"fruittool"

TIP142/TIP147 *might* be acceptable substitutes although their gain
seems lower.


The design uses an STK350-030 ic to drive the output transistors.
According to the service manual, at idle, the output from the driver ic
to each transistor base should be around 1.2 volts. These new ones are
causing that voltage to drop to around 0.6 - 0.8v, and this is with the
bias adjustment full up.

** That will only make the transistors you have get very hot.


I tried using one of the new ones with an old complimentary one from the
good side and this caused a massive imbalance in the idle bias 1.4v for
the good one and 0.6 for the suspect one. Can i assume from these
voltages that the replacement's are not darlingtons? 0.6v is right for a
single transistor and 1.2v (approximately double) for a darlington?

** Yep.

Non darlington devices in that amp will not only run hot but deliver much
less that full output power into a load.

The fact is you simply have NO driver transistors unless darlingtons are
fitted.


..... Phil