I got the ALPHA 77 SX up and running.
Problems were: Both tube filaments burnt out, electronic bias was not
working properly, and warm-up timer running too fast.
The fix; two new tubes, removed a number of modifications someone made to the
bias system circuit board and brought the board up to date with the latest
board design .... Added a bias threshold pot. Electronic bias now operating
correctly. The warm-up timer was also running fast ... about 1 minutes and
30 seconds rather than 3 minutes.
Bottom line, the amp was going to the 8.1 vdc operating bias after 1 minute
30 seconds ... the tubes experienced loading before proper filament warm up
resulting in the tubes' premature filament burn out.
73,
Bob
K8MLM
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