Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 01, 2011, 01:38:51 pm

Title: Power Supply - a new question
Post by: kagliostro on January 01, 2011, 01:38:51 pm

Today I was reading some old treads here into the forum

here is the thread

http://www.el34world.com/Forum/index.php?topic=9564.msg86813#msg86813

I wrote

Quote

what about to put a (little enough small) transformer connected between the CT and ground as to decrease the voltage

I think that I was really wrong on that assumption

if is possible to go up or down in voltage using a second transformer

like they explain here

http://www.geofex.com/Article_Folders/vintvolt/vintvolt.htm

I doubt it will be possible to do the same putting the secondary of a second transformer in series with the CT of the PT, because of the phase change, or I'm wrong now and it is possible ??

I'm confused, can you help ?

Thanks

Kagliostro

Title: Re: Power Supply - a new question
Post by: kagliostro on January 01, 2011, 02:13:19 pm

Other two options

One will be the right one ??

Kagliostro

Title: Re: Power Supply - a new question
Post by: Tiny_Daddy on January 01, 2011, 02:16:18 pm

Easiest thing to do: run the second transformer to a bridge rectifier. Then connect the output from the bridge to the center tap of the main transformer to add or subtract DC voltage.

Title: Re: Power Supply - a new question
Post by: PRR on January 01, 2011, 05:52:59 pm

(http://www.el34world.com/Forum/index.php?action=dlattach;topic=10784.0;attach=21128;image)
Dead short across small transformer.


(http://www.el34world.com/Forum/index.php?action=dlattach;topic=10784.0;attach=21124;image)
Decreases one side, but increases the other side. Result is higher peak DC and more ripple.


(http://www.el34world.com/Forum/index.php?action=dlattach;topic=10784.0;attach=21126;image)
Works _IF_ you can get the many windings in correct phase, and the small winding is insulated for the high voltage.


For your specific example:

1) 330V to 300V is a small drop. In many cases you could just live with the higher voltage or drop it with a power resistor.

2) If there is ONLY the one secondary, you could use a small 220V:22V transformer to drop the 220V line to 198V and reduce the secondary voltages.

Title: Re: Power Supply - a new question
Post by: kagliostro on January 02, 2011, 05:13:59 am

Many Thanks PRR & Tiny_Daddy

PRR

AC reduction 03

Quote

Dead short across small transformer

so that way is not possible to have the two transformers in counterfhase

the drop of 30v was only an example

Tiny_Daddy

???

something like this ?

Kagliostro