JCM 800 blowing fuses again.

[kingsxman]

I picked up a jcm 800 2205 used. It came to me and would immediately blow the 3 amp fuse. I put in new power tubes and the probem went away. I DID bias the amp by the way... 37 ma if memory serves me correctly.

Long story short I have played 2 full gigs and 1 partial gig with this setup. I was playing the third gig last night and at the very end of the night the amp starts blowing the 3 amp fuse again. 2 times in 5 minutes. The only thing thats different than the last gig was that I put a new celestion speaker in the 2x12 cab...otherwise thats it.

Could my new power tubes be going bad? They are GT-6CA7GE. (Groove tubes).

THanks in advance.

[kingsxman]

OK. Here's the scoop:
I took the amp and tested it today. I pulled the back off and watched the tubes as I applied power. When I turned the standby on...one of my power tubes flashed brightly and the fuse blew. I pulled the tubes and tried again. No problems. With standby on the amp ran for 5 minutes. I then put the tubes in again...reversing the sockets. The power tube that flashed bright before was still the one that flashed again and the fuse blew.

So now, the question is....is the amp causing these tubes to go bad....or did the tube just go bad? This IS the 2nd set of tubes that I've gone through on this amp. THe first set was bad when I got the amp from a pawn shop. I dont know if it was the same socket, etc however as I never checked this.

I just had a resistor load plugged in when I tested it...so the real cabinet wasnt plugged in.

[John Phillips]

It's very hard to tell from that whether the tube just failed or whether something is causing it, although it does look it's just a dead tube that's the problem at the moment.

It's very important you check the speaker circuitry though, since an intermittent bad connection somewhere there will not only blow tubes, it will risk damaging the OT too.

[kingsxman]

THanks John. I will do that. I did put in a new speaker in my cab before the gig. Brand new so hopefully its not a problem.