Polytone minibrute iv noise

[JeffGGG]

I have an old (20+ years) minibrute iv. This amp has set unused for several years and when powered up, works ok but as you turn up volume or treble there is a very noticeable background noise that comes with it. Replace rectifiers? Anything else that would likely be causing this?

[Ronsonic]

What sort of noise? Normal gain rush SSSSHHHHHHH? Hum? Noise when moving the control?

Are the input jacks shorting?

In any case, I would start with cleaning all external in/out jax and all the internal conx.

[JeffGGG]

Type of noise

I would call the noise normal gain rush. It happens with out any instrument being plugged in. It is not related to moving a pot but increases as you increase the gain.

This amp has sat unused for a few years, so I'm wondering if that has any impact. I will clean the conx.

Thanks

[gbono]

I just repaired two mini brutes - a tiny mini and a mini brute all circa 1979-80. These amps are remarkably quiet at idle. Not sure what the design difference is with the IV but you might have issue with some of the input OP amps. They can be degraded by ESD and start to get noisy. If you can find a replacement part you might try swapping out the first stage op amp