Bass 400+ tubes getting hot + blowing fuse

[kozmikb]

Bass 400+ with Mesa 6L6GC STR430 tubes into an SWR Goliath 4x10 and an SWR Goliath II 4x10. I can be 2 or 3 songs into a set and my output will slowly disappear as two or more tubes start glowing somewhat. If I don't quickly switch the standby off the 8-amp slo-blo fuse will blow. I can leave it on standby for a couple of minutes, turn it back on and it may work the rest of the night. One of the power tubes had a large black spot in it. I replaced it with all I had which was a Mesa 6L6GC STR420 from my old Strategy 400. Still, two or more seemingly random tubes will start glowing and the problem repeats. This doesn't happen every set and sometimes won't happen the whole night! Any ideas on what's causing this?

Thanks for anyone's help.

Have a good one.
koz

 

[mesa115]

I have had similar problems with a Boogie Nomad. I had a 400+ and it did not do what you are describing but the Nomad did.

1st, when it happens again, look to see if 1 or 2 tubes are glowing brighter than the others. One will be much brighter, the other just a little.

Then look at your owners manual and find out which tubes need to be matched. If you are lucky it will be the two that are glowing the most, but if not, you may need to replace 4 tubes.

2nd, do you experience any hiss, ringing or feedback? If so, you may have a bad pre-amp tube, but this is unlikely. I can almost guarantee that replaceing two or at most 4 power tubes will completely solve this.

If you want to be sure, call mesa on their 800# tell them exactly what you told the forum, and they may tell you what pair of tubes is most likely the culprit, but black spots on tubes always means it it shot, and volume fading is always a power tube problem.

 

[Guitarzan]

+1 to above.

 

[kozmikb]

thanks


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