Understanding load lines

[tvrgeek]

More newbe stupidity.

Re: Meng splitter, 6N2's.
I measured 108 V on the plate, .66 on the cathode. So current is .66 mA.
(227 V on the top of the 180K plate resistors. )
Looking at the load lines, this puppy is barely turned on and in serious non-linear state, if I draw line between .66mA and 108V.

It looks like to get anywhere into the slightly more linear range, one would need considerably more voltage across the tube and at least double the current. Am I reading this correctly?

If every little bit helps, then I could just replace the 22K in the B+ wiht a diode ( oft recommended anyway). Then reduce the 180 plate resistors and increase the cathode resistors. 1.5 ma looks like a better start.

[aardvarkash10]

don't forget, at 0ma current, the voltage at the anode is actually your full supply voltage...

[Richard Ellis]

If I can read Chinese correctly....which I can't..
It looks like 275 Volts at 1.75 mA will swing thru some symmetrical loadlines.
Looks like -1.0 Volts for bias...........The loadlines I found are really fuzzy & hard to read.from what I can tell is yes, your set-up is way down there & needs tweeking.
300V Max, 10mA, Max, 1W dissipation.

So??? Your Anode resistor is?? With 300V & 1.75 mA???
__________________________________________________ _____Rick.....

[tvrgeek]

Well, it does not want more than 250V, so leaving the 227, line from 1.75 ma to 225 V and I pick about 1V because it looks like about the center of the liner range. That looks like about 120V across the tube. So with 227 available, then the anode resistor would be 61K. Tweak the cathde to get the 1V. Did I do that correctly?

[Eli Duttman]

I believe that the Chinese 6N2 is the same as the Russian 6Н2П. If that's the case, just treat each section as if it were in a 12AX7/ECC83.

[rotaspec]

Originally Posted by tvrgeek

More newbe stupidity.

Re: Meng splitter, 6N2's.
I measured 108 V on the plate, .66 on the cathode. So current is .66 mA.
(227 V on the top of the 180K plate resistors. )
Looking at the load lines, this puppy is barely turned on and in serious non-linear state, if I draw line between .66mA and 108V.

It looks like to get anywhere into the slightly more linear range, one would need considerably more voltage across the tube and at least double the current. Am I reading this correctly?

If every little bit helps, then I could just replace the 22K in the B+ wiht a diode ( oft recommended anyway). Then reduce the 180 plate resistors and increase the cathode resistors. 1.5 ma looks like a better start.

Here's my beginner's take on load lines for the 6N2 in the Meng.
227v B+ with plate at 0v (maximum possible current flow) is 1.25mA with a 180k on the plate. So that is the Y point for your load line on the characteristic curve graph.
227v B+ is (as Ash said) what appears on the plate with no current flow, so that is your X point.

Now we don't want positive grid current (that's bad), so our grid can't go above 0v ref cathode. With the bias voltage you measured, that means a signal on the grid can't more than 0.66v peak (0.466v RMS) before cutoff (clip) on one peak, and positive grid current on the other peak. If you are driving this amp from a CD player, you can get peaks greater than this.
This is why I think that stage sounds not as good as it should. A re-bias will help by giving more headroom, but the whole paraphase idea is messy to my eyes, not to mention hard for a beginner to understand when the signal output from one stage affects the bias on the other (hence the balance pot).

If any of the gurus want to chime in to correct me then feel free.
More thoughts to come when my tube nube brain gets to it.

Gary

[rotaspec]

The Russian 6N2P will cope with a max of 300v Va, but I don't know about the Chinese one. I wouldn't try it unless I had spare tubes.
My experience of the Chinese 6P1 output tube is that bad things happen over 250v, whereas the Russian 6P1-EV coped well over its rated 250v limit. I didn't bother to try that with the Chinese 6N2.
Remember, bumping B+ up overall will affect the output stage as well.

I had thought about picking the driver stage plate supply from before the original B+ dropper, via a new dropper. That would give (in my case) about 310v max that I could drop from. This is something along the lines of what Ian has done with his extra voltage multiplier stage tacked on the existing doubler.
Whether this sort of fiddling will materially help the paraphase stage is unknown. I still think the cathodyne that Ian used is a better option, but he (and I concur) that it didn't sound much better when used with the 6N2 in this circuit. Happier with 6N1P, happier still with 6N1P and more B+ and idle current.
I would like to try 6N3P but it has a radically different pinout which makes life difficult on the PCB in the Meng.

[tvrgeek]

It clips at .36 V RMS input, which is 5.77 V out into 7 Ohms, or all of a whopping 4.7W. I have not looked to see which stage is failing first.

Were my calculations correct?

Eventually I do intend to do it up pretty close to Ian's design. The whole point is to learn the tube game on the way.

[rotaspec]

Originally Posted by tvrgeek

It clips at .36 V RMS input, which is 5.77 V out into 7 Ohms, or all of a whopping 4.7W. I have not looked to see which stage is failing first.

Were my calculations correct?

Eventually I do intend to do it up pretty close to Ian's design. The whole point is to learn the tube game on the way.

Calculations are right as far as I can tell. Should back up the point I mentioned on one of the threads about not trusting the power claims for Meng amps. Remember, they rate this one at 10wpc.
I'm getting close to 5W at clip out of a single EL84 on my homebuilt SE (and it sounds better). The only thing holding me back from a full EL84 conversion on the Meng is some doubt over the capability of the PT to safely supply the extra current (.25A extra heater juice per output tube over and above the increase I already have by changing the 6N2 to 6N1).
Some ventilation in the transformer cover is already being planned even if I don't change the circuit.

[Eli Duttman]

Originally Posted by rotaspec

Calculations are right as far as I can tell. Should back up the point I mentioned on one of the threads about not trusting the power claims for Meng amps. Remember, they rate this one at 10wpc.
I'm getting close to 5W at clip out of a single EL84 on my homebuilt SE (and it sounds better). The only thing holding me back from a full EL84 conversion on the Meng is some doubt over the capability of the PT to safely supply the extra current (.25A extra heater juice per output tube over and above the increase I already have by changing the 6N2 to 6N1).
Some ventilation in the transformer cover is already being planned even if I don't change the circuit.

I'm unfamiliar with the amp in question. What's the OEM O/P tube type? If you're worried about overstressing the power trafo, think about a "12" W. type other than the EL84, say the 6AQ5/EL90. Unlike the EL84, the 6AQ5 draws only 450 mA. of heater current. O/P "iron" that works with EL84s also works with 6AQ5s.