Blew up my speaker during repair test, why?

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Blew up my speaker during repair test, why?

Post by Stevem »

Burned and open from power, or just failed construction then crap sound?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
JMFahey
Posts: 252
Joined: Sun Dec 13, 2009 1:39 pm
Location: Buenos Aires - Argentina

Re: Blew up my speaker during repair test, why?

Post by JMFahey »

Something else happened.

1) your JTM45 has NO power enough to blow an EV Force , no matter what it does, not even if oscilating wildly.

2) in any case, the voice coil you show was NOT burnt by overpowering, which would have required 200/250W RMS for an hour or more, but by DC , more precisely a positive voltge, and never by a tube amp (whih has a DC stopping output transformer) but by an SS amp which is direct coupled.

3) I guess in the course of your jobs, that speaker was connected to dead SS amp, which killed it.
Second option: by mistake some bench DC supply was connectd straight to the speaker and went unnoticed.
Where could I have blown up my speaker? I never got any sound out of the amp before the speaker died but I was poking around a lot measuring things. Could I have had some DC get to the speaker somehow? If so, it had to be quick.
Speaker was *already* dead :(
Design/Make/Service Musical stuff in Buenos Aires, Argentina, since 1969
User avatar
sonicmojo
Posts: 669
Joined: Thu Mar 03, 2011 3:41 am
Location: Oahu, HI

Re: Blew up my speaker during repair test, why?

Post by sonicmojo »

For sure it happened while I was working on the JTM45, my nose told me it burned up right then. I'll never know for sure what exact step caused it. Suffice to say it will remain a mystery....but my theory is when my bias supply was disconnected AND the presence circuit was not grounded is when it occurred. I had a bias probe connected to one tube socket and it was showing wild mA swings...only for a few seconds before I shut things down....best guess.....
---------
Bryan
Post Reply