Airline 2p Loud Hum Troubleshooting

[tako]

Good Evening everyone I am new here and it is nice to communicate with all of you, and I appreciate any and all feedback.

My friend asked me to help him replace the pots,jack, switch, and wires on his Airline 2p. He ordered all the parts: the jack, the 3-way switch, 500k pots, 0.047uf caps, and wire. I noticed that the switch he ordered(crl lever switch with 4 lugs on both sides) is different from the original switch (import style with 8 lugs in one line with two more lugs for ground). I wired everything up exactly how it originally was(except for the different switch, and using all 500k pots this time). The pickups work in all three switch positions, and all of the pots work as well. The only problem is there is a loud hum that only occurs when I turn down any and all volume knobs. The hum is not present when the volume knobs are turned all the way up.

Attachment 1 is the original wiring for the guitar.
Attachment 2 is is how I wired the new crl lever switch.

The original switch had grounds from each volume pot to the ground lug, but the crl lever switch has no lugs for ground. So I placed a ground wire from the neck volume, to the bridge volume, and then to the master volume. So I'm trying to figure out the cause of the loud hum and if I wired the switch wrong. Thanks everybody

[HotBluePlates]

Are each of the pot backs connected to each other, and to a string ground?

[tako]

@HotBluePlates: Thanks for the reply! Yes, I wired each of the 3 volume pots together with the guitar's bridge ground to the back of the master volume pot.

[HotBluePlates]

And both pickups are hum buckers, as pictured? Are the pickup leads just a simple hot & ground, not 4-conductor?

The Neck/Bridge volumes are set up as independent volume controls, with the pickup in on the wiper and out to the selector switch at the ungrounded outer lug. If you have it wired that way, the hum only appears when you turn down from max (introduce some resistance between pickup & selector switch).

Does the hum start right away, or only once you're down to the bottom of the volume knob travel?

[tako]

@HotBluePlates: Again thank you so much for helping me out. Yes both pickups are humbuckers with only a hot and ground each. And if I have the volume turned all the way up, there is no hum. The hum only occurs once I begin to turn the volume down on any of the three pots. As I continue to turn the volume down, the hum gets louder as the volume fades. So once all of the volume pots are at zero, there is only humming.

So you're saying that although all of the volume pots are already grounded, including the jack and the guitar's bridge piece, I'm missing a ground to one of the outer lugs on the switch? Would that introduce resistance between the pickups and selector switch? I apologize for my lack of knowledge about electric circuits, usually I have the same exact parts that need to be replaced.

[Platefire]

Tako

Got excited when I seen "Airline". That was my first solid body electric and was a very good experience.
Mine was a different similar model as the one shown in the picture below. It's been gone for years and have considered buying one like it on e-bay but they are $500.00+ now, mostly +  :>)

I don't know if this makes a bit of difference with your hum situation, but I have read more than once that the pickups on these guitars like the one you have and I had are not actually humbuckers but single coils!! Even though they appear the size of humbuckers were single coils. I've never verified that by looking at an actual pickup from one of those axes but have read it from more than one source. Platefire

[G._Hoffman]

Any chance of a picture of the work you've done?  It sure does sound like a ground problem.


Gabriel

[Platefire]

OK the info on the so called Humbuckers came from Eastwood who is making RI/copies of those guitars.
Here is what they say at the Link:

http://www.eastwoodguitars.com/airline-vintage-voiced-single-coil-pickups-set/

Regarding trouble shooting hum issues. I usually take the cover off the electronics, hook it up live to an amp
and try jumper wires with alligator clips on each end to jump across existing ground wires to find the problem.
Last ground problem I had the ground to bridge had broke inside the wire insulation, undetectable visually but when I jumped over it, hum quit. Also continuity checks with multi-meter to find shorted connections. The problem is their and probably very simple solution, just have to be persistent to find it. Platefire

BTW-One last thought, if you live in a house constructed prior the electrical code requiring a separate ground wire that has only a hot and neutral, that can make your amp hum but it's actually the amp, not the guitar. That's why they had the polarity switches in the old days.If it is, you can actually help those old receptacles by hooking up a false ground by running a jumper wire from the ground to the neutral. On those old out of code wiring systems, the neutral is grounded at the power panel---so before doing this you would need to get someone with electrical experience to verify existing conditions before modding your house receptacles, if you did have this situation.   

[jjasilli]

+1 to platefire.  I one fixed a hum issue by jumpering from a metal pu cover to ground.  Then soldered a permanent lead.  Also check out guitarnuts.com 》grounding.  You may have a ground loop- too many grounding points.  You may also benefit from separating signal from chassis ground.

[Platefire]

Good! Glad you found it. I've been tempted to buy an old Airline like my original back in the 60's and pair it with my Silvertone 1482 amp which is a duplicate of my first amp. That was my first experience with tube breakup but I had no idea what was happening back then--I just knew something was sounding good! Platefire