Rectifier for lincoln tombstone

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I got these old lincoln ideal arc 250 ac/dc stick welders from a school.The tombstone kind with the round top .Was told they run but only on AC  because of kids screwing around and switching the polarity  under load the rectifiers were shot.. Was wondering how much a new rectifier would cost for one of these things.. Just hoping its not something llike 500$ which is what I was told,( but Im unsure of that)Last edited by ak4130; 11-14-2011 at 03:51 PM.
Reply:If we went with caining in this country, those kids wouldn't be beating up a defenseless awesome welder.I don't know about the rectifier, but I picked up an AC/DC Idealarc 250 for $104.50. That was the lowest I've seen. The high being around $500.00. Keep a search going for one smashed up or so. What a shame, I hope you find one."Where's Stick man????????" - 7A749"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding"Stick-man"
Reply:Originally Posted by ak4130I got these old lincoln ideal arc 250 ac/dc stick welders from a school.The tombstone kind with the round top .Was told they run but only on AC  because of kids screwing around and switching the polarity  under load the rectifiers were shot.. Was wondering how much a new rectifier would cost for one of these things.. Just hoping its not something llike 500$ which is what I was told,( but Im unsure of that)
Reply:http://www.ebay.com/itm/NEW-BRIDGE-D...#ht_1908wt_907this ebay seller seems to have 3 phase rectifier modules listed all the time.  Or, you could get individual diodes and use them.   $65 seems like a good price for a 300 amp bridge. He has a 500 amp unit, and a differnet one with a build in heat sink for a bit more.miller syncrowave 250hobart handler 140home made 400 amp engine driven in progress...
Reply:If it doesn't weld on DC because the polarity was switched under load, it may be the switch, not the rectifier that died. If I were you, I'd check the polarity switch contacts before I replaced diodes.JohnA few weldersA lot of hammersA whole lot of C-clamps
Reply:Get an ohm meter and test the diodes, looking for shorts. If they have been welding in AC with out problems and no conductors have been disconnected, Then the diodes are most likely OK and the polarity switch is shot. Replaced only a few diodes, but have replaced and lot of line and polarity switches.The diodes are in circuit all the time, only the output terminals are switched from the DC to AC circuits,
Reply:Appreciate the replies.. Took it into work,hooked it up  struck some arcs on ac, but it was kind of a weak arc..BUT The thing is though the big knob on front is super sticky, not sure if its even working , the little pointer doesnt work either so what amps it was set on is a ? Also struck an arc on DC and it arcs, but there was a louder than average buzzing coming from the machine,so didnt mess with that.. Will check diodes with an ohmmeter tommorow.Going to clean the big knob up good too... Also code is 7925-c and the serial # is AL 407465 thanks