Marshall JTM 30 conversion to 110 volts from 230 volts

[misterc57]

I just purchased a JTM 30 that came from overseas and is setup for European usage.

I would like to mod it to run on USA 110 volts.

I am wondering what I am in for. I am hoping I can just change some connections on the power transformer and change the main fuse.

I do not know if the power transformer is setup for both 230 and 110 volts.

Would I need to change anything else like the power switch?

Thank you! Mark

[oc disorder]

Hi Mark
The power switch is ok if it can handle 230v it can certainly manage 120 !
The other way round (U.S. one in Europe) the switch would have to be able to handle 230.
Some wires will have to be moved on the primary of the power transformer.
The fuse is the only other thing you will have to change.
The existing 1 amp has to be changed to a 2 amp.
I'm attaching some diagrams.
Basically there are 2 120 volt windings.
For 240 they have to be in series ie one connects through another.
For 120v they have to be in parallel ..windings in the same orientation.
So you pull out the link in the middle and connect the now free side to its
corresponding wire in both cases. see diagrams.
If you are at all unsure remove the chassis and take it along with the diagrams to a tech. Even an electrician could figure that out although he may need a suitable soldering iron.
Also see this related post http://music-electronics-forum.com/t19274/
Booj has a neat drawing.

[misterc57]

worked great

thanks!!!

[Chris Bailey]

Hey oc disorder. I got a jtm30 that was Katrina and the Waves stage and studio amp from Nottingham UK and I'm in the US. I can't read the drawings you posted. Can you help me out? Thanks Chris

[Jon Snell]

For those interested, here is the actual schematic. 110v is shown in dotted lines.
No issues with factory switches, remember to change the fuse value and use the correct type of fuse!