Tube power amp troubleshooting

[Inazone]

A few months back, I accidentally plugged in my Carvin T100 power amp without a speaker load on one side while it was set for stereo operation. One of the EL34s on that side (there are two per channel) blew. I replaced both Channel B EH EL34s with Groove Tubes EL34s, played through that side just to confirm that it was working again, and then didn't use it again for months...until yesterday.

It now sounds as if Channel B is clipping a LOT when I play with distortion. I don't notice it when playing clean, but with distortion it sounds weak and then clips/cuts out. I confirmed that it wasn't a problem with my preamp, cab or cables, as switching the preamp and cab to Channel A sounds just fine and connecting another preamp and cab to Channel B continues to sound like ass. Is this likely because I didn't bias the amp after installing the new tubes, or the sign of something more serious? I don't know the first thing about tube amp biasing, as all of my previous tube amps have been fixed-bias and I always replaced the old tubes with identical replacements.

[Twisteramps]

Swap the tubes, see if the problem follows the tubes. Also, did you swap out or check the 12ax7s in the power amp - could have fried one of those too.

Pete

[Inazone]

Nope, didn't swap out the 12AX7s. I may just have this serviced now to save myself any future headaches, as I intend to record with it. Are there any concrete guidelines on how often the preamp and power tubes ought to be changed in a power amp?

[Twisteramps]

Nope, didn't swap out the 12AX7s. I may just have this serviced now to save myself any future headaches, as I intend to record with it. Are there any concrete guidelines on how often the preamp and power tubes ought to be changed in a power amp?

Depends on how loud and how often your amp is run, and also how hard it on tubes - higher plate voltages and bias settings will burn tubes out quicker. One thing I'd advise is to keep a fresh set of *all* tubes used in the amp for troubleshooting purposes and for spares. Every 6 months or so (again, depends on how loud and often you play - If you're doing a few hours a day and your amp never gets moved, yearly might work: If you're gigging every weekend and your amp gets moved around a lot, I'd go at least every 6 months) I'd swap out the power tubes at least and see if it makes a difference in volume and tone. If not, put the old ones back in and wait another 6 months.

Pete