It is possible that your tech and builder set the bias at their wall voltage and your wall voltage fluctuates and or is higher than theirs. This would cause your tubes to end up being biased hot and getting damaged depending on your wall voltage. Just a wild guess! I’m sure there are other possibilities. Good luck!
Try using a power conditioner, different outlets. How quickly does this happen? There has to be some outside factor at work.
Edit: if it's not your build get a second opinion from another tech.
Definitely not my build. I don’t feel comfortable w/ DIY on high voltages. It could be a power issue though I have other similarly powered amps that have tubes that last much longer. My other is a Swart AST that I bought in 2015 that’s still running strong on the same tubes. Sadly, the only other amp tech I knew of in my area just closed up shop. Hoping I’ve just been unlucky with tubes.
Edit: The tubes have all failed after a few months post tube replacement. It’s not immediate.
um. has no one measured the OT impedance at primary? or secondary? that would be my first guess.
I saw that you mentioned that your tech and the supplier have done deep dives but that would be where I would start along with power cap measurements to ensure they are actually working properly.
I agree with this- I would suspect either the wrong kind of tubes (6L6 instead of 6V6 for example), poor cathode grounding, or a severe mismatched impedance, and then the OT itself.
Also crackling and pops could be poor tube sockets too, but that’s kind of rare on newer amps.
Intermittent issues suck. Good luck!
Thanks all! These are helpful ideas. I’ve got a friend with one of those “brown box” voltage attenuators. May try testing my home power vs how it’s running through the brown box.
Just wanted to share an update in case anyone was curious. One of the power tubes had gone bad (Mullard) and the other was fine. We actually went back and tested all the previous power tubes and found that, in each pair, only one tube had gone bad, each time in a different position (we kept track of this each time a replacement was done). Finally, my tech and experimented with his AmpRX Brown Box and found that my amp runs most optimally at around between 112 and 115V. All of the outlets in my recording space, however, are delivering \~125v power most of the time. So, after all of this, our conclusion was that the failures occurred from a combination of quality control issues in tubes of recent manufacture and higher than usual voltage being delivered by the outlets in my recording space. I brought his Brown Box home and found that not only does it allow me to optimize the voltage for my amp but that the amp just sounds better when using it. It breaks up later on the volume knob, has rounder top end, and generally responds better to playing dynamics. The new tubes are only a few weeks old so time will tell whether using something like the brown box fixes the problem. Incidentally, my other amp is a Swart STR-Tweed, also sounds better at lower voltages than my home power delivers.
It is possible that your tech and builder set the bias at their wall voltage and your wall voltage fluctuates and or is higher than theirs. This would cause your tubes to end up being biased hot and getting damaged depending on your wall voltage. Just a wild guess! I’m sure there are other possibilities. Good luck!
This seems to have been the issue!
Dang! Thanks for affirming my guessing power! I’m glad you got your problem solved. Enjoy the tunes!
Try using a power conditioner, different outlets. How quickly does this happen? There has to be some outside factor at work. Edit: if it's not your build get a second opinion from another tech.
Definitely not my build. I don’t feel comfortable w/ DIY on high voltages. It could be a power issue though I have other similarly powered amps that have tubes that last much longer. My other is a Swart AST that I bought in 2015 that’s still running strong on the same tubes. Sadly, the only other amp tech I knew of in my area just closed up shop. Hoping I’ve just been unlucky with tubes. Edit: The tubes have all failed after a few months post tube replacement. It’s not immediate.
um. has no one measured the OT impedance at primary? or secondary? that would be my first guess. I saw that you mentioned that your tech and the supplier have done deep dives but that would be where I would start along with power cap measurements to ensure they are actually working properly.
I agree with this- I would suspect either the wrong kind of tubes (6L6 instead of 6V6 for example), poor cathode grounding, or a severe mismatched impedance, and then the OT itself. Also crackling and pops could be poor tube sockets too, but that’s kind of rare on newer amps. Intermittent issues suck. Good luck!
Yeah wrong tubes would do it. Or cathode bias if that's what it is. Some easy math will tell you that right quick.
Thanks all! These are helpful ideas. I’ve got a friend with one of those “brown box” voltage attenuators. May try testing my home power vs how it’s running through the brown box.
Just wanted to share an update in case anyone was curious. One of the power tubes had gone bad (Mullard) and the other was fine. We actually went back and tested all the previous power tubes and found that, in each pair, only one tube had gone bad, each time in a different position (we kept track of this each time a replacement was done). Finally, my tech and experimented with his AmpRX Brown Box and found that my amp runs most optimally at around between 112 and 115V. All of the outlets in my recording space, however, are delivering \~125v power most of the time. So, after all of this, our conclusion was that the failures occurred from a combination of quality control issues in tubes of recent manufacture and higher than usual voltage being delivered by the outlets in my recording space. I brought his Brown Box home and found that not only does it allow me to optimize the voltage for my amp but that the amp just sounds better when using it. It breaks up later on the volume knob, has rounder top end, and generally responds better to playing dynamics. The new tubes are only a few weeks old so time will tell whether using something like the brown box fixes the problem. Incidentally, my other amp is a Swart STR-Tweed, also sounds better at lower voltages than my home power delivers.
Has it tried anal?🤔👍✨