Zeners Question

[bakerlite]

Hey folks
My 5e7 is annoying me a bit as its PT is slightly over power - should be 340-0-340 but instead its 358-0-359.
Hence my B+ is a little over and I would like to lower it,
i have heard that zeners can be used on the center tap of the HT  is that right?
I found an image used by tubenit and have adjusted it to suit my center tap of my PT does it look ok?
thanks

[stingray_65]

That configuration will give you about a 30V drop.
use just 1 zener to bring it back to your desired 340V range.
not so sure 18-19V high will make much perceivable difference.

[sluckey]

That'll work. But, if the HT winding has a bias tap that shares the centertap, you'll have to put the zeners in the B+ side.

[bakerlite]

Ouch
Ok, So I cant use the red/blue 0v for my zener vdrop.

How are they connected in the B+ line?  in line of one of the HT leads? Or Tee'd into one of the HT leads to ground?

[sluckey]

Ok, So I cant use the red/blue 0v for my zener vdrop.

The red/blue is the 53vac bias tap. red/yellow is the 0v CT.

Put them between the rectifier cathode and the first filter cap. Zener cathode pointing to the tube cathode.

EDIT... You may be interested in this gadget. Everyone that tinkers with this stuff should have one. Look on page 2 of this pdf...

http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf

[bakerlite]

Thanks Sluckey you are a gentleman.

Does this mean the zeners work differently in this method of installation.

I understand that when they are connected to ground via the center tap you are changing the transformers reference point for ground on that particular winding from 0v to -30v (or whatever zener rating you choose).

With the method you suggest they are in series on the B+ line , do they simply 'consume' the 30volts of electricty and emit it as heat?

[sluckey]

The zeners work the same whether they are in the negative lead of the power supply (CT) or the positive lead of the power supply (recto cathode). When you put them in the B+ lead, they will only decrease the B+ supply and will not affect the bias supply. Just think of the zeners in the B+ side just as you would a dropping (sag) resistor. But the zener will drop a fixed amount of voltage regardless of current flow (within reasonable design parameters), whereas the sag resistor voltage drop varies depending on load current.

do they simply 'consume' the 30volts of electricty and emit it as heat?

They don't actually consume voltage. They consume power which is the product of the constant 30V 'drop' times the amount of current thru the zener. The wattage rating of the zener must safely handle this power consumption.

I still think you should seriously consider the bucking transformer. Build it in a small box (heck, even an electrical junction box) with it's own power cord and a convenience outlet and it can be used on any amp to reduce B+ by about 10%.

[tubenit]

I found an image used by tubenit

Just for clarity, I have never used a zener to drop B+. And I did not draw that schematic.  Perhaps I saw that somewhere and reposted it or maybe it was done by another forum member.

When I have needed a voltage drop, I have used a VVR by Dana Hall.

With respect, Tubenit

[bakerlite]

Humble apologies dude, I just saw the picture posted in a thread somewhere

[kagliostro]

This is not a way to use zener as to drop voltage, just only a different method

that gives you a bias voltage (when you have not a specific winding) and a way to drop a bit the B+

http://www.aikenamps.com/BackBiasing.html

K

[Tone Junkie]

So what type of zener would you use in this configuration.
Sorry for the newbie questions
Thanks Bill

[sluckey]

That depends on how much voltage you want to drop. Be aware that you cannot use a stud mounted case bolted directly to the chassis. Both leads will be hot.