The notorious problem with band/stage amps, the guitar/mike leads making
poor contact inside the sockets.
For anyone saying replace, move to another thread.
I don't see the point in replacing with much the same, that will also weaken
at the bend, over a few years of use.
The tip contact has to repeatedly lift over the tip and then drop down into
the groove. The ring contact/s don't have to do this so rarely a problem
there. Coupled with more "leveraged" movement at the tip with lead tugging.
Requirements some 2mm silicone rubber cord from a fishing/angling supply
shop
Hama/Perler/Pearler beads about 2.5mm internal bore, (small coloured plastic
rings) for making "mosaics" on a sort of pegboard from kids/craft shops
Bit of looped copper wire as a "needle threader"
Artery forceps, again from an angling shop, or similar tool.
Thin nose pliers
Assuming chassis mounted , then cut a piece of cord 100mm long.
For pcb mounted ones then about 120mm and suitable 4x 2.5mm holes drilled
through the board. Being rubber you can safely deill through a track or two
if constricted space (caution if for speaker sockets).
No need to desolder any wires.
Pics below are against 1mm square graph paper.
http://home.graffiti.net/diverse:graffiti.net/jsb.jpg
First one takes about 10 minutes to complete and about 5 minutes each, when
familiar, for the chassis mount socket type.
First shows the "needle threading" action.
Second is the main assembly, thread 2 beads onto the doubled-up cord leaving
a loop.
Place a third bead in this loop and pull the tails to tighten in place.
Place in orientation over the contact as in the pic.
Take one tail around the pin edge furthest from the mounting panel, under
the socket and back up the other side of the other pin.
Grab this tail with pliers, 10mm back from the free end, and slide through
the bead in the loop, the cord will be under a bit of tension.
Anchor the free end with forceps.
Lace the other tail to form a cross under the socket
Reuse the threader , pushed through the bead in the loop.
Trap the free end of the second tail in the threader, a few mm back, and
pull back through the bead.
2 such pieces of cord will anchor themselves quite well in a bead but to be
sure, balance up the 2 free tail ends and anchor both together with the
forceps, while finishing off.
You can then pull the bead through the loop to its final locked in position.
Position all the sections of cord and top beads so near enough equal tension
throughout.
Remove the forceps and melt a spot of hot melt glue between the 2 tail ends
The insertion and pulling-out force for any 1/4 inch plugs is then noticably
greater and much more reliable contact in use.
Makesure the hot-melt or beads are not near any hot components when
reassembled.
And guitarists can throw away those cans of contact spray

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/