what zener to use to drop 30v

[J Rindt]

Do I have to calculate some type of current that the Zeners will see.?
I need to drop about 30 Volts in this circuit. The field coil is gone, replaced with a regular speaker.
Thanks
http://f1.grp.yahoofs.com/v1/QBXGTXTuJF6Q-MFjhkvW88j4_7y-dBouWuAaw6kcOJvUA42_02XsguHCOrPV0Uw-LsI_vjxZtKUq87_gYTO3MmypvMY-DQbRFIA6Tc2ByV4/Schematics/Magnatone%20M-192-5.gif

It would be awesome if one of you guys that have graphics/computer skills, could get this info visible. I appreciate how much effort that might take, and I wish I had the knowledge/software to do it myself. But if some of these PS Voltage Dropping techniques could be preserved in schematic/lay-out form, it would be a huge assistance for future builds, builders, discussions.
Thank You

This is what I have done.

The zeners can be a combination of 10v, 14v 18v (or whatever value you wish) to acheive the desired voltage drop. The zeners shown give an approximate 50v reduction.

[tubeswell]

Do I have to calculate some type of current that the Zeners will see.?
I need to drop about 30 Volts in this circuit. The field coil is gone, replaced with a regular speaker.
Thanks
http://f1.grp.yahoofs.com/v1/QBXGTXTuJF6Q-MFjhkvW88j4_7y-dBouWuAaw6kcOJvUA42_02XsguHCOrPV0Uw-LsI_vjxZtKUq87_gYTO3MmypvMY-DQbRFIA6Tc2ByV4/Schematics/Magnatone%20M-192-5.gif

It would be awesome if one of you guys that have graphics/computer skills, could get this info visible. I appreciate how much effort that might take, and I wish I had the knowledge/software to do it myself. But if some of these PS Voltage Dropping techniques could be preserved in schematic/lay-out form, it would be a huge assistance for future builds, builders, discussions.
Thank You

This is what I have done.

The zeners can be a combination of 10v, 14v 18v (or whatever value you wish) to acheive the desired voltage drop. The zeners shown give an approximate 50v reduction.

On a High Tension winding you can bank on about 80-100mA for an amp with a pair of  6V6s or about 140-180mA for an amp with a pair of 6L6s. Use 5W axial zener(s) mounted on a tag strip reversed-baised (cathode/banded end pointing to ground). For a FW rectifier, put the zener(s) to ground in series with the High Tension centre tap. For a bridge rectifier, put the zener(s) to ground in series with the ground side of the rectifier. For a 30V drop, use either 2 x 15V, or 3 x 9V, or 2 x 9V and a 12V or some such (all in series).

[J Rindt]

Thank You So Much........

[kagliostro]

Is this another way to solve the problem ??

(about schematic I've read there are mistake on pin connections in the schematic)

http://spinoo.free.fr/projetG5/charpy/Zener2.pdf

Kagliostro

[Tone Junkie]

Ok I finally found the one I was looking for.
Thanks Bill

[RobBozic]

I've used the circuit on the left to drop about 50V.

Apologies if someone's already posted this, I couldn't be bothered reading through the whole thread.

Rob

[xm52]

In some applications you can use a tube, such as a 12AX4GT to drop the 30 volts. This is a really neat half wave rectifier tube. Connect the cathode to the HV center tap, the plate to ground through a fuse, and the heater voltage.

The advantage is slow turn on and a built in voltage drop.

[Fresh_Start]

I've used the circuit on the left to drop about 50V.

Apologies if someone's already posted this, I couldn't be bothered reading through the whole thread.

Rob

Rob - Thanks for that Aiken sheet.

Chip

[Tone Junkie]

Someone up top was looking for this.          Bump   
Bill

[Tone Junkie]

Found this one Geezer sent me when I was looking for it.
Didnt we also have another discussion on this were someone put the zeners in line with the B+ to drop it.
could some one find that one, I have been looking but cant seem to locate it. Im trying to put all the differant ways in my notes for future referance.
Thanks Bill

[kagliostro]

If you don't have stored it previously

here is one other method



K

[Tone Junkie]

Thanks kagliostro

[billcreller]

I just tried the "backward" filter cap and resistor trick.  It worked good. I had a pair of 680 ohm 10 w resistors, and just hooked it with those in parallel to check it out.  It went from a bit over 500 down to 318. A bit too low for what I want, but I can adjust it up. And those resistors didn't get warm......

[Tone Junkie]

Bill could you post that one.
Thanks Bill

[jazbo8]

Bill could you post that one.
Thanks Bill

It was shown on RichardD's schematic: http://www.el34world.com/Forum/index.php?action=dlattach;topic=11506.0;attach=23239;image

Jaz

[billcreller]

I dug up this old thread to review it.  When I tried to get the B+ voltage up where I wanted it, around 380 etc, from the too-low 318 volts, using lower value resistors, I noticed that the voltage before the resistor/cap combo was the same as the output side of that combo, while the voltage from the rectifier tube remained high.  SO is the rect. tube going to get "over-loaded" with this arrangement ? 
  This is some weird shit to me !!

[phsyconoodler]

I've used this before and never had an issue with loading the rectifier.It's all about the relationship with the center tap to ground.Adding the resistor doesn't necessarily add load.It does add some reverse voltage though,so that's why the filter cap gets reversed like on a bias tap.
  I don't really understand it but I do know it works just fine.

[kagliostro]

Here you can find a very good explanation and documentation about what happen adding a resistor between the CT and ground

That solution has more than a purpose

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

@ Billcreller

If you measure the voltage before and after a drop resistor as to have a difference on the measured voltage, there must be a load, if no current is going across the drop resistor no drop is produced

For this reason you must also consider that in a class A amp the current consumption is near always the same, in an AB1 circuit the current changes much more from idle to full roar, so the drop resistor acts also as a SAG resistor (in junction to the SAG effect given by the Tube Rectifier) and after the drop resistor you can measure a higher voltage at idle than at full roar

---

I noticed that the voltage before the resistor/cap combo was the same as the output side of that combo

Have you get your measures without tubes ?

K

[billcreller]

 The voltage readings were with tubes.  Also., my "field resistor" which takes place of a field coil type speaker. is getting hot, and that's not happened with all the clones I've built of this amp.

I think it's time to back off & replace the PT with the right type