Fender fiber eyelet boards

[BluegrassDan]

I frequently have to address vintage Fender amp fiber eyelet boards that become hygroscopic and conductive. The PSU filter boards and bias boards are easy enough to disassemble, remove the dirt and wax, use a heat press on them, and reassemble. The internal boards usually involve a heat gun and alcohol.

Has anyone developed a method for sealing and/or treating these fiberboards to eliminate the possibility of them becoming conductive again? I have some ideas of what to try, but I thought I’d ask around first.

 

[CJ]

If they are wax dipped like pre CBS stuff then it is a pain,

Post CBS I use clearcoat, not very fun to solder on after you spray the board ,

You can also mount the 220k grid resistors to a a solder lug terminal thingy off the board, as the junction of these resistors and the HV phase inverter resistors are only about a 1/4" apart, I leave the cap side eyelets alone and flip the resistors backwards toward the tone pot area. Runaway bias on the pwr tubes is the biggest problem with a conductive board. Microphonics can be a problem too, I remove the center screw on the board and this helps a bit. I solder the solder lug thingy to the chassis so the customer does not complain about a hole drilled in their 65 Deluxe Reverb.

Buying a new board set from Mojo is a labor intensive job on the big amps, but it is a good time to clean the gunk off under the brass ground plane,

I have all the colors and wire lengths for the ab763 written down along with the locations which can save a little time,

Strangely enough the best sounding Fenders I have worked on had warped and conductive boards, that's why I leave then alone and flip the grid resistors.