bscenefilms
Active Member
I have a Marshall JCM900 SL-X 5881 that has Raytheon NOS tubes in it - They have about 40 hours of play time on them. Last jam I had, the amp got lower and lower in volume until it finally made some horrible noise and died. Power light still on - but whisper quiet output...
Now, the amp had died on me about a year ago after it overheated when a band mate covered the vent on the top - I took it into a shop to get it repaired and they repaired the bias circuit and replaced the stock tubes with what I described above.
So about $400 later and I had the amp back. About 10 hours of play time and it blew the main power fuse. It was a 5A slo-blo and I replaced it with a 4A slo just to be safe - That one blew after about 4 more hours. This last time I replaced it with the stock 5A slo and that is when the amp exhibited it's current symptoms...
Now I can take the thing in and blow another $400 or whatever and have no guarantee that I will have my amp back in a reliable form...
On another forum it has been suggested that the power transformer is damaged and needs replacement. I have a decent multi-meter and an oscilloscope that I use for digital circuit testing / development.
I understand power supplies in general but it's not my forte`. How can I test the power transformer to determine if it is indeed the issue? I see where I can get a replacement one for about $120 online and I am happy to do the repair myself if this will indeed fix the issue.
Thanks all!
Mike
Now, the amp had died on me about a year ago after it overheated when a band mate covered the vent on the top - I took it into a shop to get it repaired and they repaired the bias circuit and replaced the stock tubes with what I described above.
So about $400 later and I had the amp back. About 10 hours of play time and it blew the main power fuse. It was a 5A slo-blo and I replaced it with a 4A slo just to be safe - That one blew after about 4 more hours. This last time I replaced it with the stock 5A slo and that is when the amp exhibited it's current symptoms...
Now I can take the thing in and blow another $400 or whatever and have no guarantee that I will have my amp back in a reliable form...
On another forum it has been suggested that the power transformer is damaged and needs replacement. I have a decent multi-meter and an oscilloscope that I use for digital circuit testing / development.
I understand power supplies in general but it's not my forte`. How can I test the power transformer to determine if it is indeed the issue? I see where I can get a replacement one for about $120 online and I am happy to do the repair myself if this will indeed fix the issue.
Thanks all!
Mike
