Search results

The power amp stabilization modification fixed the problem. I got some 2.2k 1W resistors and was able to solder them in place, now I can crank it with no more crackling. Thanks so much for your response and posting the schematic!

That's really helpful! The schematic I found already showed the 2.2kΩ installed. The power amp schematic on page 41 in the document you provided does not have the control grid resistors. The input signal connects directly to the control grid. This might just be what I need. I'll take a look...

Very possible. I found a Mark IV schematic, and their really isn't much to the tube circuitry that is isolated to the two inner-most power tubes: 2.2kΩ control grip resistors 220kΩ bias resistors 470Ω screen grid resistors I'll see if I can get in there with an ohmmeter and verify the resistor...

I did some additional testing, including the conditions you suggested. No difference--the crackle is still there: 1. Different input cable 2. Different speaker cable 3. Different speaker cabinet 4. Different speaker output

Hello, Everyone, My Mesa Boogie Mark IV Rev A is crackling at higher volumes (higher being greater than 1) when in SimulClass mode. The crackling can be heard in the video below. Does anyone have any idea what the cause of this is? Analysis: 1. The crackling almost sounds like static. 2. The...

Hello, Everyone, I'm restoring a Mesa Boogie Mark IV Rev A, wired by Kaydee in June 1992. For the preamp tubes, there is one 12at7 tube, three 12ax7 preamp tubes, and one that is completely unmarked. Questions: 1. Could someone please confirm that the unmarked tube should be a 12ax7? 2. Is...