Why won't this power scaler circuit work?

[mac dillard]

The Mosfet as supplied by Dana Hall is an NTE NTE2973. I have it in my hand. The drawing from him that I have for the installation in the 18watt lite IIB circuit shows the Mosfet as a NTE2377. He probably used both.. The drawing shows the diode to be 12 volt 1 watt. I am not able to read the printing on the diode itself..Maybe tomorrow when I can get it under a big magnifier. Hope this helps.

[J M Fahey]

a) Both. 0.4v in one direction, 0.5v in the other out of circuit on diode mode.

b) In series with a 1K resistor on a power supply, it measures 6.1v across itself.

Itīs either a) or b).

[Randall]

Juan, you know more about this than I ever will, so I submit the following evidence.


in diode mode in one direction


in diode mode in the other direction


voltage measured across zener in series with a 1K resistor


32.9 volts power source

Am I doing something wrong?

[Randall]

This looks to be exactly what I am dealing with, even the layout is pretty close. The mosfet isn't named, but it is a 12v 1 watt zener, so steady as she goes. I will install the 12v when I get it, and we shall see. And shame on Morgan for not disclosing parts on an obviously pirated circuit.

http://www.ampmaker.com/infocentre/thread-152.html

[alexradium]

The guy is too busy with the PlayStation,seriously,I'm not joking

[J M Fahey]

Juan, you know more about this than I ever will, so I submit the following evidence.

[ATTACH=CONFIG]54829[/ATTACH]
in diode mode in one direction

[ATTACH=CONFIG]54830[/ATTACH]
in diode mode in the other direction

[ATTACH=CONFIG]54831[/ATTACH]
voltage measured across zener in series with a 1K resistor

[ATTACH=CONFIG]54832[/ATTACH]
32.9 volts power source

Am I doing something wrong?

Maybe, maybe not, so far contradicting data.

To beging with I find it very confusing/annoying that BOTH your probes are RED

Whatīs wrong with BLACK common and RED hot/measuring.

I see all kinds of possible problems and even accidents just because of that.

And I see the readings, which I still find incompatible/impossible which might even indicate a malfunctioning meter or anything else.

So please:

1) get a proper pair of test probes, just looking at those pictures gives me the chills.

2) get a fresh Zener, any voltage as long as your supply can "Zener" it, anything between 3V and, say, 24V or so and repeat all 3 tests: diode both ways and Zenering.

3) get a fresh standard diode, say 1N400x and repeat tests.

If anything, to get away from that Area 51 diode pulled from an Alien craft


All this with the best intention to help, of course, and finding it weird (and thatīs an understatement) that a diode drops 0.5V under 1mA to 10mA, whatever the Multimeter feeds it in Diode mode, and same diode drops 6.1V when fed
(32.8-6.1)V/1k=26.7 mA

Also I can see six probes and wires, again with confusing repeated colour going God-knows-where outside the picture, while four are needed: +/- from supply , Red/Black from multimeter, period.
Zener and resistor being soldered together.

I bet a few around are feeling quite confused, including the Dude and myself.

Again: all trying to help, of course.

[Dave H]

Also I can see six probes and wires, again with confusing repeated colour going God-knows-where outside the picture, while four are needed: +/- from supply , Red/Black from multimeter, period.
Zener and resistor being soldered together.

I bet a few around are feeling quite confused, including the Dude and myself.

Add me to the confused list.

I was assuming the right two green probes were a jumper link connecting the resistor to the zener.

[Dave H]

I am now confident saying the zener is a 1N4742A. Do I need to order another 6v one? I think this one is original. The mosfet, I don't know, and Morgan ain't saying.

1N4742A is 12V. The circuit I posted was from Ampmaker the same place as your link in post #19.
If your circuit is the same then it should be a 12V zener. A 6V one would limit the current to too low a value.

[J M Fahey]

Yes, the green crocodiles and wire are probably joining Zener and resistor.
But anything going outside the screen is a new unknown ... in an already confusing situation, so letīs simplify it


As of:

If your circuit is the same then it should be a 12V zener. A 6V one would limit the current to too low a value.

I fully agree.
The Zener is a Current Limiter/short protection .

When too much current passes through the 10 ohm resistor it clamps the MosFet Gate to Source voltage stopping any extra current.

Problem is : the cheap switching type MosFet shown is an enhancement type, meaning it needs positive GS voltage just to turn on; which is typically between 3.5 and 4V.

So we are already "losing" that, and available drop across 10 ohm resistor is Vz-3.5V (being slightly optimist).

Now

* 6.1-3.5=2.6V "available" so maximum power tubes current is 2.6V/10r=260mA ... PEAK.
Is that enough even for a 18W amp? Let alone a larger one.

No big deal if down regulating screens only ;in my eyes too little for plates and screens.

but

* 12-3.5=8.5V so 8.5V/10r=850mA ... now weīre talking.

[Randall]

I don't understand why this is confusing, it is very simple. I'm sorry that my leads are both red, but that is my reality. Can we make the leap of faith that I am capable enough to execute a forward and reverse diode measurement? If the photos are misleading, I explain it as, 32.9v power supply + to zener cathode, zener anode to 1K resistor, other end of 1K resistor to power supply -, Fluke meter across zener reads 6.1v.

[nosaj]

I don't understand why this is confusing, it is very simple. I'm sorry that my leads are both red, but that is my reality. Can we make the leap of faith that I am capable enough to execute a forward and reverse diode measurement? If the photos are misleading, I explain it as, 32.9v power supply + to zener cathode, zener anode to 1K resistor, other end of 1K resistor to power supply -, Fluke meter across zener reads 6.1v.

Nothing a black sharpie wouldn't fix.

nosaj

[J M Fahey]

Or wrapping ends in black tape.

But the doubt remains about meter or display.

The diode test function might work poorly and the voltmeter be perfect.

So please do the tests suggested in post #21, specifically:

2) get a fresh Zener, any voltage as long as your supply can "Zener" it, anything between 3V and, say, 24V or so and repeat all 3 tests: diode both ways and Zenering.

3) get a fresh standard diode, say 1N400x and repeat same 3 tests.

[The Dude]

......and finding it weird (and thatīs an understatement) that a diode drops 0.5V under 1mA to 10mA, whatever the Multimeter feeds it in Diode mode, and same diode drops 6.1V when fed
(32.8-6.1)V/1k=26.7 mA......

I bet a few around are feeling quite confused, including the Dude and myself......

You got that right! I see the pictures, but it makes no damn sense whatsoever and is theoretically impossible for the reasons you state above. Aside from the simple DVM test showing the diode is shorted, the other caveat is that it is a 12V zener and is dropping 6V in the power supply test, so it's definitely bad.

[Randall]

I don't have another zener on hand, so that will have to wait until my order arrives.

With a 1N4002 in diode meter mode, I see 0.5v one direction, 0v the other direction. With power supply + to 1K resistor, other end of 1K resistor to diode anode, diode cathode to power supply -, I get 0.7v across the diode.

[The Dude]

Your last test shows things as they should be. After racking my brains as to what the hell is going on here, I have come up with a thought. The diode is leaky as shown on the diode test with the meter. However, it must still have enough resistance to form a series voltage divider with the 1K resistor. In other words, it's acting as a resistor and not a diode any longer. For kicks, can you measure the resistance of the defective diode both ways and tell us what you get? In other words, don't measure it with the diode check function, but like you would check a resistor of unknown value.