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.

bojack

Hi Larry,

Thanks for your suggestions, but the amp exhibits noise with no preamp interconnect attached...just the amp and speaker load. And it does this attached to multiple AC outlets in different states! Additionally replacing the noisy amp with another QS Mono 120 in the same position (same everything else) results in a perfectly quiet amp. It is 100% the amp itself (a component, transformer, etc). 

Wow.

If it is under warrantee can you get your money back? I mean they can’t fix it. Take a video of it not being connected and the sound it is making for proof.

Yep, did that as well. Sent QS a video of the amp making the noise that was very clearly audible. I offered the same same file to the second repair shop but was told he did not need to see it because "the scope would catch anything wrong." Btw, my speakers are 89dB sensitive (Spendor 1/2s), so it's not like I have crazy sensitive horns, etc. 

Have you tried tightening the sockets for the left channel?  It could be a loose or bad socket causing that kind of noise.  If you are handy, you can try reflowing solder joints for the left channel.  A friend hunts down noise by touching joints with a pencil eraser to see which joints are noisy.  This is something one has to take extreme care when doing this because the amp is on and connected to speakers.

Hi Larry,

My very first guess was also a bad solder joint somewhere, but Mike personally went though the amp and could not locate any. And the binding posts have always been fine to my knowledge...nice and tight. The guitar amp shop actually did a very nice job on the new posts (proper soldering using new QS posts). I actually suspect that it might be a bad output transformer, but that is a crazy guess. I am not an EE, so I am relying on others to actually find the issue. I'm not about to reflow any joints myself because I would very likely introduce a new problem.