Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #88993  by JonnyBoy
 Sat Nov 06, 2010 9:54 pm
I have had the amp (MC50) on my bench for two days and I don't see any shorts, busted caps, anything out of whack. All old caps have been replaced including the cans. Diodes and resistors are all old. It takes a 1.5 amp fuse, moved to a 2 amp fuse and it blows right away too. It has blown fuses in the past here and there, a fresh one did the trick and 6 mos later it would blow, not that big of a deal. but it never has acted like this one after the other within seconds. It did have a slight bang during movement that afternoon b4 gig. This problem started at gig, went through 6 fuses one right after the other, but had a backup amp thank god. Would any of you Amp savvy dudes have any direction for a starving artist that can't afford a personal tech? I have been very sad it is my favorite amp... :cry:

Thank you to all that can help me!
 #89019  by JonnyBoy
 Sun Nov 07, 2010 7:38 pm
bump... Any thoughts or top of the head kind of info would be well accepted. I am hoping it is not the transformer. It obviously has a short somewhere. Hopefully Brad may have a thought on this...... or anyone else that knows even a little something.... Thanks!! :smile:

Can faulty diodes cause shorts since they should travel one direction?
 #89020  by mijknahs
 Sun Nov 07, 2010 9:26 pm
An old Twin I used to own would blow fuses because the filter caps were bad but I have no idea about the problem with your amp. Did you replace the caps in the power supply (the multi-cap "can")?

 #89022  by JonnyBoy
 Sun Nov 07, 2010 9:42 pm
Yes All caps even the cans were replaced. it did take a slight fall during transport, but not a bad one, maybe a half foot off ground, but it is heavy. I ve tested for shorts and current flows through the entire system start to finish. There is one place where current is blocked where the sensor coming off the power supply into the transformer. There is current into and out of the transformer, but I do not know how to test it to see if the transformer has failed or if the power sensor has failed. Does anyone know how to test transformers?

Thanks Jim fore giving it a stab, I will revive this amp even if I have to use another transformer to get it going again. It is almost 40 years old.

****AGAIN DOES ANYONE KNOW HOW TO TEST A TRANSFORMER FOR FAIL?********* Thanks guys this is really a big help, not much on the net about this amp.
 #89031  by JonnyBoy
 Mon Nov 08, 2010 7:14 am
Thanks Jim, I just may do that. I looked on the bay and couldn't find the right one there... Audio classics didn't have one for sale either, but that doesn't mean they don't have one. I got it for such a good deal considering its been reworked and looking shabby, I guess I could put a 100 or so into it, when I have it. Thanks for your help as always, JB.