My OR120 MV Is squealing like mad.

[Gladmarr]

If he'll switch the wire to the correct connection for free, take him up on it. It might be worth questioning if you actually needed the output transformer replaced though. If he can't troubleshoot this problem, who's to say if he troubleshooted (troubleshot?) the last one correctly? You might want to get a second opinion.

...and people wonder why I have no respect for amp techs.....

[OrangePaul]

Some Marshall amps tap off the 8 ohm connection for negative feedback so that's probably why he made the mistake..

[Frank_Jeeves]

Gladmarr. The Ot did need to be replaced. before he did that he replaced the tubes and that didn't work. At the time the amp literally lost it's volume and was weak and over driven in sound. after he did the OT the amp never made that noise again. He tested it for awhile before making sure it wasn't the OT. So yes he fixed the OLD OLD problem but a new one developed after the old one. With the new one I can play it but it seems more sensitive then before the ot needed to be fixed.

[Frank_Jeeves]

I did the mod on the ohm selector and it seemed to clear up the problem. Now the amp is giving me more manageable feedback. thanks guys. A customer of mine is asking if the new transformer could lead to reliability problems down the line?

[jontheid]

Glad it is working well now. Can't really comment on reliability, as A. Hun states in the other thread, it is probably best to contact Orange regarding this.

My amp tech said it would only change the presence if I switch the wire

I wouldn't use this tech again, ever.