acoustic model 450 blowing fuses

[wardevans]

i have distorted output with nothing plugged in and it keeps blowing fuses. any ideas, output devices???a start would be nice. thanks

[Enzo]

I am not sure how you get distortion with nothing plugged in. DO you mean noise? Distortion requires a signal to distort.

Blows fuses right now every time you turn it on? Or blows them fairly often while otherwise functioning? Does it make a sound as it blows the fuse? A loud sound? If you disconnect the speaker, does it still take out the fuse?

As with any amp that blows fuses, look to power supply and power amp. If the output devices are shorted, go from there. If not, look for shorted rectifiers, filters, or shorts to ground from power rails. The main supply in there is +92v - this is a single sided amp. REmove the wire to the power amp board so the power supply can just sit there. WIll it hold a fuse that way?


If power supply seems OK, check the drivers and predrivers. Is the large output cap shorted? Is the bias string open?

[wardevans]

i picked this amp up a while back and haven't played with it. i don't think it was well when i got it. it makes noise when it is plugged into the cab. yesterday i fired it up and it made a loud buzzing sound with nothing plugged into it and then pop, nothing. so i tried to remove the fuse but had problems with the cap. i removed the fuse holder from the amp and finally got the fuse out to see a shattered fuse inside. i put the holder back in the chassis, resoldered the leads, tried another fuse, plugged the amp in, got an immediate buzz, then nothing. fuse blew. i was thinking the caps need to be replaced in the first place. but i really need a schematic for this thing to track everything down. at any rate, i need a starting point for reference.