If all other options have been checked a bad solder point seems like a likely culprit. Also the faulty piece of gear that works fine in the shop is pretty standard I've been through that before!
Is My Tube Amp Unfixable? Help Needed
Hi All: It's been a while since I have posted, but I am posting now because I need advice from those who may have experienced something similar. I really am in a tough spot with a tube amp that it pains me to say I am tempted to literally throw away or give away. This is a long story, so grab a beer or cup of coffee:
In October 2020, I bought brand new Quicksilver Mono 120s...FANTASTIC sounding amps, btw, and the third pair of Quicksilver monos I've owned (I also own their line stage preamp). Immediately, the left channel amp began emitting static pops and crackly, intermittent noise...low level but loud enough to hear from my listening position 8 ft. away. After painstakingly exhausting every possible source of noise (power tubes, driver tubes, speaker, preamp, interconnects, iPhone, CD player, electrical socket, power cords, etc), I called Quicksilver and was told to send the amp back...could be a bad resistor but now sure. Quicksilver looked it over and determined that it was working perfectly...no noise. I got it back 3 weeks later and...same exact noise. Several months later, I called QS and explained the situation in detail. They said to send it back a second time with the tubes I was using. Again, I shipped it back, and Mike Sanders did a very, very thorough check of the amp. He called me to discuss, and the verdict was the amp was exhibiting no noise and working perfectly. I got it back and yep...the same noise with the same exact tubes Mike had. In addition, UPS had dropped the box so hard in transit that when I received it from QS, 2 of the 3 binding posts has completely sheared off and were rattling in the box.
So now I had a noisy amp the manufacturer could not diagnose and that was unusable. I was not going to send it back to QS a third time ($100 in shipping a pop), but I needed the binding posts repaired. So I drove it an hour to a local tube repair shop that specialized mainly in guitar amps but who told me he could work on it. And yes, you guessed it..."Your amp is working fine. We checked it out top to bottom, and no noise." $160 later for repaired binding posts, this amp is STILL noisy and actually worse than ever. Btw, I have since moved to another state and set the amp up in a completely new place...same noise.
So, I have a $2,000 amp that I cannot use and apparently no one can repair, and I am at my wits end. Btw, the amp is still under warranty, but QS no longer makes the Mono 120s, so they cannot swap it out for a new one. Do I simply just keep shipping this amp to random repair shops only to hear "it's working fine," or do I literally throw it away? Audiogon, I need your advice.
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- 41 posts total
@bojack Don't panic! This is solvable. The first thing to do in a situation like this is move the monoblock to the other channel and see if it does it there. Apparently the other monoblock is fine, right? If its quiet in the other location, then its a pretty good bet that something about this amp is more sensitive than others to noise that is present at the first location, like a digital device such as a wifi router, DAC and so on. In any event this sounds like an RFI issue, which might also be caused by an oscillation in the amplifier itself. It might be just on the edge of oscillation and so behaves in other locations. Hypothesis of course. So if the amp still makes the noise in the other channel, then what you do is remove the input tube (while the amp is off of course). It should not damage the amp to run it without this tube. The question is, is the noise still there? If not then we have a very good idea of what circuit is causing the noise! If the noise is still there, then the 2nd (driver) tube can be removed. The driver is capacitor coupled to the output section so this can be done without damage, but again the amp must be off when this is done. One possible way the amp can make this noise is if a certain part was omitted, called a 'stopping resistor'. It sits (or should) at the input of each tube in the amp. If not there, the tube can go into oscillation. Often people get away with not installing these resistors in their DIY project, but they are good practice. But if the amp is handwired, its the sort of thing that would be easy to forget on accident and might be really tricky to figure out later since the amp might behave, although not all the time. Try these tests and get back to us.
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- 41 posts total