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SurfGuitar101 Forums » Gear »

Permalink need help troubleshooting fender excelsior

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Hi everybody, I´m struggling troubleshooting my fender excelsior and need some help.
I bought the amp second hand three years ago, played it only one time a week in the rehearsal room. Except a speaker swap (the classical swap for an eminence legend 1518) and preamp tubes, i kept the amp stock all those time.
Last month, the tremolo stopped working, and two weeks later, one of the power tubes started "flashing" and the internal fuse died.
I replaced the internal fuse, and put some new tad 6v6gt str power tubes. Tremolo was back, but really really weak, almost barely audible.
Yesterday I decided to open the upper chassis (preamp section) to make a visual inspection. Nothing particular to see inside. As the chassis was open, i did a couple of simple popular mods:
replacing the tone switch with a tone knob,
changing r9 and r29 to 10k to increase the tone control range,
changing c2 to 720pF to change the tone contour.
As the tremolo was barely audible, I decided to make the tremolo depth mod as well (soldering a 1Meg pot instead of r15) to see if it could bring back some swampy vibe.
After reassembly, with the depth knob maxed out, the tremolo was back (but still a bit weaker than stock...) The tone mod is working fine. I played two hours, and today... Back to barely audible tremolo Whatever
I decided to make a visual inspection of the lower chassis (power section). It smelled like burned, and the PCB show some sign of "heat coloration" (sorry for my poor English) under the two Sag resistors R22 and R30. I also got the feeling that my power tubes are running really really hot.
Any help would be greatly appreciated. I´m aware of potentially lethal current and know how to discharge capacitors, i´ve got a multimeter, and can solder, i have also done some simple mods following tutorials, successfully build some pedal kits, wiring guitars and so on, but troubleshooting a tube amp on my own is just too much for my skills and lack of theory Confused
here is the amp schematic:
excelsior schematic

Swap out V2 tube first. Check all DC voltages in the trem circuit (lower left hand portion)against what is indicated.

Problem solved! Irf820 mosfet (q1 on the schematics) was shorted and need replacement, but thx ConcreteSurfer for the help.

No worries! Glad you found the issue!

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