The 2 most common causes of crackling noises are pre-amp tubes or old failing resistors, since you bought the amp used, theirs a pretty good chance the pre-amp tubes are the original factory tubes and are getting tired, if you know a good tech or shop it wouldn't be a bad idea to take it in and have all the tubes replaced and the bias checked on the power tubes, I didn't say it would be cheap but some new tubes would probably make it sound like a new amp and if you did happen to have a bad resistor the tech could take care of that too, now if that's not the way you to go, here's the alternate plan, go buy a couple of new pre-amp tubes, it's always a good idea to have a few spares anyhow if you own a tube amp, unplug the amp,let it cool down, in the back of the amp on the right hand side you'll see the pre-amp tubes, small tubes that will probably be marked 12ax7 or STR 7025, their will be several of these, starting with the one on the farthest right, grab the old tube and slowly work it out, pulling down and working it in a small circular motion, it's a good idea to use a cloth to grasp the tube with when you are doing this, take a new tube, look at the pins, should be 9 pins with a large gap, look at the socket you are going to put it in, make sure you line up the pins with the socket, make sure the tube is seated good, then turn on the amp and let it warm up, if it doesn't crackle then you found the bad tube, if it still crackles, turn it off and unplug the amp again, take the new tube out, and replace it with the old tube and repeat the process on down the line with all the pre-amp tubes, if it's a pre-amp tube making the noise you find it, the last tube before the power tubes will probably be a 12AT7, thats the phase inverter tube, that's where you stop the tube swapping, if it's still noisy, take it to a shop! Don't even think about taking the chassis out of the cabinet to have a look, tube amps store high voltage and can do you serious harm. Pre-amp tubes are the cause of alot of the noise in tube amps, new, quality tubes usally will clean up a noisy amp.... Keep us informed on how things turn out, if you have any questions, just ask...........Correction to the above, your amp does not use a 12AT7 for the phase inverter tube, it uses a 12AX7, so your first 2 tubes will be your pre-amp tubes..........

[Edited by pstring on 08-18-2003 at 10:14 AM]