Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dynaman1 on October 16, 2010, 10:44:52 am

Title: PT primary confusion
Post by: dynaman1 on October 16, 2010, 10:44:52 am

Howdy. I've a used Randall 100W power transformer that was gutted from an RGT-100. The schem can be found in Doug's library here: http://www.el34world.com/charts/Schematics/Randall_RGT-100.pdf

Unfortunately, the schem doesn't indicate the color codes or wiring for the primary side and I'm woefully ignorant to winding/phasing of a PT made like this. By applying a low voltage to the secondary side, I've isolated both "groups" and my results jive with my resistance measurements. The presence of the 100V tap makes it easy enough to figure out the "ends" of one group, but I'm not sure about the other.

I want to run this transformer for 120V operation. I'm guessing that the two groups should be wired in parallel for 120V operation and series for 240V (or 220V)? Is it a simple matter of wiring the "ends" of each winding in parallel and checking the voltages? I've a 50/50 chance of getting it right the first time.....

Thanks for any help.

Title: Re: PT primary confusion
Post by: sluckey on October 16, 2010, 10:53:20 am

There's a wiring diagram just to the right of the PT that has all the info you need.

Title: Re: PT primary confusion
Post by: dynaman1 on October 16, 2010, 10:59:03 am

Um...oops. Yeah, I think I'll just run with that info. Every time I've opened that file, I've immediately enlarged the pic to view the tranny section of the schem and completely missed that little diagram. Feel free to delete this waste of bandwidth.

Thanks so much.