el34 pp cathode bias amp clip and Power supply // earth ground question

[rexindigo]

Hi there,
1.) this is a very basic question and I apologize for it:
- building my last amps i used classic PTs and connected the mains earth to the chassis and there i also connected the ground coming from my full bridge diode rectifier and therefore the ground of the whole circuit
- now I am about to build a power supply with a 12 Volt ac wall wart and a 12 to 230 Volt transformer. (12 Volt for the filaments and the stepped up 230 Volt for the B+)
- there is only 2 AC cords coming from the wall wart , no way to earth-ground the chassis.
- if i connect the bridge rectifier ground to the chassis, will this mean there is say 290 volt on the chassis?
- thanks for any comments

2.) As i am a plague to this forum with my stupid questions i though it might be a little releave to give you a small clip recorded with my final version of the EL34 PP Amp i worked on since february. I totally rebuild it at last, with cathode bias and a second tube/diode clipper channel, so have fun with it and be forgiving to all my silly questions ;-)

[rexindigo]

no suggestions to my power supply question?

[MattT]

I can't really answer your question but I wanted to bring up the issue of current and that 12vac wall wart. Are you sure the wall wart can handle all that current?

[loudthud]

The simple answer to your question is no, there won't be 290V on your chassis. But there will leakage current from the wall wart that may give you a tingle (mild electrical shock) if you touch the chassis and an earth ground. This is a safety issue and may violate rules in your country. You should research your country's safety rules or find a wall wart that provides a ground. A similar method is used by Hoffman in one of his projects.

http://www.el34world.com/projects/tube_box.htm

[MWJB]

Aren't wall warts typically isolated from the mains via their transformer, hence you only need the 2 wires? Otherwise we'd all be getting zapped by delays & tubescreamers?

If wall warts had a mains ground we'd all get ground loop hum from them too.

Wall warts in the EU still only have 2 conductors, + & -.

[rexindigo]

Thank you for your replies:
@mattT: its a single tube design with a pcl86 which is a triode and a power pentode in a single envelope, the step up transfomer has 500 mA that will be enough for the plate current) the wall wart has 5 A so thats more than enough for the heater
@MWJB: my intention was that if i build up a high voltage and ground it to the chassis, this voltage would leak through my hand or guitar cabel to ground.
therefor i am now thinking of isolating the whole circuit from the chassis.
iam not afraid of the 12 volt but of the 290volt dc i create out of it
@louthud: i think i'll just build it and then measure the voltage on the chassis to mains earth.
thank you for your help!