Douglas Self  , Audio Power Amplifier Design Handbook , and two other books are on their way.
One written by Randy Sloan : High Power Amplifier Design .  Thanks for some comments and advice ...... I don´t want to give up yet.......  ( I use two powersupplies and increase voltage parallell ....)       Regards  Stewen