ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

zener diode

:

6/16/1999 9:45 PM
Randy	zener diode What is the correct way to hook up a zenor diode to lower plate voltages? Randy

6/17/1999 6:49 AM

Bruce/ Mission Amps

If you mean as easiest...

If your (PT), power transformer, has a center tap to ground in the middle of it's high voltage secondary, then insert the zener with it's cathode band to ground and the anode connected to the center tap wire.

This will effect the bias supply voltage, if it also uses the center tap as a reference, so be prepaired to make some adjustments.

If it is a self biased amp then the thing will probaly be OK.

If your feeling froggy, you can try the zener diodes (also with the cathode bands pointing towards the center tap) in series with the high voltage DC line. Works, but is scarey.

I prefer to use the zener on the center tap myself.

Bruce

6/17/1999 8:42 PM
Randy	Thanks Bruce, that's what I thought. Is the rating of the diode the amount the voltage will be decreased? Randy

6/18/1999 8:10 AM

No it's supposed to be but never is.

If I want to drop say, abt 20v, I will use two 12v 5 watt zeners in series.

The darn things drop voltage differently when there is current flowing and I don't know why they should do that when they are rated at much more current then what we are drawing through them. Another topic I guess.

For a SS rectifier power supply, I sometimes include a 75-135 ohm 10 watt wire wound resistor in series with the zeners to give it a little cush. Sorta tubey.

BTW:

Dropping 24v@ 200ma is 4.8 watts... divided into 2 zeners so each is loaded down by 2.4 watts. They get pretty warm!

Use that as a loose model to determine how many 5 watt zeners you need to safely handle the volts you want to loose.

50 watters are kinda pricey at $12.00 to $15.00 each.

5 watters are less then a dollar here in Denver, CO.

Bruce

Mission Amps

6/28/1999 4:25 PM
MKB	Hi, Bruce. Is it possible to parallel identical zeners, with perhaps a small value resistor in series with each one to balance them? My intuition and several engineers I have talked to say no. However, I have some 100V 5W zeners and I need a 100V 10W, I'd love to find a way to use what I have. Thanks!

6/17/1999 11:45 PM

Randy, I Just did this mod a couple of days ago on a Blackface Deluxe Reverb. I used a NTE 5270AK Zener Diode

36v 5% 50wt DO5 (Cathode to case) type. A (ECG5270AK) replacement. $22.50 from Charles @ SwampAmp. The voltages

were real hot for this amp 462VDC on the plates. The amp

was going thru tubes often... It also had a poorly done mod of a Solid State Rectifier installed instead of the Rectifier tube. When I removed the SS rectifier it reduced the voltage from 462v to 418v (5Y3 Rectifier tube)and when

I installed the Zener it brought the voltage down to 405VDC.

Now the guy can run just about any tubes. I did change the bias pot resistor from a 10K to a 5.6K to get the bias in the range I needed. Email me for the installation, its kinda of lenghtly.

Tony

Nashville,TN

6/28/1999 10:19 AM
paul perry	You can make higher voltage zeners by stacking them in series, like to get a 35v 25w zener you can use five 7 volt 5 watt ones. These are $8 for a set of 10 at DigiKey. (actually 6.8v nominal, but there will be a little more drop at full current).

Page 1 of 1