Ran into an odd situation with ALL my amps

[Denis]

I recently shuffled two rooms around so  now all my amps are in the same room. They are at the far end of the room while my desk is at the other next to a tall lamp.
Well, the other night my solid state Fender Bassman 10 combo was humming a little bit and when I moved towards the desk, the hum noticeably got worse. It stopped as soon as I put my fingers on the strings and dwindled when I went towards the amp.

Thinking the cable was wonky I changed it out for another. Same thing. Tried it with another bass and the same thing happened. Then I switched the cable back to the original. Same thing.

All the basses I tried had round wounds on it so I tried one of my Bachs with flats. It was noticeably quieter but it was still there.

Getting really curious about it, I turned the amp to face the wall but the sound got worse as I went towards the desk. Then, I thought maybe the wall outlet was weird so I ran an extension cord from the kitchen. No dice, same thing.

So, I thought, "Hmm, maybe something in the solid stateness was weird. So, I pulled out the Sunn 200S, and all tube head, sitting on the 4x12 cabinet. SAME THING!

Perplexed, I turned the lamp off, turned on the ceiling light, and sat down at the desk. The Sunn was dead quiet.

I switched lamps and OILA! Nothing!

Turns out the first lamp has a slider which allows you to dim or brighten the lamp as desired. The slider must operate like a transformer and was creating interference with the bass as soon as the bass came near it.

Odd and interesting but I figured it out.

[Spiritbass]

Glad you figured it out on your own. Any dimmer will literally radiate 60cycle hum quite effectively!

[Dave W]

I've run into the same thing.

[Pilgrim]

Dimmers are a notorious source of RF.  Normally one of the first places to look for that kind of interference.  Well done to find it!

[Highlander]

Dudalup, dudalup, dudalup syndrome... the infamous mobile left on in the studio...

[Pilgrim]

Dimmers....
Fluorescent lights...
Transformers (including those in tube amps)....
Transmitting equipment (DUH).....

And you never know...at my old home out in the country, there was a 5,000 watt regional AM station (KWSU for Mark) at 1250; the transmitter was about 10 miles away over a hill, but when I plugged my coily cord into my '63 P and the bass input on my blackface Bassman, I often picked up the program which was live at that time.  It was faint, but I could hear it.

RF plays many tricks.  There's a 50KW radio station transmitter in Spokane, WA (KGA).  The transmitter is near a grade school built in the 70's.  I understand that the guys working on the steel framing of the grade school had to ground their tools or they'd sometimes get sparks when tightening bolts on the steel frame members.  

[rahock]

My basement is pretty well set up. All instruments and PA are on a seperate 25 amp circuit, florescent lighting and dimmers are on a seperate circuit and a ceiling fan in a bedroom on yet another circuit. Most of the time everything is just fine with no interference, but once in a while the dimmers get to mucking things up and sometimes I get a click through the PA when the ceiling fan goes on . Again, most of the time I'm good , but once in a while things get weird.
Rick

[Highlander]

When I first picked up my Hiwatt she would pick up police-band radio - changed the valves and silence...

[Psycho Bass Guy]

Preamp tubes are way higher impedance that transistors and more prone to conducting RF because of it.