Replacement Gallien Krueger transformer (240v to replace 110v)

[dangerboy]

I have an old Gallien Krueger 250ML (guitar combo) but it's annoyingly 110V so it needs a big transformer to plug into in the UK. 

So I thought, why not have a look inside and see what I can do? I don't really care about it but fixing it seems fun.

 

It has a big chassis transformer mounted inside. This is labelled "00617 MAGCOMP MC-1724 8811". It has five leads coming off it labelled 1,2,3,4,5

Here is the schematichttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/%23pro_audio/Gallien-krueger/Gallien-krueger_250ML,_250RL,_212SCL_Service_Manual.pdf

 

Are any of you wise in these things and can point me at an equivalent designed for 240V mains?  

 

I took it to an amp tech but he kept it for a month then gave it back to me, saying the change was "uneconomic". But it seems like a fun project. 

[ClusterOne]

Hi,

 

Not going to be of much help but i can see the output from rectifier is +45V and -45V so perhaps secondary winding output of transformer has to be in such region. As that is what feeds rectifier.

 

I don’t remember much from college (studied electronics extensively) but i can imagine two wires on input (240V) so them three should be related to output..

See diyaudio website, people there design their own amps and perhaps someone there could help on how to go about sourcing appropriate transformer for your amp.

Edited 3 hours ago by ClusterOne
..220V to 240V to avoid confusion :)

[DGBass]

Something like this if you can find one would probably be usuable. This one has a 230V ac primary, and a 32.5Vac - 0v - 32.5Vac secondary. It was salvaged from an early 80s Carlsboro 100 watt pa amp and is likely rated around 100 - 120VA. The 250 ML is a 50 watt per channel unit so you will likely need a transformer rated around 100 - 120VA. The GK diagram also notes the mains fuse should be T 1 Amp for UK operation so you would need to change that from the current 3 Amp fuse for 110-120v working. The fuses for the transformer rails ( the 32-0-32 outputs) remain the same. You could also go all fancy and fit a modern toroidal transformer. Ideally one with a 240V primary, and around 30-33v ac dual secondary. That should give you around the 45-0-45v rectified supply you need to power the amp. It's not rocket science, but it is messing with mains voltage so a great deal of care is needed to avoid any unpleasant outcomes. Just saying. Maybe a different tech might help you out and it may even be worth emailing Gallien Krueger to see if they can suggest a modern part to replace the 110V-120V transformer. They may also be able to offer any insight into anything else you might need to factor in to a voltage conversion.  

 

 

[ClusterOne]

..Dumb me.. The third wire would be a common ground/0V..

 

As what @DGBass says about voltages seems to be correct according to the online converter.The only thing left to figure out is how many Amperes the transformer has to be able to supply safely.

Which should not be that hard to figure out as long as you know the wattage of the amp.

But again, I don’t remember much of the stuff as it has been decades since college but briefly P= U*I 

where P is the power in Watts, U is for voltage & I for current (amperes).

(Hope i am not terribly wrong here as unsure how exactly this applies to amplifiers but dumb light bulb wattage can be worked out like that I think..)

Hope someone can shed some light on..

Edited 3 hours ago by ClusterOne