Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on January 20, 2012, 03:33:27 pm

Title: Lowering B+
Post by: dude on January 20, 2012, 03:33:27 pm

I know there are several ways to lower B+ - Zeners, resistors, chokes, tubes etc.

I have a B+ of 454vdc, a little high for my GE gray plates for me at least, the screens have a 22K dropping R and are at 383v, OK

I'd like to get that 454v down a little, like 25v.  I know the screens will go down too but that's OK, 383 is on the high side anyway.

Would it best to use a resistor or a few 5 watt 15v Zeners in series?

Bridge rectifier, no tube and no CTR tap on the PT.

I was thinking about 5 watt, 2.7K.

al

Title: Re: Lowering B+
Post by: kagliostro on January 20, 2012, 07:08:34 pm

Big zener can be expensive

here is one way with only one little zener

(http://www.el34world.com/Forum/index.php?action=dlattach;topic=13012.0;attach=27729;image)

as you have no CT you must connect it between the negative of the bridge and ground

also you can try with a pair of big resistor between the transformer and the bridge

(http://www.el34world.com/Forum/index.php?action=dlattach;topic=13012.0;attach=27727;image)

Kagliostro

Title: Re: Lowering B+
Post by: dude on January 20, 2012, 08:00:48 pm

I don't have 15 watt 150 r so the Zener method looks good.

Can I use two 15 volt zeners (5 Watts) in series for 30v drop without making it variable?   don't have the components handy.


What is the "Tip 147" to pot and the arrows there, excuse my ignorance. I see this on some schematics

al


  

Title: Re: Lowering B+
Post by: kagliostro on January 20, 2012, 08:05:56 pm

Variable is only an option

The 15w 150R resistors where on that amp, in your amp the resistors must be calculated

the amplified zener doesn't need calculation

http://docs-europe.electrocomponents.com/webdocs/048e/0900766b8048e20a.pdf (http://docs-europe.electrocomponents.com/webdocs/048e/0900766b8048e20a.pdf)

http://it.mouser.com/ProductDetail/STMicroelectronics/TIP147/?qs=sGAEpiMZZMupZfs%2fwBb3DGpkiAxa96AGuVWL5L1RJ0Y%3d (http://it.mouser.com/ProductDetail/STMicroelectronics/TIP147/?qs=sGAEpiMZZMupZfs%2fwBb3DGpkiAxa96AGuVWL5L1RJ0Y%3d)

Tip147 € 1.38 at Mouser

Kagliostro

Title: Re: Lowering B+
Post by: dude on January 20, 2012, 08:56:05 pm

Quote from: kagliostro on January 20, 2012, 08:05:56 pm

Variable is only an option

The 15w 150R resistors where on that amp, in your amp the resistors must be calculated

the amplified zener doesn't need calculation

http://docs-europe.electrocomponents.com/webdocs/048e/0900766b8048e20a.pdf (http://docs-europe.electrocomponents.com/webdocs/048e/0900766b8048e20a.pdf)

http://it.mouser.com/ProductDetail/STMicroelectronics/TIP147/?qs=sGAEpiMZZMupZfs%2fwBb3DGpkiAxa96AGuVWL5L1RJ0Y%3d (http://it.mouser.com/ProductDetail/STMicroelectronics/TIP147/?qs=sGAEpiMZZMupZfs%2fwBb3DGpkiAxa96AGuVWL5L1RJ0Y%3d)

Tip147 € 1.38 at Mouser

Kagliostro

Thank you, same principle as Hall's Amplification

http://www.hallamplification.com/main.html?src=%2F#2,2 (http://www.hallamplification.com/main.html?src=%2F#2,2)

I only had 15v 5W Zeners so I put them in series off the negative side of the bridge to ground, dropped my B+ by 30v

Good enough for me at this point, the Halls' VVR lets you drop the voltage by a couple hundred volts, I guess if you want to really lower the output of the amp but the Mosfet they use is $12, lot more than $1.38.

Thanks,

al

Title: Re: Lowering B+
Post by: stratele52 on January 21, 2012, 05:03:49 am

I use often few 10 volts 5 watts zener with success. There are not expensive

Title: Re: Lowering B+
Post by: jjasilli on January 21, 2012, 12:46:05 pm

My personal preference would be a dropping resistor.  Second choice, if there's room, a CT 12V bucking tranny -- a 6 or 12V drop in AC wall supply should work out ok.

Title: Re: Lowering B+
Post by: stratele52 on January 21, 2012, 02:18:24 pm

Quote from: jjasilli on January 21, 2012, 12:46:05 pm

My personal preference would be a dropping resistor.  Second choice, if there's room, a CT 12V bucking tranny -- a 6 or 12V drop in AC wall supply should work out ok.

Dropping resistor will give ( to much ) sag.

A c.t 12 volts bucking tranny  ? ? More equipment on AC line outlet ! Not for me.