Ampeg V-4B Reissue Hum

The input jack likely shorts to ground with nothing plugged in. If you've got no noise with the gain and volume cranked and nothing in the input but you get noise with a cable plugged in then the issue is likely somewhere between your cable and the V1 tube. Could be a noisy tube, could also be induced noise from your surroundings, especially with a rick since the coils aren't hum cancelling.

 

If the amp is hum free before an instrument is plugged in, it's unlikely but not impossible the amp is the problem.

Check the outlet for a good ground. Are your pickups humbuckers or single coils. FYI single coils pick up lots of EMF. What gain and volume setting are you using when you are playing? I don't know any amps that are dead silent with gain and volume dimed. How much does the hum vary if you move around? Try a different cable.

 

Likely nothing at all wrong with your amp.

What you are hearing is noise being picked up by the unterminated cable, and then when you plug the bass in, noise picked up by the pickups. Your symptoms match this condition pretty exactly.

 

Noise with the cable plugged in, but nothing connected to the far end of the cable is entirely normal. An unterminated cable will pick up noise (electromagnetic fields) in the surroundings.

Because there is no noise without a cable, the jack shorts the input, it's almost certainly not the amp or the V1 tube.

 

had same problem...get a Furman power conditioner online at Reverb or Ebay,,,it kills all interference..you'll be happy you got one

 

A power ‘conditioner’ is nothing more than a glorified power strip. It will not affect the background hum from an amplifier.

 

Some hum is normal from pretty much any AC powered device. If you stand too close to the amp you will hear more hum as the instrument's pickups will react to the stray magnetic fields emanating from the power transformer.