Help needed, amp dead

  • Thread starter Thread starter guitarmike
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guitarmike

guitarmike

Well-known member
I was using one of my Friedman modded Marshalls last night, worked great. today, it will not turn on. Turned out to be fuse. The amp has blown fuses 2 times when shutting it off one day and turning it on the next. The tubes are new, tested. Could I be losing a power transformer. Once i replace the fuse I am good for 1-2 months.

Any ideas for troubleshooting?

Mike
 
guitarmike":1qfw1e7y said:
I was using one of my Friedman modded Marshalls last night, worked great. today, it will not turn on. Turned out to be fuse. The amp has blown fuses 2 times when shutting it off one day and turning it on the next. The tubes are new, tested. Could I be losing a power transformer. Once i replace the fuse I am good for 1-2 months.

Any ideas for troubleshooting?

Mike
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What model amp & how long since you had it modded?

This wouldn't be the amp that was modded by FJA is it?
 
Just to be clear, the amp works fine, I turn it off and sometime between turning it off and turning it back on the mains fuse blows. This has happened 2 times in the last 1-2 months. The tubes are new and I tested them, they seem fine. Could the power transformer be going? The amp is a 1975, original iron.

Mike
 
while you're waiting for an answer you might want to try the "tube amp debugging page" and follow the "order of suspicion" for the symptom you're experiencing.
 
Its tube related. 99% of the time its that. Or the surge is taking out the fuse. Are you using slo blow fusses? and the right value?
 
Thanks Dave, I'll double check when I get home but I think I am using 2 amp slo blo.
 
Is it a 50 watt? also if you take the tubes out and put a new fuse in and then turn the amp on [without tubes]. If its a problem with the amp it will still blow. If not tubes are it.
 
I simply changed the fuse and it worked. The last time this happened it worked for 4-5 weeks, then shutdown one day and it will not power up the next. the amp is 100 watts.
 
the 2 amp main fuse. it did not blow with the tubes out. It is just weird because it doesn't pop all the time.
 
guitarmike":12ht9714 said:
the 2 amp main fuse. it did not blow with the tubes out. It is just weird because it doesn't pop all the time.
Click to expand...
Sounds like a tube Mike. I'd swap them out.
 
Well if the amp is in the U.S. and its a 100 watt. The mains fuse should be a 4 amp slo blow. THe HT fuse should be a 1 amp slo blow. If you have a 2 amp in the mains its to small.
 
Dave,

Thank you for helping, after installing the 4amp fuse I have not had any issues since. I think what happened is one of the tubes blew taking out the main fuse. I replaced it with a 2 amp since that is what Marshall has it marked as. The 2 amp fuses blew every so often making me think something was messed up.

thanks again Dave!

Mike
 
actually i've seen this before,..the amp is probably marked 2amps@220/240 and 4amps@120 but the first one on top shows the 2 so it looks like its a 2,...but its a four but if you look and it doesnt say that or it shows a definite 2amp@120 you might to re-think putting a 4 amp in there
 
How did that happen? If you plug a amp in with out a load the fuse won't blow unless a tube arcs or something.
 
Dave,

The fuse either blew when I turned it off or back on. The last time the 2 amp fuse blew, I played the amp at low volume for 1-2hrs at night, turned it off and went to bed. The next day i took it to church and it wouldn't turn on until I changed the fuse. As soon as i put the 4amp fuse in as you suggested, the problem went away. I have played at church 3-4 times with it and played 4 gigs. I have an old Heathkit tube tester and the tubes tested good. Is there anything else i need to be concerned with?

Mike
 
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