Fender Twin 65' reissue - keeps blowing fuses/no output

[Libertycynic]

Hey guys, first post here. Hope you can help.

I've got a Fender Twin 65' reissue (blackface with a circuit board instead of hand wiring). It draws power and the tubes warm up on standby, but as soon as i hit the power switch, the fuse blows. At first I thought the output transformer was the problem, but ive replaced it and im having the exact same problem still. No burns or loose wires in the guts and all the tubes are good.

Any ideas?

[Justin Thomas]

Geofex.com

Look in the top left corner, the tab for "Tube Amp Debug Page." It could be any number of things - rectifiers, bad filter caps, obviously there's a short somewhere. If nothing else has been done to the amp lately and it worked up to this point, it's likely something that has failed... But don't just throw parts at it on a hunch or because someone else had the same problem and "this or that" fixed it. Troubleshoot the amp. Does it blow fuses with the power tubes removed? Also, google "light bulb limiter" and build one; it will save you needlessly blowing fuses.

Also, for future reference, it's more likely to be ANYthing else before a transformer...

Justin

[52 Bill]

Hey guys, first post here. Hope you can help.

I've got a Fender Twin 65' reissue (blackface with a circuit board instead of hand wiring). It draws power and the tubes warm up on standby, but as soon as i hit the power switch, the fuse blows. At first I thought the output transformer was the problem, but ive replaced it and im having the exact same problem still. No burns or loose wires in the guts and all the tubes are good.

Any ideas?

Welcome to the place.

I assume that you mean the standby switch, as the filaments would not heat up unless the power switch was turned on. The first problem is normally power tubes. Remove the 4 6L6 tubes and turn on the amp and then hit the standby switch. Does the fuse still blow?

[mtlbasslad]

Have to agree with Justin, build a light bulb limiter right away, saves trips to the store for fuses...
For those who are worried about where to get incandescent bulbs - they still make them, but now they're called 'specialty' bulbs. Just got some at Home Hardware - 'rough service bulbs' 50 & 100 watt.

[Libertycynic]

Took the tubes out and switched it on and the fuse didnt blow. Does that mean it needs new tubes?

Thank you guys for even replying to this. Im sure ive gotta look like a doofus, but ive gotta start somewhere.

[Axtman]

Took the tubes out and switched it on and the fuse didnt blow. Does that mean it needs new tubes?

Yes that probably means one or more of your output 6L6 tubes has a short. Do you have access to someone with a tube tester?

[glebert]

Took the tubes out and switched it on and the fuse didnt blow. Does that mean it needs new tubes?

Thank you guys for even replying to this. Im sure ive gotta look like a doofus, but ive gotta start somewhere.

Probably also want to measure your voltages at the tube sockets to make sure that a bad tube didn't take out a resistor.

I've looked like a doofus here more times that I would like to admit and people are still helpful. It's a pretty cool place.

[nevetslab]

And, take a look at the four 470 ohm screen resistors. Fender solders them between Pins 4 & 6 on each poer tube socket. They often blow when a tube blows. Also, while you have the tubes removed, measure what the bias voltage is at R44/R45 (pair of 220k resistors) that feed the grids of the power tubes. It should be in the range of -52VDC. If instead it's a vary low neg voltage or 0V, that would be turning on the power tubes hard and draws loads of current.