my vintage SVT

[jlasoul]

Early 70's head, recently serviced. Sounds awesome BUT it's noisy.
Noisy in that when you turn it up, the hum that comes through the cab is pretty loud. I don't think it's a grounding problem.
Does anyone know the likely scenario here? Thanks.

[BassIan]

What makes you think it's not a grounding problem? Can you take it back to where you had it serviced? That much noise isn't normal, and it shouldn't behave that way just after service.

Also, make sure you've done the "dummy-check" items. Is your instrument cable good? Does your bass create hum in other amps? Are there nearby electrical noise sources (fluorescent lights, etc)?

[BassmanPaul]

If you paid for the service take it back to the tech and discuss the problem with him. The amp could simply have a bad tube or could need a recap.

[BassmanPaul]

The steps that the good BassIan suggested are excellent preliminary steps. If the hum is there with nothing in the input jack then the amp needs some TLC. If it is not then That TLC should be applied to your cabling and bass.

Just as a thought, if you are standing too close to your amp, your bass will certainly pick up induced noise from the amps PT. This is quite normal. Interestingly, when I play, i stand right next to my power amp. Since I changed it out to a Class D with a SMPS I no longer get any induced noise.

[funkateer86]

^^^^^ Everything above is great advice. I've got a '71 that needs a recap. Those old-school paper caps have had 35-40 years of hard work and they will usually need replaced.