If the trace can center, then the circuit is in balance as far as the + section and - section are concerned, putting the same voltage on the plates.
There is, however, no guarantee that it's the *right* voltage.
I'd center the trace, or duplicate the test conditions in the manual, then go through and check the static voltages on each transistor.? Running each output at, say, twice the current will still give you deflection, but it will bottom out, for instance.
Did you check the emitter supply resistor (and bypass capacitor) for the emitter supply circuits of the balanced pairs?
Harvey
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On 7/19/2021 8:46 AM, Tom Phillips wrote:
Thanks for suggestions
I moved the gain pot slightly but it has little effect.
The power supply voltages are very close to spot on and stable but the four metal output transistors Q610, 20 30 and Q640 are definitely hot. I'm in the middle of a long distance move and don't have another scope handy at the moment to check stage waveforms but if needed are equivalents for motorola ST919/ST7394 available? Casual web search not turning up much.
