Re: Roberts RT7 - problem
As you already measured the voltage at the R26/R27 point as 0.2-0.3V then this should be the voltage you see at the base of both TR6 and TR7, the base current should be so small you should see virtually no voltage drop through the trasnformer windings. If it is not then you either have transistors the wrong way round or there is a problem with the driver transformer or the transistors are broken.
The voltage you measured at the potential divider giving the base volatge was correct.
As the overheating did not occur with the meter in series with supply this may have had enough resistance to stop the thermal runaway you are getting depending upon how good your ammeter is.
Try measuring the resistance of the transformer coils it would then be possible to work out biasing arrangements at it seems the transformer may be faulty causing DC biasing to be incorrect. There are no capacitors that should cause this problem in the output stage.
Jeff
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