Tube bass amps- Leading causes of fuse blowing

[pbman1953]

I know someone that has a Fender Super Bassman that is blowing fuses. He's at the point of dumping it for sale, so he doesn't have to fix it.


He said that the main amp fuse is blowing so I'm asking for the leading causes  to know if it's worth putting money into it.
 
The amp has 6-6550's and each pair has a protection fuse.


Off the top of your head, what stands out, and on those thoughts, what would you estimate for a cost if it was a hardware part, ex: tubes, OT or PT


Thanks

[Platefire]

Hello, first you need to provide some up front information before anybody can provide good information back to you likewhat model # amp, a schematic, which fuse is blowing. Cost??? it could be just a simple cheap solution all the way up to a power transformer---$200, depending what the problem is. The replacement of 6 of those power tubes would be pretty expensive, if it neededthat. Are you going to be troubleshooting this amp??? Platefire

It sounds like the Bassman 300 with six 6550's linked below?
https://medias.audiofanzine.com/files/bassman-300-pro-fba-schematic-rev-d-474680.pdf
 

[pbman1953]

It's the Fender Super Bassman-


https://www.fmicassets.com/Damroot/Original/10001/2249000_bamp_manual_all.pdf


I mentioned that main amp fuse was blowing.


Me trouble shotting possibly or I may take it to a tech

[AlNewman]

The manual you linked doesn't show a schematic, but it could be a tube thing.

Pull all the tubes, and see if the fuse still blows, (a light bulb limiter is a valuable tool).

If the fuse blows with the tubes out, take it to a tech.

[pbman1953]

The manual you linked doesn't show a schematic, but it could be a tube thing.

Pull all the tubes, and see if the fuse still blows, (a light bulb limiter is a valuable tool).

If the fuse blows with the tubes out, take it to a tech.

All tubes or only the power tubes?


Thanks!

[pbman1953]

Also, finding the schematic was not possible online

[Platefire]

This amp is somewhat more complex than the classic amps I'm use to working on which simply means there are a lot more things to go wrong to cause problems.On the classic amps in a case like this blowing main fuses, we remove all the power tubes to take the main load off power supply. Usually leave the pre-amp tubes in place.If the amp still blows a main fuse with the main load removed it most likely was a bad rectifier or a bad power transformer or bad power tube. If the fuse doesn't blow with the main load removed, it's a good chance it's just a bad power tube that could further point to in-correct bias. As already mentioned a light bulb limiter is a valuable tool in trouble shooting to help prevent doing more damage when powering the amp up. So firing it up with the power tubes out on a LB Limiter would be the first step in determining where the problem is at

[tubeswell]

Same main causes as most other tube guitar amps

[pbman1953]

This amp is somewhat more complex than the classic amps I'm use to working on which simply means there are a lot more things to go wrong to cause problems.On the classic amps in a case like this blowing main fuses, we remove all the power tubes to take the main load off power supply. Usually leave the pre-amp tubes in place.If the amp still blows a main fuse with the main load removed it most likely was a bad rectifier or a bad power transformer or bad power tube. If the fuse doesn't blow with the main load removed, it's a good chance it's just a bad power tube that could further point to in-correct bias. As already mentioned a light bulb limiter is a valuable tool in trouble shooting to help prevent doing more damage when powering the amp up. So firing it up with the power tubes out on a LB Limiter would be the first step in determining where the problem is at

Thanks, I'll pass this on