Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shaun on February 19, 2020, 03:19:24 pm

Title: HiFi output tranny with screen windings
Post by: shaun on February 19, 2020, 03:19:24 pm

I have an old output tranny from a Bonnet Box record player (circa 1960). The amp was akin to an AC30 (4 * EL84s and an EF86 pre, 12ax7 PI).

It has two output taps, but it also has four primary taps, or at least it seems that way. Two leads went to the EL84 plates, and two went to the 9 pins - the tubes were paired. So it seems the design used AC from the transformer to balance the screen grid to the plates. I just wondered if anyone knew anything about how these worked, as I'd like to try the transformer in a build sometime.

Cheers.

Title: Re: HiFi output tranny with screen windings
Post by: sluckey on February 19, 2020, 03:26:17 pm

Search for ultra linear (UL). Plenty of info about UL. You can also use that OT in a standard PP circuit by just taping off the screen taps and connecting the screens as usual.

Title: Re: HiFi output tranny with screen windings
Post by: shaun on February 19, 2020, 03:39:23 pm

Thanks Sluckey. I'll do the research.

Title: Re: HiFi output tranny with screen windings
Post by: jjasilli on February 19, 2020, 03:43:36 pm

http://el34world.com/Forum/index.php?topic=24834.0 (http://el34world.com/Forum/index.php?topic=24834.0)