12000 kit HELP!!! bad noise

[clukeglue]

Hi guys,
i just purchased a metro amp 12000 kit that somebody built on the gear page. the only modification is the standby switched is flipped down for 100w pentode mode and if you flip it up it goes to triode, or some call it like a 50 watt mode. i just got the amp and i have an attenuator taking the load of it. when I'm on normal 100w mode and i dime everything, after i play a chord or note a strange heartbeat like pulsing sound goes through the speakers. is this a problem with my amp or the power in my apartment? when it pulses, the lights in the room occasionally will pulse with it.

when the amp is on triode (or 50w) mode, it does the same thing but worse because the sound gets louder and higher.

i know a lot about guitars but barley anything about amps. amp problem? power problem? load box problem? thanks guys

[clukeglue]

hey guys i did some research and it seems like this problem is called motorboating. what is this caused by and how do i fix it. is this the fault of the guy who built and sold me the amp?

[clukeglue]

wait I'm wrong sorry........
i just heard a video of motor boating. it doesn't sound quite like that. its more of a pulsing heartbeat less of a constant rattle.

[neikeel]

Sounds very odd!

Mains hum or noise from fluorescent lights is quite common.

First suggestion is to try another venue then report back.

How is it at lower volumes or just directly into speakers?