The 250-ohm trimmer and TR45 governs how much no load bias is applied to each base. It is mounted on the heat sink to sense temperature and also adjust the bias. It’s possible that transister is bad or the adjustment is too high. The circuit calls for a BC311 and since the bias is not separately adjustable for its BC310 mate its possible that your BC161 is a poor match. Sorry, but its been too many years since I worked on one of these.
TR45 is usually a small BC183 or such.
TR44/47 does not have to be matched, as they see the same current flow regardless (more or less – in a working circuit).
Even the output transistors doesn’t have to be exactly matched, really.
The above also goes for them, and their emitter resistors will compensate a little for minor differences in hFe as well.
But the problem in this case is of a different scale.
A DC reading in a “controlled” environment (variac and a couple of multimeters) on the output rail would tell something. As would DC-readings
on the driver transistors.
Replacing components just to see if they burn, will not help in any way.
You need to find out what is really going on.
The idle current should be expected to be around 7,5-15mV or something within that range.
The service manual will specify what’s correct for your model.
But the idle current is not the primary problem in your amplifier. If it’s wrong, it’s because something else is amiss.
Since this is a single-supply amplifier, apprx 50% of VCC is to be expected on the output rail – with respect to ground.
(Hence the need for an output series capacitor).
The idle current should be measured by unplugging the supply lead to the power amplifier for the channel to be measured and inserting an ammeter in between. This should read 100 mA, if I recall correctly. There is a warm-up time for taking the reading. Everything is in the service manual.
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