blowing a fuse...

[superechotwin]

got a fender 75 for free (because it doesn't work) but the fuse keeps blowing as soon as i plug it in (power on the amp is off)...i am using the correct fuse (2.5 slo-blow)

[deeval]

sounds like a power trans problem,rectifier tube if it uses one,if no tube then check your rectifer diodes.

[slider313]

Check for a short/burnt or frayed wire on your power cord.Open up the amp and be sure they're making a connection.

[superechotwin]

no rectifier tube... hoping it is something simple like the power chord. One of the transformers does have some writing on it like it was worked on or replaced...thanks

[Blue Strat]

Try pulling the 6L6GCs and try again. It could be a shorted 6L6.

[frankencat]

Check the power cord for damage. If the cord is not damaged then follow it up the line. Could be the power trans or whatever is between the plug and trans. That's where I would be looking anyway. Also could maybe be a bad switch??

[jay42]

There isn't a lot happening between the AC cord and the power switch. There could be a short at the courtesy plug (arc'd over) or hot to chassis from a loose wire or via the Ground switch/death cap mess. You want to get rid of the Ground switch/death cap anyway. If you can't see a burn spot , then you need to undo the hot (black) and neutral (white) wires and verify every piece, including the fuse holder.

If you don't do electronics/soldering, find someone who does. That amp could have 500V sitting on it's power caps...not likely, but possible.

[slider313]

Try pulling the 6L6GCs and try again. It could be a shorted 6L6.

Mike I believe he said the fuse blows as soon as he plugs it in;without the power switch on.That would rule out the power or rectifier tubes.

[frankencat]

Yes PLEASE, this all assumes you know what you are doing. If you don't know how to be safe around the insides of a guitar amp then please take it to a tech.

[superechotwin]

i did take out the power tubes to try them in my regal one at a time... both worked fine. and yes, the power switch on the amp is off.

[Blue Strat]

Mike I believe he said the fuse blows as soon as he plugs it in;without the power switch on.That would rule out the power or rectifier tubes.

Oops! He does say "power on the amp is off". Not sure what that means.

[superechotwin]

thanks for the help/ideas... i'll look into these issues as soon as i can (i still hope it's the power chord - oh well, it was free)

[RussB]

Power Chords are what Pete Townsend played...

An AC power cord is what may be at fault :)

Do you have a DMM, and know how to use it?

[superechotwin]

the power switch or the wires connecting to it showed a short - would this cause the fuse to blow (again, the switch is in off position when fuse blows)
ALSO:
does anybody know who Fender was buying tubes from in the early eighties? they match the writing on ge/rca but without the logo (made in u.s.a.)

[jay42]

the power switch or the wires connecting to it showed a short - would this cause the fuse to blow (again, the switch is in off position when fuse blows)
ALSO:
does anybody know who Fender was buying tubes from in the early eighties? they match the writing on ge/rca but without the logo (made in u.s.a.)It sounds like you've opened it? Since the fuse blows, the problem is after the fuse holder. The On/Off switch should not show as a short, however, you have to disconnect one side to test it, since the problem could be elsewhere. If you have a bad switch, there could be more problems downstream, like a shorted diode in the bridge...no schematic, but i bet it's a bridge. The switch could be shorted to itself, which means the amp is always on, when plugged in. Alternatively, it could be shorted to the chassis, which should be a rare failure, but would explain everything.

In the early 80's, Fender used Sylvania STRs, but they may have been changed out.