I own a Crate VC5115 guitar amp and like almost all owners of the amp I have experienced the problem that all vintage club owners have with the clean channel. While the drive channel works perfectly fine, the clean channel has random spikes in gain and volume. I would be playing on the clean channel and suddenly the amp would get extremely loud.
Well, I researched the problem online and found that many people also had this problem and most people said that it was because the signal path went through all three of the input jacks and that if one of them was oxidized it would mess up the others. So I bought deoxit in the hopes that this would solve my problem and it did not. I have read many ideas on what could be the problem and nothing would fix it so I finally decided to take the amp apart and have a look. So, for any owner of a Crate VC amp having the Clean channel problem, plz do not get rid of this wonderful, great sounding tube amp because I am going to tell you the problem and how to fix it.
First, if you have never worked on a tube amp plz do not do so if you do not know how to discharge the capacitors. Try to find someone who knows how to do this if you can.
WARNING!! Tube amps hold voltage sometimes even months after being unplugged and turned off. This voltage can be deadly, so work at your own risk and never put two hands inside of the amp at the same time. Keep one behind your back to keep the voltage from running through your body constantly.
You can look on youtube for videos that show you how to discharge the voltage from a tube amp if you want to do this yourself.
Alright, the problem is simply a blown capacitor. Mine was the biggest one on the board and my dad, who used to be an electrician, noticed it was blown as soon as he looked at the board. So, take the screws out of the back of the amp and remove the back cover. Then examine the capacitors, which are the large cylinders on the circuit board. DO NOT TOUCH ANYTHING! (If you really can't find information on discharging capacitors I will make a video tutorial, just let me know in the comments section.) Ok well, the blown capacitor should be blue, or atleast mine was, and the top of the capacitor should have a bubble. The blown capacitor will have a bubble at the top of the cylinder. Once you identify te capacitor that is blown you will have to go on ebay and purchase a new one. Mine was a 16000 uf 12V capacitor I believe which I got on ebay for $8. Long story short, you need to remove the blown capacitor (after discharging the voltage) and solder the new one on.
Soldering on a circuit board requires a special soldering iron that sucks the solder off of the old capacitor before you can remove it. Be very careful and try to find someone who has experience soldering circuit boards.
If you have any questions or would like more information I could make a video tutorial and show you more indepth. Leave your comments and let me know if this helps anyone out.
