Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on January 25, 2023, 12:30:26 pm
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I'm have difficulty understanding why the gauge of wire I used to add a presence pot in a PBC Blues Junior had issues. I added a Plexi stye vintage presence, using the gauge of wire in pic below, cloth 22 gauge. Worked fine. I pull the board to do other mods and while I had the bd out again I decided to replace the the 22 gauge wire with shielded wire, two wires and a ground, wrapped in a foil shield, the shield was connected to ground. Assembled the amp, had noise issue and low volume. Tapping the hanging pot, severe noise. I though maybe the shielding was the issue, cut the shield out, still major noise then separated the wiring to presence, still issues. Checked the solder traces on back of bd. continuity on all traces. ??? I knew the wiring was correct, the only change was the gauge of wire I used that had the shield, it was the gauge of wire that's normally used for guitar pickups, like 28, maybe 30. I know there's small voltage on the presence pot but didn't think the small thin wire was causing it. Frustrated, I just rewired the pod back to the cloth 22 gauge like I first had it, bingo noise gone, perfect.Why did the small gauge wire cause an issue..?
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bad mojo BJ.
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All the PI cathode current flows through the 5K presence pot but this is only a few mA. I doubt the gauge of the wire was your culprit.
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All the PI cathode current flows through the 5K presence pot but this is only a few mA. I doubt the gauge of the wire was your culprit.
Same thought's here..?
But, we all know the thin PCB pads are like tinfoil in those BJ boards. Changing the back to the 22 gauge wire, some traces lifted, you can only screw with those pads once. So, I had to fix several traces with small leads, scrap the traces to get a good contact. This time "I coated the repaired traces with clear nail polish", couple of coats. Only thing I can think I can think of is not coating the repairs was causing the problem..? possible..?
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This time "I coated the repaired traces with clear nail polish", couple of coats. Only thing I can think I can think of is not coating the repairs was causing the problem..? possible..?
Probably should have used pink. :l2:
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Probably should have used pink. :l2:
Pink, close enough to the cream board l guess, ha, ha you scalawag. Just kidding :l2:
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... add a presence pot in a PBC Blues Junior ... replace the the 22 gauge wire with shielded wire ... normally used for guitar pickups, like 28, maybe 30. ... Why did the small gauge wire cause an issue..?
With such a small gauge of wire, there's a strong possibility of handling damage & unrecognized breaks. Especially given your description of having the pot dangling.
Separately, shielded wires can have electrostatic noise problems between the shield & the center-conductor, generally related to the insulation around the center conductor. This causes weird static noises when a wire is handled & flexed. This effect lead to some shielded cables having a conductive coating on the outside of the inner insulation, where the shield might move & cause the static noise disturbance.
I'm guessing one of the 2 causes noted above. Either one could be eliminated with a stouter single-conductor wire.
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I'm riding with Reply#1 to the bank :icon_biggrin:
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I'm riding with Reply#1 to the bank :icon_biggrin:
Shooter, come on.. :laugh:
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I'm riding with Reply#1 to the bank :icon_biggrin:
Shooter, come on.. :laugh:
You're probably right, that thin wire being stressed (only connecting by a strain or two most likely) as I worked on the bd, turning over several times to fix traces..? All good now with 22 gauge non-shielded wire. Live and learn, that;s why most of us hate PCB's :icon_biggrin:
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aside fwiw;
after I was out-sourced n down-sized, I hit the road for a couple months, was hitting up music stores for amp-tech work. ran into a nice amp store, they had a good tech, was satisfied, I looked around and NO SS/PCB stuff, so I asked, the guy laughed, said help yourself, "we only take them in trade to get them off the street" He pointed me to the 5 yrd dumpster out back, overflowing with SS/PCB amps.