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This is an ultra simple mod. Printed Circuit Board (PCB) stays in the chassis !
Properly discharge power supply caps**. Remove Chassis from amp. Locate R12, near V6. Tubes number consecutively V1, V2, etc... from the right side of the amp to left when looking from the back. Gently lift (pry) the lead on the side of R12 that's *away* from V6 up a millimeter or so from PCB to make room to solder. Do not disconnect.
With a low watt pencil, solder 24 ga wire at that point. Do not overheat, lest you release the resistor from the PCB! Now clip the side of R12 closest to V6, if you want the option of putting things back. Or, remove R12 altogether with another snip, leaving your new connection, of course!
Find R25, physically near to V3 (it actually connects to V4B). Lift (pry up, as before) the R25 resistor lead up from the PCB on the side *closest* to V3. Solder your wire to that point.
For dress, plan your wire length so it can come up toward top of amp for the run, to avoid oscillation from stray PCB signals. You are done! Install chassis.
This mod gives the reverb and vibrato to both channels. The normal channel now sounds very much like the vibrato channel with the bright cap clipped. They are now in phase, have similar gain, and may be bootstrapped (jumpered) together with a patch cord, which now works fine at any volume and gives a satisfying OD tone and some more volume.
Pic located here - http://www.fenderforum.com/userphotos/index.html?recid=64923
[YMMV and Fritz_D_Cat or any of his likenesses is not responsible for any damage or injury because you messed with a perfectly good amp]
** DISCHARGING THE CAPS
Since you're going to have your solder iron out, why not make a discharging tool? Buy an alligator clip lead and resistor at Radio Shack. Snip the alligator off one end. Solder the resistor, any value from 1k to 10K to the snipped end of the lead. Good idea to insulate with electrical tape or shrink sleeve from the body of the resistor to the wire insulation.
Unplug amp from wall. Remove tubes. Label them so you get them back in the right places.
Clip alligator to chassis. Turn standby switch to "on". Touch resistor lead to each pin slot of the second tube socket from the left, looking from the back, for 30 seconds, being careful NOT to be touching anything conductive.
Use one hand only, for best safety. Be sure the resistor lead you are using as a probe is making contact with the metal of the pin slot in each case. A flashlight in the other hand is useful.
If you know which socket pin to touch, great. If not, just do them all.