How about comparing the role of tran-sconductance in screen voltage regulation in a simple series resistor or wire to a diode, ( and zener) in series? Because the 2 are completely different, therefore the trans-conductance action result for screen dissipation is not exact the same.
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For a proper operation as pentodes, screen grid must be at cathode AC potential, independently of the DC biasing point choose. In other case, its behavior will be more or less triode with mix of pentode, but not true pentode operation.
Screen dissipation arises from the product of screen voltage and screen current. Transconductance has nothing to do with this.Koonw said:
To get low distortion amplification, the screen either has to be fixed in voltage with respect to the cathode (pentode mode) or fixed with respect to the anode (triode mode). A smallish resistor is acceptable, and brings other benefits.
A diode either does nothing if it remains forward biased, or disconnects the screen if it ever becomes reverse biased. It is just possible that a forward biased diode could have enough dynamic impedance to act as a screen stopper and so prevent parasitic oscillation, but a resistor or lossy choke will probably do a better job.
Dave, respectfully, I believe it is fruitless to continue explaining how useless is the diode: when a stupid thing becomes popular, then there is nothing to do.
The screen voltage on G2 determined the transconductance, if you have a different Vg2 be it 100v, 150v, 200v or 250v..transconductance would be all different. You also need the correct Eg2 datasheet.
Vg2 is never identical, if component or value that is used to derive the Vg2 are different, they need to become stabilised.. taking all into account, what if one results in Vg2 250v, the other just 150v, how does this come about?
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I invented LED in screen grid, but did not patent it, so everyone can use it for free.
The LED in parallel with resistor.
It flashes on a LDR in an input attenuator.
The result is, a smart compressor-limiter that knows when the amp starts clipping and disallows that.
The LED in parallel with resistor.
It flashes on a LDR in an input attenuator.
The result is, a smart compressor-limiter that knows when the amp starts clipping and disallows that.
But led will bright more on positive peaks than in negatives, whet it tends to go dark. So, excepting a strong low pass filter, it will create hard distortion.
No. LDRs have quite long decay and relatively fast attack. And even in SE peaks are almost symmetric, however it depends on the sound material. With PP it is ideal.
Page 34, fugure 2.
http://denethor.wlu.ca/pc300/optoisolators/analogoptoisolatorintroduction.pdf
Even if it adds some negligible distortions of bass, they are much less nasty sounding that would sound clipping.
Here is the demo, on 0:55
https://www.facebook.com/Wavebourn/videos/1365809046810726/
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Audio is 99.99% subjective and personal taste, so if you are satisfied, then enjoy it very much, and other's opinion (Including mine) don't account; but from a simple theoretical point of view, the idea dislikes me, although I didn't test it, nor I will.
Sounds good to me! The less you and others like it, the better my amps sound on the background of "better" amps. ;-)
Sincerely,
Anatoliy Lisovskiy,
MS EE 1981, "Design and manufacturing of radio and electronics equipment"
Sincerely,
Anatoliy Lisovskiy,
MS EE 1981, "Design and manufacturing of radio and electronics equipment"
Strange thing, but I haven't lost a sweep tube from anything related to the screen. Sweep tubes seem to have very robust screens.
So, I would like to ask the original poster what tube/valve is in question, and what the operating points are.
Ian
So, I would like to ask the original poster what tube/valve is in question, and what the operating points are.
Ian
Yes, I fear you are right. Yet if we remain silent these silly ideas will completely take over.Osvaldo de Banfield said:
Action speaks louder than word.
I have about 20 units of guitar amp for proof, where are yours?!
To prove that series diodes are useless?
When they are always open, with low dynamic resistance in respect to the load, and 0.7V drop that is nothing compared to the voltage they supply, you can remove them and listen for yourself.
People with experience (and sales) often believe that experience (and sales) somehow automatically either replaces or enhances understanding. It can't do the former, and sadly it does not always do the latter.Koonw said:
A diode will either conduct or not conduct. In this position (screen feed) it will either do nothing or do harm, except for the small possibility of damping parasitic oscillation.
Someone somewhere sometime came up with this daft idea, probably based on some misunderstanding of how valves work, and others now propagate it.
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