Need some help finding the problem...

[impsick]

This is really stupid but Man today i hook up this project that i've been working on, it's all laid out on breadboard. The second i flip on my variac the thing starts making a hum and vibrating. Funny thing is and it's driving me crazy, it only does this when the ground wire to my scope probe is connected. I've just about checked over this circuit 10x, checked the breadboard for the most part too. Anyone have any ideas? It's probably right under my nose but right now im getting so mad i cant think right. , you know how that goes. Anyways if any has any ideas im all ears. I think i've checked it all but l've got to be missing something.

Power sources are a variac getting rectified and to the plates, and a DC power supply to the heaters. Scope is hooked to the output w/ the scopes square wave feeding the input and a multi-meter. Thats everything connected to the circuit if thats any help.

thanks

[bob91343]

You need to isolate all of it from the power line. A variable transformer offers no isolation. You are lucky you haven't killed yourself!

[impsick]

of course that explains it, i left out my iso transformer. i'm glad you said that cause my bench is so out of order right now. time to organize. thanks Bob i knew someone would see what i wasn't.