Zener diode placement

[Diverted]

 Hi all,

I am putting together a small amplifier with some parts I have lying around. Among them, the power transformer is a little different in that it was designed for a solid-state rectifier. It has no high-voltage secondary center tap. With a solid state rectifier attached, my B+ is a little north of where I want it to be so I was thinking about putting in a few Zener diodes to bring down B+ a little bit (three@12v, 5w).. With the transformer like this, that has no high-voltage secondary center tap, where would be the best place to put these diodes? I’ve never reallyused them before.
Thanks!

[sluckey]

I would put them between the FWB positive terminal and the first filter cap. Cathodes must point to the bridge.

[jjasilli]

I  think it's a buckdancer's choice: what sluckey said, or in the ground leg of the FWB.

[trobbins]

The concern about putting the zeners between rectifier and filter is that they get stressed by the high peak current, and its difficult to appreciate how much power they may dissipate, and hence you could easily cause them to fail.

If placed after the first filter, then you will know their power dissipation (VxI) and can work out how to derate them for the cooling you can provide them.  A 1W zener can't normally dissipate anywhere near 1W.

[jjasilli]

If cooling (heat) is a factor, then placing them in the FWB ground leg enables heat sinking to the chassis.

[Merlin]

If placed after the first filter, then you will know their power dissipation (VxI) and can work out how to derate them for the cooling you can provide them.  A 1W zener can't normally dissipate anywhere near 1W.

+1.