Guitar Gear Forum

So I’m trying to get my mark IV converted to US voltage. The export model schematic does show the OT as having. 117V tap. Last week while I was inquiring support about something else I sent said schematic and asked for confirmation. She confirmed that that was correct and informed me that the varistor and fuse needed to be changed. I requested part numbers but wasn’t hearing back so I tried starting a new support email. This second person comes back and tells me that the schematic and the other person are wrong and I’ll need a new transformer. He gives me all the part numbers. Since things are inconsistent I work out with my tech that I’ll order the parts needed in case it does have the proper tap and we can just get it switches asap. Annoying but fingers crossed (worst case scenario said transformer is only $280 which isn’t as bad as I thought)

Well the first person just emails me back again with part numbers. Except she says it’s a 4A fuse. The other guy told me 3A and that’s what I ordered. I do think I have some 4A lying around but wtf man

So not really sure what to do or think about the fuses but at least there will be some clarity when the parts come and I take it in

That's kind of annoying. Especially since you're taking what they are saying as essentially gospel, only to get mixed messaging from two customer support representatives.

with fuses, you can't go higher since it potentially allows more amperage than the amp can handle, but lower is fine so go 3A

Guitarbilly wrote: ↑Wed May 29, 2024 12:35 am with fuses, you can't go higher since it potentially allows more amperage than the amp can handle, but lower is fine so go 3A

This. Higher than spec could cause the amp to get subjected to conditions that would be detrimental to the PCB and other components. 3A is likely the best way to go.

Didn’t know that, thanks for the tip

This is not surprising from Mesa, considering their schematics are basically inaccurate children's drawings of some potential version of their amps lolol.

ninjaraf wrote: ↑Wed May 29, 2024 11:32 am This is not surprising from Mesa, considering their schematics are basically inaccurate children's drawings of some potential version of their amps lolol.

There is a good reason that techs cry when someone brings a mrak in

that said, there isn't a great deal for a competent tech to worry about here. Pop it open, it either has the right primary taps bundled away somewhere or it doesn't. If it does, then swap over to the right tap and test the voltages. The MOV isn't that important - most amps don't have them and Mesa doesn't do the best implementation anyway.

This article by RG Keen shows how it should be done and how to select the right MOV: https://www.premierguitar.com/the-immor ... -mods-pt-3

A 3 or 4A fuse will be fine. They are blunt tools in this application. If it fires up and doesn't blow a 3A fuse then use that. The conventional wisdom is that doubling the voltage halves the current, so stepping from 230 to 117 would double the current => 1.5x2 = 3A

For comparison a 120V Laney GH100L uses a 5A primary fuse. A 5150iii 100W at 115V uses 6A.

ninjaraf wrote: ↑Wed May 29, 2024 11:32 am This is not surprising from Mesa, considering their schematics are basically inaccurate children's drawings of some potential version of their amps lolol.

Mesa doesn't keep great records of what their amps are at any given point. Just watch the video where Steve Fryette discusses the Synergy IICP module with Paul Hennig.