Bojack if the noise is gone without the 12au7 that tube probably has a dirty tube pin that can cause serious noise.
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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Again, waiting for Ralph. But along the lines of @jond's train of thought, I've had more than one tube which did not function correctly, and I VERY slightly and gently bend the pins one way and the other to ensure a solid contact, and it worked every time. Also, with a light gauge sandpaper gave the pins a couple of swipes. Wiped them clean and voila. |
@bojack Good work. Now we know the problem is associated with the input section. The big filter caps are likely off the hook. A loose connection is entirely possible so that should not be ignored. If this amp is handwired (and as best I can make out, it is) then the thing to ask a local tech to look for is stopping resistors on each section of the socket of that 12AU7 (pins 2 and 7, for those keeping track). Loose solderjoints could also be an issue. But I doubt that on account of the amp has done some traveling so that should have shown up, but intermittents being the way they are, the are far more likely to show up in the customer's home than on the bench. If you can remove the bottom cover of both amps and place them side by side with the bottom facing you, the good amp can be a map of what the bad amp should look like inside. So you can look for differences between the two channels on that 12AU7 socket. You don't need to poke about the amp- this is just observing what is there. |
- 41 posts total