Problem Lowering B+ with zenner

[gepposound]

I built a plexi 50w using the metroamp kit layout, but using as power transformer the classic tone 40-18054.
The B+ is about 465v-470v, and it's a bit high than the metroamp kit requirements .
So i tried to lowering the voltage a bit connecting a zenner diode between the HT CT of the transformer and the ground.
The problem is that the voltage don't drop ....I'm using a chassis mount 17v 50w zenner diode cathode-to-case
connection ...
Can someone tell me where I'm wrong ?

[adam10603]

asdf

[gepposound]

Thanks , in fact i care more about the screen voltage that is only 5v lower than Plate.
Most of the modern tubes can haldle over 600v on plates , but are limited on screen ...
Only the SED winged "c" can handle safely up 500v on screen ..
What i can do to be in a "Safe" voltage range ?

[Carbia]

Did you measure the voltage with or without tubes?

The Metro tutorial talks about measuring without tubes, but you have to measure it with tubes, because the voltage drops with the tubes.

[gepposound]

Yes , i measured the voltage with all tubes in.
In fact i found that a part of the problem is related to the wall voltage , that is in Europe more close to 230v than 220v.
So i resolved using the primary 240v tap , and i get 440v B+ and 6.2v on the heaters......with the 220v tap the heater voltage rise to 6.7v .

[Carbia]

yeah... the same voltage issue as always...

Usually, amps have 220v and 240v tap, but europe is running, mostly, at 230v...