Blew my amp, DAM

[gezza]

I posted this on amps,

But I hope it is ok to post here.

I had Triaixis running through my GT8 then into a Mesa Satellite 60watt.

So it like the second last song, I hear the splutter or farting noise.

I think, ah!! thats just a lead, you know.

Turned around to see a bright glow, then the pilot light went off. Amp Dead.

Then the gut wrenching electrical smell, you know you have fried something for sure.

I check the amp after the Gig, it blew the fuse.

But where did the smell come from.

When I got home I check the amp, 2 resistors burnt out. they were on the circuit board and had R110 and R111 beside them.

Now it's been a long time since I blew an amp up.

I am pretty sure a Power tube did this, as in the garage while tweaking my sounds, it made a horrible squeal. I looked at the back of the amp and one of the Power tubes was red hot. It did this twice in approx one week.

Man how are you supposed to see behind your amp, when you are singing and Shredding.

Stupid me, just dismissed it as one of those things.

Anyway off to the repair man.

Has this happened to anyone else???

Is this normal for a Power tube to do this???

Gezza

 

[disassembled]

Good maintenance practice for tube amps is to replace the power tubes if you are buying used and don't know how old the tubes are. Preamp tubes shape your tone but you are not going to cause as many problems as power tubes do so they aren't absolutely necessary as long as you like the tone.


Some recommend replacing the tubes once a year if you gig heavily and would probably prevent the failure you experienced.


Another point that you made about seeing the tubes redplate during practice and making all kinds of noises should have threw up some flags for you and this probably could have been prevented. I hope the only problem with the amp are those 2 resistors.

Good luck.

Greg

 

[rpdz]

That sucks. I'm sorry to hear that. I hope you have a good tech in the area. They are hard to come by around here. In the future you may want to invest in a stereo power amp like the 2:90. If one channel goes, you can finish the gig with the other one.

 

[gezza]

Hi all,

I sent a email to Mesa with some pic's.

They replied very fast, same day.

I also asked what is the Bias Range. It is very low.

I thought 35 was cold and 50 was hot.

Here is the reply.

Sounds like you burnt up the screen resistors due to a failed power
tube...this is fairly common in tube amps. If you're lucky the fuse
should catch something like this before the screen resistors smoke.
However if the fuse takes too long to blow the screen resistors take all
the damage.

Bias ranges vary, but should be somewhere in the range of 20-30
Milliamps. Have your tech look at it. Replacing the screen resistors
should get it up and running. Please realize that you should also
change the 6L6's before firing the amp back up so this doesn't happen
again.

Best Regards,

It get repaired next week.

Thanks

Gezza

 

[disassembled]

35 and 50 mean nothing without knowing the plate voltage and max. tube dissapation.

Once you know all of the numbers then you can calculate the max current range for tubes. The higher you run the current the quicker your tubes will wear out/fail.



Greg