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Hello All! New to the forum...I have a Sunn 300t amp that I need a bit of help with.
A bit of background - this amp was given to me by the music store i frequented in high school (it was a small town, and i was a great customer). The owner gave it to me, it was brand new but not working and he couldn't figure it out. The amp kept blowing the main fuse and he assumed it was either the transformer or the tubes. Either way at the time he'd already lost the bill of sale, Sunn had been purchased by Fender and the cost of repair outside of a warranty versus what he'd actually paid for the thing would have been a loss so it was my lucky day!
Knowing nothing about amps (just that this appeared to be a much larger version of my silverface bassman) the beautiful monster just sat there as a paper weight for about 10 years.
Now I know a little bit more so i've decided to repair it. I replaced the main fuse and bought some extras to give me a few chances. To my surprise the unit worked instantly. I plugged up a bass and I was good to go, or so i thought.
I used it for about 8 practices without issue, then one day I tried to use the line out and there was nothing. I gave up on the DI out and decided to mic it. Once I unplugged the DI out the amp played fine but then after about 30 minutes my tubes started glowing red, we smelled smoke so i turned it off and unplugged the amp from the wall.
I'd already ordered a matched sextet of 6550's (the Fender Red's, just like stock) because they're getting a little harder to find. Supposedly there is no need to bias these as they're color coded; per fender. I decided to replace all and bias anyway just to be safe, after all my tubes were just glowing red and smoking. The manual suggests 100 mVDC so I turned it till it hit fine, then as instructed I moved the multimeter to the balance points and set it as 0 VDC...now as I was moving it I noticed it stays at 0, no matter what I do- all the way to the left all the way to the right still 0.
I started playing bass and within about 10 minutes I smelled smoke, I ran to the back and noted that now 3 of the power tubes(the one's on the right side of each grouping as you face the back) are glowing hot red! The tube indicator lights are still green but of course I threw it into standby and powered off.
At this point I'm about to give up but I found this board and saw a lot of really informative, helpful posts so I'm hoping someone out there has an idea for me - anything would be appreciated, thanks for reading the novel.
Cheers!
-Van
A bit of background - this amp was given to me by the music store i frequented in high school (it was a small town, and i was a great customer). The owner gave it to me, it was brand new but not working and he couldn't figure it out. The amp kept blowing the main fuse and he assumed it was either the transformer or the tubes. Either way at the time he'd already lost the bill of sale, Sunn had been purchased by Fender and the cost of repair outside of a warranty versus what he'd actually paid for the thing would have been a loss so it was my lucky day!
Knowing nothing about amps (just that this appeared to be a much larger version of my silverface bassman) the beautiful monster just sat there as a paper weight for about 10 years.
Now I know a little bit more so i've decided to repair it. I replaced the main fuse and bought some extras to give me a few chances. To my surprise the unit worked instantly. I plugged up a bass and I was good to go, or so i thought.
I used it for about 8 practices without issue, then one day I tried to use the line out and there was nothing. I gave up on the DI out and decided to mic it. Once I unplugged the DI out the amp played fine but then after about 30 minutes my tubes started glowing red, we smelled smoke so i turned it off and unplugged the amp from the wall.
I'd already ordered a matched sextet of 6550's (the Fender Red's, just like stock) because they're getting a little harder to find. Supposedly there is no need to bias these as they're color coded; per fender. I decided to replace all and bias anyway just to be safe, after all my tubes were just glowing red and smoking. The manual suggests 100 mVDC so I turned it till it hit fine, then as instructed I moved the multimeter to the balance points and set it as 0 VDC...now as I was moving it I noticed it stays at 0, no matter what I do- all the way to the left all the way to the right still 0.
I started playing bass and within about 10 minutes I smelled smoke, I ran to the back and noted that now 3 of the power tubes(the one's on the right side of each grouping as you face the back) are glowing hot red! The tube indicator lights are still green but of course I threw it into standby and powered off.
At this point I'm about to give up but I found this board and saw a lot of really informative, helpful posts so I'm hoping someone out there has an idea for me - anything would be appreciated, thanks for reading the novel.
Cheers!
-Van
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