Hey guys,
I just got my Mark IV the other day and after going through it, I have a couple of questions for the gurus.
1. The reverb is not working. I pulled the preamp tubes to make notes of what were installed, and I noticed that one of the previous owner had put an 12AX7 in the reverb slot (#4) and a 12AT7 in the input stage slot (#1). Swapping these didn't fix the reverb. The amp still works, so I'm assuming that the 12AT7 is fine. I've looked into all the simple causes I could think of. The cables are plugged into the chassis and the tank, the reverb knob is turned up to 10, etc.. Any idea of things I could try?
2. There is a mystery input jack on the bottom of the chassis. It's located just below the eq rocker switch. I'm not talking about the footswitch remote jack, this is a 1/4" jack. No label that I can see. Any other Mark IV ver. a owners know what this is for? Is this a standard jack, or some mod? My first thought was that it's a pedal input for the reverb, but I haven't explored that theory yet.
3. There is a quiet fuzz sound that accompanies the low notes of the guitar. This is mainly noticeable with a clean setting. It's tolerable and you'd never hear it at stage volumes, but it is bugging me. I've looked for anything in the back of the amp that could be vibrating, but no luck. Any ideas what could be causing this?
Sorry for the novel, and thanks in advance for any help.
I just got my Mark IV the other day and after going through it, I have a couple of questions for the gurus.
1. The reverb is not working. I pulled the preamp tubes to make notes of what were installed, and I noticed that one of the previous owner had put an 12AX7 in the reverb slot (#4) and a 12AT7 in the input stage slot (#1). Swapping these didn't fix the reverb. The amp still works, so I'm assuming that the 12AT7 is fine. I've looked into all the simple causes I could think of. The cables are plugged into the chassis and the tank, the reverb knob is turned up to 10, etc.. Any idea of things I could try?
2. There is a mystery input jack on the bottom of the chassis. It's located just below the eq rocker switch. I'm not talking about the footswitch remote jack, this is a 1/4" jack. No label that I can see. Any other Mark IV ver. a owners know what this is for? Is this a standard jack, or some mod? My first thought was that it's a pedal input for the reverb, but I haven't explored that theory yet.
3. There is a quiet fuzz sound that accompanies the low notes of the guitar. This is mainly noticeable with a clean setting. It's tolerable and you'd never hear it at stage volumes, but it is bugging me. I've looked for anything in the back of the amp that could be vibrating, but no luck. Any ideas what could be causing this?
Sorry for the novel, and thanks in advance for any help.