full wave bridge rectifier/lowering voltage

[phsyconoodler]

Is it OK to put a resistor where you run a full wave bridge to ground to drop the voltage a bit? I do it with center taps and it works.  Not sure about a full wave brodge

[DummyLoad]

yes. inefficient method though.


--pete

[phsyconoodler]

How is it inefficient?

[jojokeo]

There's going to be a voltage drop across that resistor depending on it's value and current will also be spent/wasted through this path to ground.

[DummyLoad]

current draw through the dropping resistor will be equal to that of the TOTAL load.

you have 450V supply. you need 400V at 100mA at idle. you want to shave off 50V. you add some resistor to (-) of bridge:

the flow through the bridge remains constant since the path to ground of the PS is through the (-) of the bridge. now you have a drop of 50V across "R" with 100mA flowing so dropping R would need to be 500 ohms. you burned off 5W and you need a 10W resistor. that's at idle. inefficient.

--pete

[PRR]

> How is it inefficient?

The Home Despot sells 8-foot lumber.

I need some 7 foot sticks.

I cut a foot off each one and throw it away.

Inefficient to grow 8 foot sticks and only use 7 foot of them.

It would be better to buy 7 foot sticks in the first place. But H-D can't stock all the strange sizes their customers think they want. Sometimes you just gotta throw-away the excess between what you want and what you have.

(True: odd scraps of lumber can be used elsewhere, for blocking or firewood.)

Sometimes (not often enough) the "excess" voltage in a tube amp can be turned to some other chore. Say you have a big amp and it pulls a pretty steady 130mA-160mA. Wire your preamp tube heaters in series and drop the power amp current through them. "Free" (from waste) DC heaters.

[jjasilli]

Are there functional or tonal implications re the location of the dropping resistor?   E.g., I put it in series: SS rectifier > inductive dropping resistor > 1st filter cap.  (BTW:  I like to believe that an inductive dropping resistor simulates the reactance of a tube rectifier).

[Fresh_Start]

Is it OK to put a resistor where you run a full wave bridge to ground to drop the voltage a bit? I do it with center taps and it works.  Not sure about a full wave brodge

Zener diode(s) works well between center tap and ground, and it doesn't add sag/compression. However, it gets difficult to find a cost effective part if you want to drop 50 volts in a high power amp.

This thread from the Archives may help, particularly last post.
http://el34world.com/Forum/index.php?topic=17595.0

This grounding essay from the Valve Wizard page 7 (268) shows something that might be useful. An extra reservoir cap and RC pi filter prior to the plate node on the power rail. Note that there are dropping resistors on both the positive and negative ends of that reservoir cap.
http://www.valvewizard.co.uk/Grounding.pdf

Cheers,
Chip