Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: wsscott on June 27, 2025, 12:26:43 pm

Title: Power Transformer CT with No Insulation
Post by: wsscott on June 27, 2025, 12:26:43 pm

This is from the 1947 Oahu Tonemaster I've been working on.  Here's a photo of the bare CT lead.

Has anyone ever seen a CT for a power transformer that's just a bare, braided wire, like this connecting to ground?

Seems weird to me.  I'm having some hum and can't figure out where its coming from.

Title: Re: Power Transformer CT with No Insulation
Post by: passaloutre on June 27, 2025, 12:39:47 pm

I’ve seen transformer frames grounded like that. Are you sure it’s the CT. I would’ve thought the yellow wire next to it was the CT.

Title: Re: Power Transformer CT with No Insulation
Post by: tubeswell on June 28, 2025, 04:37:15 am

Could be a Faraday shield grounding lead

Title: Re: Power Transformer CT with No Insulation
Post by: wsscott on June 28, 2025, 08:03:47 am

Thanks.  I've concluded it's a ground of some sort but not the CT.  It would have been nice if the wires were of different colors.

Title: Re: Power Transformer CT with No Insulation
Post by: passaloutre on June 28, 2025, 08:48:30 am

Of the wires coming out of that hole, I’d be willing to bet the black ones are primary, the twisted reddish yellow are the secondary, and the lone yellow is the center tap.