5150 III noise problem

[hthomas]

So I have a 5150 III. Im trying to figure out if I have a noise problem. I had the amp on, with the guitar cable not plugged in. on the 2x12 speaker was plugged in. it makes a hizzy type sound on all 3 channels. is that just the amp being on? or should it be completely quiet?

I was curious so i unplugged the speaker cab and the noise went away. i thought it was speaker cables then so I changed cables and it still happened. any ideas?

 

[MYLILSS]

i know these amps have issues with blowing preamp tubes but not sure if this would be causing that. you might take a look at your preamp tubes

 

[hthomas]

what should I look for?

 

[nevusofota]

what should I look for?

I would agree with it possibly being a preamp tube. My amp is extremely quiet. Preamp tubes have been an issue with mine recently. If the noise is on all three channels than you would want to replace certain preamp tubes individually. The preamp tubes to replace first are V1 (serves all three channels) and V8 (inverter). There is a diagram on the left inside wall of the amp to show you where these tubes are located.

 

[Bishop5150]

I've noticed since I changed the preamp tubes on mine I've been able to turn my noise gate almost completely off. It seems to be much quieter.

 

[Marshall Law]

I was curious so i unplugged the speaker cab and the noise went away.

Don't ever do that again, or you may be replacing a output transformer

 

[Bishop5150]

I was curious so i unplugged the speaker cab and the noise went away.

Don't ever do that again, or you may be replacing a output transformer

+1000