Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on December 02, 2022, 04:23:39 pm

Title: Everyday I discover something new (to me) - Selmer 25U Phase Inverter ???
Post by: kagliostro on December 02, 2022, 04:23:39 pm

I had under the eyes lot of times the Selmer schematics and always in my mind the PI in the T2U and 25U were archived as Transformer Phase Inverters

few minutes ago I was astonished seeng that the PI isn't a transformer, in the schematic it is indicated as a coil with an intake (50% I think)

Can someone explain how that can act as a PI ?

There are other amps with this architecture ?

Is possible to find documentation about those kind of coils ?

(https://i.imgur.com/R7M4Uew.jpg)

(https://i.imgur.com/J1NRV6N.jpg)


Many Thanks

Franco

Title: Re: Everyday I discover something new (to me) - Selmer 25U Phase Inverter ???
Post by: sluckey on December 02, 2022, 05:11:54 pm

The coil is an autotransformer.

Title: Re: Everyday I discover something new (to me) - Selmer 25U Phase Inverter ???
Post by: PRR on December 02, 2022, 06:01:48 pm

Specifically a Center-Tapped autotransformer.

You can fake it with a high-impedance push-pull transformer primary.

Radiotron Designers Handbook 4th, page 522. (I think the text in (C) is wrong.)

Title: Re: Everyday I discover something new (to me) - Selmer 25U Phase Inverter ???
Post by: kagliostro on December 02, 2022, 06:27:10 pm

Many Thanks Sluckey & PRR

(https://i.imgur.com/hDG7noH.jpg)

Franco