need to drop 30V

[bnew63]

Are zener diodes at the transfomer ground the best way to drop B+ voltage.
I need to drop 30 volts AC before the rectifier.

Brian

[Colas LeGrippa]

VVr is the best way to go, IMHO . If you put 15 diodes in series, they won't even drop 30V.

[jjasilli]

Why do you need to drop AC before the rectifier?  Anyway this can be done with a bucking transformer (search the Forum, or re-post if needed).  More simply, 30V can readily be dropped from B+ with a power resistor after the rectifier. 

[kagliostro]

Many way to do the same thing

read here

http://www.el34world.com/Forum/index.php?topic=13075.msg122096#msg122096

Kagliostro

[stratele52]

VVr is the best way to go, IMHO . If you put 15 diodes in series, they won't even drop 30V.

Why not , pourquoi pas ? C'est la "job" des zeners. Ça dépend du voltage de tes zeners....15 diodes de 1 volts non  ça ne marcheras pas !

I used it very often 10 volts 5 watts zener for dropping voltage. A few of them will do the job. $0.45 each , it is best deal.

[cbass]

One of these http://www.electronicsurplus.com/Item/8142/MOTOROLA%20-%20Diode_%20zener_%2030V%2010W_%20-%201N2989B/

[cbass]

OR two of these
http://www.electronicsurplus.com/Item/10910/MOTOROLA%20-%20Diodes_%20zener_%2015V%2010%20watt_%20-%20SZ1193-15/

[stratele52]

I use 1N5347 B , Standard looking diode , no need to have a hole in amp chassis or heat sink. I is not  $0.45  it is $0.89 each , sorry .  Avalaible at Abra electronic corp . Big store in my area.

[RicharD]

Another perhaps better solution is to live with the higher voltage and rebias for less current which should = same watts.  I'm guessing your B+ is exceeding the rating of your filter caps which is why you want to dismiss the excess voltage ahead of the rectifier.  One other trick is to raise the center tap with a resistor and cap but this does put DC on the secondary of the PT which some frown upon.

[jjasilli]

BUT: bnew63 says he wants to drop AC voltage before the rectifier.  What is the reason for this, or is it a "red herring"???

[stratele52]

BUT: bnew63 says he wants to drop AC voltage before the rectifier.  What is the reason for this, or is it a "red herring"???

You are right . I read too fast this post when I read B+ I think zener diode. I don't know why he want a lower AC . Ok for the B + but the tube's heater will be too low. Or is power transformer has a wrong primary input ????

[bnew63]

I have an existing transformer that puts out 360-0-360
A 5E3 calls for 325-0-325.
Correct me if I'm wrong but,using a zener on the HV centre tap would only lower the B+ volts
and not effect the heater voltage.

Brian

[kagliostro]

using a zener on the HV centre tap would only lower the B+ volts
and not effect the heater voltage.

Yes

Kagliostro

[stratele52]

I have an existing transformer that puts out 360-0-360
A 5E3 calls for 325-0-325.
Correct me if I'm wrong but,using a zener on the HV centre tap would only lower the B+ volts
and not effect the heater voltage.

Brian

You just need to lower the B+ That's all.
Heater voltage are the same for any transformer, Bias voltage , you adjust it as you need.