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Joule-electra LA-150 Mk 2 dead

Went to play LP's the other day-no sound at all thru the preamp. All tubes are working on the Fosgate Signature phono pre-amp, but the two 6em7's in the Joule pre-amp are burned out.I find it odd that both tubes would burn out at the same time. CD playback is fine so CD player, speakers, amp are all ok, everything is connected properly. Any idea what would have made those two pre-amp tubes burn out silently? No pop or bang was ever heard-one day the phono chain was playing fine-next day zippo. Any help would be appreciated. I ordered two new tubes but am hoping nothing in the circuit was fried.
mrmitch
8 responses Add your response
marakanetz's avatar
marakanetz
5,473 posts
 
Good tube design is the main reason why tube(s) 'die piecefully' without affecting surrounding circuit components.
dob
577 posts
 
" Any idea what would have made those two pre-amp tubes burn out silently? No pop or bang was ever heard-one day the phono chain was playing fine-next day zippo"

I can only join Marakanetz opinion that the answer lies in well thought design of the power supplies. My hat off to Jud Barber....but most of all for the pleasure his preamplifier ("300") gives me during listening to the MUSIC!!!!
atmasphere's avatar
atmasphere
11,615 posts
 
Did the tubes loose their vacuum? Do they still light? What is the nature of the failure?
mrmitch OP
359 posts
 
Thanks guys, I think Marakanetz is on the right track and I trust his opinion after seeing his threads and replies for years here. Dob, have to agree about this pre-amp, its wonderful,better in almost every way from the Conrad Johnson I had before. Atmasphere, no theyre not lighting, just received two new tubes so will try them out today. All the other components work fine but when playing LP's, dead silence-no hiss, no pops, no crackles, nada. Hope its just the tubes, will see later today. Thanks again guys!
mrmitch OP
359 posts
 
Thanks again for your help! New 6EM7's are in and the system is running just fine. Still no clue what made both 6EM7's burn out at the same time, but the big thing is whatever made that happen didnt take anything else out along with the tubes.
marakanetz's avatar
marakanetz
5,473 posts
 
You should know that there are lots of preamps that don't have same reliability... Several models of Rogue, AudioResearch and certainly VTL(champ) may have more complications after the tube's blown
onhwy61's avatar
onhwy61
5,144 posts
 
Would it really hurt to contact the manufacturer about why 2 tubes would go bad at the same time?
atmasphere's avatar
atmasphere
11,615 posts
 
There are not many faults that can cause tubes to not light. In this case I bet the old tubes were also white inside.

If that is true, they lost their vacuum and its simply not possible that the preamp had anything to do with that, unless the sockets themselves are not quite correct for the 9-in noval spec. If the socket bends the tube pins slightly as the tube is inserted, and if you have Chinese tubes (which have glass that is not as rugged as NOS types) then you may experience tubes 'going to air'.
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