Miller Thunderbolt 225 won't weld in high range, please help

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Hi Folks,I've had this little AC welder since the 80's. Some years back I noticed when I plug the lead into the high range side (40-225) It acts like it's only putting out 40-50 amps. Even if I crank it up to 200 amps and try to weld with an 1/8" 6011 the rod just sticks, even when it doesn't stick there's not enough juice there to start a puddle. But when I plug the lead into the low side (max 160) it welds fine. No sticking, plenty of juice. This hasn't really been a problem because most of my welding so far hasn't needed that high range.Something to note, I usually run this machine from a home made "extension cord". This is really some large gage wire with male and female 220 plug/receptacle on the ends. My dad was an electrician and seemed to think with the amperage the welder needed the size and length of the "cord" would be fine. Can you guys please help. I really need to get that high range working really soon.thanks in advance for any helpMikeLast edited by Mike W.; 10-29-2015 at 09:32 AM.
Reply:Can your dad (the electrician) have a look at it to see if its something obvious?
Reply:Probably a bad connection inside the machine where the lead plugs in.
Reply:he's not available but I've dinked around enough I can see obvious stuff and didn't really see anything that stood out like burned windings. thanks for the reply
Reply:Originally Posted by M J DProbably a bad connection inside the machine where the lead plugs in.
Reply:Can you beg borrow or steal a digital clamp-on amp meter?   Home Depot sells them for about $60.00.   That will give you an idea maybe of how many amps are pushed out when welding.  Is the inside of the welder clean, or full of dirt, mouse nests and corrosion?http://www.homedepot.com/p/Klein-Too...L200/202521277A Liberal is someone who lives in a gated community with private security,  but says that a boarder fence won't work and people don't need guns for self protection.
Reply:that's a pretty simple machine. I had the AC/DC version for a few years. About the only things it could be is a broken conductor from the transformer, a bad transformer winding or corrosion on the connector. I mean the schematic on one of these is as about as simple as it gets. Miller Multimatic 255
Reply:Note that the "HIGH" range is actually lower open-circuit voltage than the "LOW" range. (See the schematic in Louie's post above) 7018s and 6011s do not run well in the HIGH range, but it is OK for 6013 and 7014 electrodes. The LOW range has plenty of current for 1/8"7018 or 5/32" 6011.JohnA few weldersA lot of hammersA whole lot of C-clamps
Reply:Originally Posted by Silicon-basedNote that the "HIGH" range is actually lower open-circuit voltage than the "LOW" range. (See the schematic in Louie's post above) 7018s and 6011s do not run well in the HIGH range, but it is OK for 6013 and 7014 electrodes. The LOW range has plenty of current for 1/8"7018 or 5/32" 6011.John
Reply:This issue is resolved guys. I think it was a combination of corrosion and the 7018 not like that higher amperage. Actually traded it to a guy who wanted a stick welder instead of his mig. I been wanting a mig for a while so we're both happy!thanks again for all the responses!