Hmmm...this does not sound like a tube problem. Sounds more
like one of two problems:
1) a cold solder joint going intermittent; or
2) The volume/gain pot or the MM/MC switch is dirty.
First swap the tubes to see if one of the tubes is faulty.
If not....
I would first try to eliminate possibility #2 as it's easy.
Next time this happens turn the gain knob up/down and flip
the MM/MC switch (make sure system volume is LOW!!!). If you
hear any sort of crackle or channel loss/regain get yourself
a can of Caig Deoxit and clean the pot/switch.
If it's a cold solder I would send the unit in for service.
My old MAC-4100 showed the exact same symptoms. Cleaned all
the switches and pots but no luck. Sent it in for service
and sure enough they found a cold solder joint...it took
them 5 hours on the bench to find it!
like one of two problems:
1) a cold solder joint going intermittent; or
2) The volume/gain pot or the MM/MC switch is dirty.
First swap the tubes to see if one of the tubes is faulty.
If not....
I would first try to eliminate possibility #2 as it's easy.
Next time this happens turn the gain knob up/down and flip
the MM/MC switch (make sure system volume is LOW!!!). If you
hear any sort of crackle or channel loss/regain get yourself
a can of Caig Deoxit and clean the pot/switch.
If it's a cold solder I would send the unit in for service.
My old MAC-4100 showed the exact same symptoms. Cleaned all
the switches and pots but no luck. Sent it in for service
and sure enough they found a cold solder joint...it took
them 5 hours on the bench to find it!