There is a way to have a negative voltage here ?

[kagliostro]

Using a PS like the one on this old Philips PA

There is a way to obtain a negative voltage (say -150v in this arrangement) adding parts to this PS ?

Many Thanks

Franco

[shooter]

need more information
will the -150 be referenced to the amps ground?
are you using the amp AND want -150?
or
do you just need -150 for something other than the amp?

[kagliostro]

Ciao Shooter

The amp is not yet existing, more, the plan of the amp is not yet existing


The circuit you can see attached is a proposal and the use will be between a preamp and the Power Tube of an SE Power Section, in the middle between the two


it was only an idea that was abandoned because of the necessity of the negative voltage


But as I'm curious I opened this thread as to know if it will be feasible to obtain such a negative voltage starting from that kind of PS


The Philips PA used 150v and 300v, the idea used the same PS but starting to from a bit higher AC voltages to arrive to have 200v and 400v


Franco

[AmberB]

Bogan PA amps derive their negative bias voltage from the B+ winding, they don't have a bias tap on the secondary.  They use a .22 uf capacitor to tap off the B+ winding, and then the circuit for the negative bias voltage.  There's no reason you couldn't do that to get negative 150 volts.

[PRR]

Bogen did it, as Amber says. I've always been afraid of doing it wrong. (Well, actually, Bogen used the 2-diode doubler, not the center-tap bridge.)

A heater transformer, backward, is simple and harder to do wrong.

[kagliostro]

Thanks AmberB & PRR

The preferred solution will be to take the negative voltage via a cap from the HT winding

but the unusual way of the PS that feed G2 using the CT put on me doubts about the feasibility

to add a small Transformer will give a more sure result but as it is a new project and at the moment there isn't a PT suitable, may be it will be ordered custom so with a dedicated winding

Franco

Franco