Members bassthumpintwin Posted January 5, 2009 Members Share Posted January 5, 2009 Hey guys, Got another amp on the work bench. This time its a Vox AC-15 Tube Amp. Now, I really don't have any experience with tube amps directly, so this one has presented some extra learning curves. So here's what's goin on with it: There are two power tubes, and two preamp tubes. When you open up the amp from the back, you have the tubes in this configuration: Preamp1 Preamp2 Power1 Power2 The problem appears to be with Preamp tube number 2. Symptoms: When the amp warms up is becomes very noisy, even with nothing plugged into the input. That is a lot of crackling and popping, and even some humming. (Adjusting volume doesnt affect this either) The first preamp tube lights up, as do both power tubes, but the 2nd preamp tube barely lights up at all. There is just a VERY faint glow. The socket seems to be connected well to the the PCB and it's adjoining wires. There are no obviously damaged/bad components. I did notice that the power tubes have little flashes of blue light in them when they are warmed up. It's very faint, but noticeable. Is this normal? Well that's all I got in a nutshell. Any insight? Thanks guys, -Drew Link to comment Share on other sites More sharing options...
Members JeffBass Posted January 5, 2009 Members Share Posted January 5, 2009 Sounds like it's ready for Kindness's dumpster treatment. : O Link to comment Share on other sites More sharing options...
Members Guttermouth Posted January 6, 2009 Members Share Posted January 6, 2009 Hey guys, Got another amp on the work bench. This time its a Vox AC-15 Tube Amp. Now, I really don't have any experience with tube amps directly, so this one has presented some extra learning curves. So here's what's goin on with it: There are two power tubes, and two preamp tubes. When you open up the amp from the back, you have the tubes in this configuration: Preamp1 Preamp2 Power1 Power2 The problem appears to be with Preamp tube number 2. Symptoms: When the amp warms up is becomes very noisy, even with nothing plugged into the input. That is a lot of crackling and popping, and even some humming. (Adjusting volume doesnt affect this either) The first preamp tube lights up, as do both power tubes, but the 2nd preamp tube barely lights up at all. There is just a VERY faint glow. The socket seems to be connected well to the the PCB and it's adjoining wires. There are no obviously damaged/bad components. I did notice that the power tubes have little flashes of blue light in them when they are warmed up. It's very faint, but noticeable. Is this normal? Well that's all I got in a nutshell. Any insight? Thanks guys, -Drew have you tried replacing the preamp tube in question? crackling and /or popping usually boils down to: bad tube bad tube socket bad bad cap Link to comment Share on other sites More sharing options...
Moderators Kindness Posted January 6, 2009 Moderators Share Posted January 6, 2009 have you tried replacing the preamp tube in question? crackling and /or popping usually boils down to: bad tube bad tube socket bad bad cap +1 However, last time it was a dirty attenuator on the cabinet. Link to comment Share on other sites More sharing options...
Members PaulyWally Posted January 6, 2009 Members Share Posted January 6, 2009 However, last time it was a dirty attenuator on the cabinet. Sorry. Just had to laugh cause I know exactly what you must have went through before you figured that out... Link to comment Share on other sites More sharing options...
Members Guttermouth Posted January 6, 2009 Members Share Posted January 6, 2009 +1 However, last time it was a dirty attenuator on the cabinet. hehehehehehehe.... Link to comment Share on other sites More sharing options...
Moderators Kindness Posted January 6, 2009 Moderators Share Posted January 6, 2009 Sorry. Just had to laugh cause I know exactly what you must have went through before you figured that out... About two weeks of thinking "what the hell is going on?!?!" I mistakenly blamed some Monster cable speaker cables I thought were causing intermittent problems. I was skeptical of 5 different amps (they can't all be failing!), guitar cords, etc. I don't act until I know what's what, so it was mostly just nagging in the back of my mind. It is tough on a guy with OCD about his gear. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted January 6, 2009 Moderators Share Posted January 6, 2009 hehehehehehehe.... It probably got dirty spending a weekend at your house. Filthy hippy. :poke: Link to comment Share on other sites More sharing options...
Members bassthumpintwin Posted January 6, 2009 Author Members Share Posted January 6, 2009 have you tried replacing the preamp tube in question? crackling and /or popping usually boils down to: bad tube bad tube socket bad bad cap According to the guy I got the amp from, it's not the tubes. He claims to have tried multiple tubes to the same result. Link to comment Share on other sites More sharing options...
Members Guttermouth Posted January 6, 2009 Members Share Posted January 6, 2009 According to the guy I got the amp from, it's not the tubes. He claims to have tried multiple tubes to the same result. if he know so much about amps why didn't he fix it then ? :poke:seriously though, all voxes are good for is burning up tubes - change the tubes and see where you're at.you don't wanna troubleshoot it for a week and then figure out you had a shorted filament in a tube. next thing to do would be to start checking all the caps connected to the noisy tube socket.is this one of the newer pcb ac15's? Link to comment Share on other sites More sharing options...
Members bassthumpintwin Posted January 6, 2009 Author Members Share Posted January 6, 2009 if he know so much about amps why didn't he fix it then ? :poke: seriously though, all voxes are good for is burning up tubes - change the tubes and see where you're at.you don't wanna troubleshoot it for a week and then figure out you had a shorted filament in a tube. next thing to do would be to start checking all the caps connected to the noisy tube socket.is this one of the newer pcb ac15's? apparently he was "too busy" to "fix" it.... question: the two preamp tubes are not exactly the same, but I'm assuming they are compatible/equivalent tubes? that being said, can I switch the two tubes and see if the tube that works in the preamp 1 socket works in the preamp 2? I only ask, because I dont have any other spare tubes to test with at the moment. Link to comment Share on other sites More sharing options...
Members Guttermouth Posted January 6, 2009 Members Share Posted January 6, 2009 apparently he was "too busy" to "fix" it.... question: the two preamp tubes are not exactly the same, but I'm assuming they are compatible/equivalent tubes? that being said, can I switch the two tubes and see if the tube that works in the preamp 1 socket works in the preamp 2? I only ask, because I dont have any other spare tubes to test with at the moment. yes. you can swap the tubes and see if the problem follows the tube. Link to comment Share on other sites More sharing options...
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