Mesa Boogie Mark 3 Gain Loss

[sixstring63]

2.5 amp 250v slow blo fuse is what was in it .

[sixstring63]

It's Up and Running

I have got the Boogie up and running and sounding good.The problem was what I had in the back of my mind for the past week,it was the 3 30uf 500v caps in the power supply I replaced , for some reason rather they are bad or what I don't know but I put the old caps back in a Bingo ! fired right up and works fine and the voltages are just about up to spec within 7-8 volts. I put in F+T brand caps, should have went with Sprague (live and learn).Thought I was doing right replacing caps on a 25 year old amp but ended up being a major headache.Replaced bad 3300uf cap in heater rectifier which was bad and replaced the bias caps (Sprague) thank God ,now that the heater voltage is good it sounds almost as good as new. It has been a great learning experience and a little frustrating at times because I was careful and sure I put everything in and back together right. Thanks for all the good advice and help guys.

Mike

[pdf64]

Well done - you've been extremely unlucky to get a bad F&T cap, they have a great rep, better than Sprague, I think many top end manufacturers use them now. Only 1 of them will be bad, most likely the one downstream of the 5k6 dropper. Your Sprague caps haven't got any better and will need replacing sometime. Maybe best to do it while the procedure is fresh in your mind. At least assess their performance by measuring / recording the ac ripple voltage, check there aren't any bulges / leaks in the casing and end seal. Peter.

[sixstring63]

Old Caps

The old caps looked physically o.k. with no bulges or leakage. I put the scope on the circuit after I installed them and the signal was as flat as a pancake ! so I think we are good to go for now. Voltages are just about perfect. I think I'm going to start an tube amp kit next , this fix has given me confidence to move on to a bigger challenge. I have learned a lot from all you guys and from a book from Dan Torres that was really helpful. Just did some stomp box mods and sold a few of them today. This guitar tone thing is as fun on the tech end as the playing end that I've done for 30+ years.

MIke

[sixstring63]

Mesa gone bad again

Hey Guys , Thought I had this Mark 3 thing all worked out but I guess I was mistaken. Recently I was playing and had a chance to crank it up good for the first time since doing the other repairs and it sounds good up till about 1.5 to 2 on the master and after that it gets bassy , flubby and mushy and the top end seems to roll off with no definition or tone that you can even work with, plus the volume does not really go up but just gets more muddy.I changed all the tubes but no go. I was using the amp at a lower volume for a few months and seemed to sound pretty good but sounds bad above 1.5 now. Any ideas ?

Thanks Mike