hifi amp, tremolo-like distortion @ volume

[wall_of_sleep]

I have a small vintage hifi amlifier that is breaking into tremolo-like distortion at volume. Dialing up either the volume or the bass affects the rate and severity of the distortion.

The amp works great to about 75%, so I don't want to tear into it without a better idea of what the cause may be. Thanks.

 

[diagrammatiks]

it's motorboating. inadequate power supply decoupling.

 

[pdf64]

Yes, the vintage electrolytic caps are likely to be unfit for purpose.
Time to replace all electrolytics.
Pete.

 

[SatelliteAmps]

Most often the electrolytics in the preamp section.

 

[wall_of_sleep]

Thanks all. I had already swapped the filters and a couple others. Will look into completing the cap job.

 

[wall_of_sleep]

I completed a full cap job on this amplifier and am still getting the motor boating on the magnetic jack channel at around 50% volume. There is also some hum that goes off and on with pressure on the 6sc7.

Will continue troubleshooting, but am welcome to any suggestions.