A little over a year ago, or was it two, I bought a Nobsound tube amp. The amp is a type A and operates in the ultra linear mode. It uses 1 5U4C Russian rectifier tube, two Chinese 6N9P tubes and two EL34B tubes. I don't kinow if they are Russian or Chinese. When I first powered it up everything went smoothly but after maybe an hour or so it made this loud static like noise. I promptly turned it off. Deciphering the directions I realized the amp was made to operate on
110 volts, not the 125 typical in my house. Oops. So I wired up a transformer in buck configuration to get 110 volts and tried the amp again. And it has operated fine since. Until a few days ago. Once again the loud static noise. Changing the volume changed nothing and I shut the amp off. After it cooled I pulled each tube out and then re-inserted it thinking that maybe a bad connection may have been the problem. After again powering the amp up it is once again performing flawlessly. So what gives? I have read about red plating, how it damages tubes pretty fast, and am thinking that maybe I damaged the tubes running them at the too high voltage for a while. But why does the amp sound great after it has a chance to cool off? Since the latest incident I have run the amp for about 4 hours straight so I don't think the problem is heat related. I mean just because the amp is hot it doesn't necessarily mean it is going to act up. Both times the amp made this noise it was getting its input from a built in bluetooth reciever. I thought this might be the problem but since the noise is volume control insensitive it seems to me that the problem is probably unrelated to the input. The noise is LOUD too. I mean hurt your ears loud. I never turn the volume up as loud as the static noise was. When I say static I mean scratchy crackling noises, not white noise. Kinda like if someone was dragging one wire across another. Unfortunately I could not tell if the noise was coming from both speakers. I just ran over and turned it off the first time it happened. The second time I tried turning down the volume and then turned it off. Should I be shopping for tubes? And could it be any of the tubes? There are no tube testers local to me. The closest I know of is an hour and a half drive away. Thanks, Eric- posted
4 years ago