No known cause for one channel to catastrophically burn out -
literally a burnt hole in the board and loss of many components.
At this stage (justified in the event ) replacing the expensive o/p 15 amp
2SA1216
and 2SC2922 with 25 Amp TIP36C and TIP35C; mid power trannies 2SA1668 and
2SC4382 with TIP41C and TIP42C. Replaced low power trannies and passives
and tracks.
Had to change biasing as driven too strong with original Rs but settled
amplifying
undistorted 1KHz, phones only, with variac at 60 per cent of mains.

BUT Every 20 seconds or so a strong short duration power drain - monitoring
on variac ammeter recovering each time without damage. Assuming
high-frequency instability somewhere any
ideas before I blow up another pair of TIP35/36s where to place some hf
suppression ?.
I was just about to isolate pre-amp stage but putting a DVM probe to i/p of
this channel caused signal injection and permanent allway B-C-E s/c of both
the o/p trannies.
The emitters of the TIP35/36s are at rail volts in this amp.
Seems to be mainly DC coupling in this amp so theoretically could be
DC surges in the preamp as I didn't get around to a scope to monitor the
excursions.

electronic hints and repair briefs
http://homepages.tcp.co.uk/~diverse

Nigel,Diverse Devices,Southampton,England