On a previous post you mentioned that you had adjusted the pre-set bias resistor P5.
Quote:
'I found (on one attempt) that with the resistance turned up on p5 the fuse held but when I turned it down slightly it blew.'
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The fuse could be blowing due to an incorrectly set Quiescent current.
Correct me if I am wrong, IF you were to put a link wire across the pre-set P5, it would reduce the Quiescent current to a low value and possibly enable the amplifier to work.
A faulty or intermittently faulty pre-set would be bypassed and therefore have no effect on the circuit.
There will be some distortion but it might prove a point.
Can you measure that minimum Quiescent current?
How did you measure the Quiescent current previously?
I believe you need to set P5 to its minimum resistance first before you power up the amplifier.
Did you follow the procedure on the Leak instruction manual?