Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bnew63 on February 16, 2012, 05:22:15 pm

Title: need to drop 30V
Post by: bnew63 on February 16, 2012, 05:22:15 pm: 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
Title: Re: need to drop 30V
Post by: Colas LeGrippa on February 16, 2012, 05:54:15 pm: VVr is the best way to go, IMHO . If you put 15 diodes in series, they won't even drop 30V.
Title: Re: need to drop 30V
Post by: jjasilli on February 16, 2012, 06:00:18 pm: 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.
Title: Re: need to drop 30V
Post by: kagliostro on February 16, 2012, 06:35:28 pm: Many way to do the same thing

read here

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

Kagliostro
Title: Re: need to drop 30V
Post by: stratele52 on February 17, 2012, 04:22:52 am: Quote from: Colas LeGrippa on February 16, 2012, 05:54:15 pm
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.
Title: Re: need to drop 30V
Post by: cbass on February 17, 2012, 07:36:09 am: One of these http://www.electronicsurplus.com/Item/8142/MOTOROLA%20-%20Diode_%20zener_%2030V%2010W_%20-%201N2989B/ (http://www.electronicsurplus.com/Item/8142/MOTOROLA%20-%20Diode_%20zener_%2030V%2010W_%20-%201N2989B/)
Title: Re: need to drop 30V
Post by: cbass on February 17, 2012, 07:49:43 am: OR two of these
http://www.electronicsurplus.com/Item/10910/MOTOROLA%20-%20Diodes_%20zener_%2015V%2010%20watt_%20-%20SZ1193-15/ (http://www.electronicsurplus.com/Item/10910/MOTOROLA%20-%20Diodes_%20zener_%2015V%2010%20watt_%20-%20SZ1193-15/)
Title: Re: need to drop 30V
Post by: stratele52 on February 17, 2012, 08:12:38 am: 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.
Title: Re: need to drop 30V
Post by: RicharD on February 17, 2012, 01:02:59 pm: 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.
Title: Re: need to drop 30V
Post by: jjasilli on February 17, 2012, 02:41:54 pm: BUT: bnew63 says he wants to drop AC voltage before the rectifier. What is the reason for this, or is it a "red herring"???
Title: Re: need to drop 30V
Post by: stratele52 on February 17, 2012, 03:29:37 pm: Quote from: jjasilli on February 17, 2012, 02:41:54 pm
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 ????
Title: Re: need to drop 30V
Post by: bnew63 on February 17, 2012, 05:35:11 pm: 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
Title: Re: need to drop 30V
Post by: kagliostro on February 17, 2012, 05:44:38 pm: Quote
using a zener on the HV centre tap would only lower the B+ volts
and not effect the heater voltage.

Yes

Kagliostro
Title: Re: need to drop 30V
Post by: stratele52 on February 18, 2012, 03:04:01 am: Quote from: bnew63 on February 17, 2012, 05:35:11 pm
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.