Amp MV pot replacement.

[Findthetone1]

Quick question for you DIY amp experts. I need to replace the MV pots in my amp. They are not PCB mounted. Do I need to worry about bleeding the caps? I 've been in amps before and I know not to go sticking my fingers in places willy nilly but I want to double check.

 

[sahlomonic]

YES. Anytime you're working 'under the hood', always discharge the caps. Never know if you'll accidentally touch something you're not supposed to.

If you're unsure how, there are a plethora of YT vids that can guide you. I always start with striking a nice open chord with the amp on, then flip the power switch off and start chugging away as the sound dies off. Then put a big resistor (I have a 'discharge wire' made up with alligator clips but forget the value of the resistor) between ground and the filter caps to quickly discharge them, then confirm with a multimeter.

I'm sure you could get away with replacing the pot w/o discharging the caps, but I always err on the side of caution.

If it's a low watt (20w or so) amp, they tend to discharge pretty much instantly when powered off.

I'm no pro, but that's the system I follow. Someone with more good edumacation than me please chime in

 

[Chubbs]

What amp is it? Some automatically discharge and others do not. Still check though. Fwiw, my process is check the filter caps with a multimeter, then various points on the board, then around the area I'm working on. Also, if it's Marshall don't forget the cap under the board.

 

[HarryCooter]

I've never opened my MV up, but since it's a modern amp I'm pretty sure there are bleed-off resistors. With that said, you should always discharge the filter caps. I would recommend watching a Youtube video on it so you can see what to do rather than be told. I also recommend an alligator clip and resistor as suggested above. Also, why are you having to replace pots in a MV? EDIT: I'm an idiot. I read Mark V, not master volume.

 

[Findthetone1]

What amp is it? Some automatically discharge and others do not. Still check though. Fwiw, my process is check the filter caps with a multimeter, then various points on the board, then around the area I'm working on. Also, if it's Marshall don't forget the cap under the board.

It's a SLO30. It's from the run that has the linear MV pots and I want to change them to audio. I have no interest in sending it all the way to BAD to have them do it as I bought it used and deal with shipping companies every day. I'd like to keep my amp in one piece

 

[Chubbs]

It's a SLO30. It's from the run that has the linear MV pots and I want to change them to audio. I have no interest in sending it all the way to BAD to have them do it as I bought it used and deal with shipping companies every day. I'd like to keep my amp in one piece

I'd get some other input as well but I would go amp on, then into standby, then amp off then check voltages across the board from the top, then check voltages on the pots. Then work with one hand if possible just in case.

 

[Findthetone1]

I'd get some other input as well but I would go amp on, then into standby, then amp off then check voltages across the board from the top, then check voltages on the pots. Then work with one hand if possible just in case.

OK. Thanks

 

[PatF]

A common value for the resistor is 10K 2 Watt. Solder 6-8" of wire and an insulated (rubber boot) alligator clip to both sides and heat shrink the resistor. 22, 20, or 18 AWG wire is fine.

Clip it to a bare metal spot on the chassis or a ground lug and then somewhere on the power rail. Pin 1 or 6 of a 12A_7 tube or positive side of a filter cap. Probably best to go to as close to the 1st preamp tube/cap as possible.

 

[Findthetone1]

A common value for the resistor is 10K 2 Watt. Solder 6-8" of wire and an insulated (rubber boot) alligator clip to both sides and heat shrink the resistor. 22, 20, or 18 AWG wire is fine.

Clip it to a bare metal spot on the chassis or a ground lug and then somewhere on the power rail. Pin 1 or 6 of a 12A_7 tube or positive side of a filter cap. Probably best to go to as close to the 1st preamp tube/cap as possible.

Thanks! I didn't realize amp volume pots can carry a lot of voltage. Used to guitar pots I guess.
I appreciate everybody's help!

 

[SpiderWars]

I always start with striking a nice open chord with the amp on, then flip the power switch off and start chugging away as the sound dies off.

That should get most of it. The remaining should be so low that I wouldn't worry about it. Just check it to be sure.

 

[Findthetone1]

That should get most of it. The remaining should be so low that I wouldn't worry about it. Just check it to be sure.

Thanks. Maybe I'll skip checking it and get some of this action