Mark IV replacing volume knob - Possible to do at home?

[j0l]

I have managed to sausage finger the push/pull knob of my lovely Mark IV Mesa Boogie. (well the boot of my car did) & have sourced the replacement pot from Mesa themselves.

Is this the kind of repair that I can do simply at home? It looks like there are two points to solder. If so any tips on dis-assembling?

I'm not mechanically too bad, and I'd like to think I know when to stop but is this straightforward? I'm not great at soldering but with some patience and my reading glasses on I can probably do this.

Thanks

Jol

 

[dtrax]

Replacing a pot is simple. Just note which wires connect to the input, wiper and ground lugs and you're good to go.

BUT, tube amps are high voltage devices and can hold a charge (somewhere in the range of 450VDC) after they're powered off. In an amp like a MarkIV, there are bleed resistors that will dissipate this voltage and will normally be safe to work on the circuit within a minute or two. However, you should never blindly trust that bleed resistors are working as intended; you must confirm voltage has dropped to safe level (personally i shoot for under 10VDC). Personally I just use a 1K 10W resistor and it drains the caps in seconds, as would any tech. And it should probably go without saying, but absolutely make sure the amp is disconnected from mains power.

For your safety, it's probably best to have a tech do it.

 

[dradrachirgnildoc]

Should be an easy fix as long as you're careful with the HV inside the amp being absolutely safe.

I have broken most of the push-pull pots on my Mark IV and fixed them in a variety of ways (disabled the Pull Silent on the Master Volume control, hard-wired the Lead Fat ON as the knock that broke that pot shaft annihilated the switch).

Some of them are awkward to get at, due to how much stuff is crammed into the chassis.

 

[robredo_mattila]

Should be an easy fix as long as you're careful with the HV inside the amp being absolutely safe.

I have broken most of the push-pull pots on my Mark IV and fixed them in a variety of ways (disabled the Pull Silent on the Master Volume control, hard-wired the Lead Fat ON as the knock that broke that pot shaft annihilated the switch).

Some of them are awkward to get at, due to how much stuff is crammed into the chassis.

Hi there, do you have a diagram or any instructions regarding how to disable the Pull Silent on the master volume? I am replacing the Master Volume (potentiometer is faulty) and am considering forgoing the pull silent feature.

Thanks

 

[dradrachirgnildoc]

Hi there, do you have a diagram or any instructions regarding how to disable the Pull Silent on the master volume? I am replacing the Master Volume (potentiometer is faulty) and am considering forgoing the pull silent feature.

Thanks

Hi, I didn't do the Master Vol repair on my amp but I did do basically the same with the Lead Fat control (to be Always On).

Basically the existing control will have 5 wires come off it, three for the usual pot controls and two for the switch. swap the three pot controls to the new Master Volume control and keep the two switch wires separate. I'd imagine that for usual operation the switch will be open (wires not connected) and for the Pull Silent the switch will be closed (wires connected). wire the new pot and keep the switch wires separate, then touch the bare ends together to see what the effect is, then wither solder the wires together to have an Always On result, or (as I suspect) keep them apart but tape the ends so that the switch is open, for normal operation.

Hope that helps!