# How can you tell if your amp is operating class A or class AB?

Discussion in 'Amp Tech Center' started by peteb, Jul 24, 2018.

1. ### BendyhaFriend of Leo'sSilver Supporter

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Make my day pete...
Well, sure laughed a lot so far.......

"You showed the AC changing. And said that changed the DC. I would really like to see the DC change. Why didn’t you show the DC?"

.........classic.......keep it coming.

2. ### elpicoTele-Afflicted

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Yes, that's what I've been telling you since my first post on the subject a week ago.

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3. ### elpicoTele-Afflicted

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You can name it whatever you want but it changes nothing - it's showing the actual, real voltage on the plate at any given time ...and that is clearly changing. To make this measurement you have to set your oscilloscope to "DC" coupling, not "AC".

4. ### petebFriend of Leo's

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Elpico,

I believe you said energy that contributes to dissipation and redplate is DC only, and then you reversed position and said the AC in the tube has to dissipate too.

I don’t mind you changing positions, while I have not, but please don’t call me confused when you have not been very assured your self.

5. ### TeleTucsonTele-Afflicted

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Yeah, I said I cringed to bring it up ... and that it wasn't central to Pete's misunderstanding. But I have trouble watching mis-statement propagate and become entrenched, which is why I made the comment.

Wrong, wrong, wrong ... This statement indicates that you don't understand Fourier analysis. Fourier analysis can represent any signal, even a single blip in an arbitrary interval of time. You give me an arbitrary, non-repeating signal, and I can represent if faithfully in the frequency domain without approximation. And you can talk about power in the time domain or frequency domain, and power within a frequency band centered on an arbitrary frequency, etc., etc. But teaching signal analysis on TDPRI is not one of my ambitions.

Last edited: Jul 25, 2018
6. ### petebFriend of Leo's

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Agreed, it’s puzzling why the AC current doesn’t add heat. I think we are on to something to explain it.

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7. ### petebFriend of Leo's

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We all know it’s true, why deny it?

First you say the AC has to add heat, then you say there is no AC.

??

And also, you say there is no AC and then show us a plot of AC and call it DC.

Very confusing.

You are saying if there was AC it would add heat.

Actually, there is AC and I think we are onto why it doesn’t add heat.

Last edited: Jul 25, 2018

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9. ### petebFriend of Leo's

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I think this holds the very key we are looking for.

Thanks

10. ### petebFriend of Leo's

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Thanks for clarifying. It is AC and DC, everything.

At one point you said it was not AC, that was confusing!

11. ### petebFriend of Leo's

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Here is the scoop.

Class A operation: constant DC power supply, unlike class AB that increases with signal.

Everyone is favoring that with signal, heat dissipation gets lessened as more energy is transferred to making audio out power. (Which is another form of dissipation but we won’t get into that)

Does class A actually dissipate less heat energy under signal conditions. Everyone including Randall Smith of Mesa amps likes this.

It is shaping up to look like this:

Idle:

12 W DC in———————————> 12 W heat dissipation out

Full signal:

12 W DC in———————————>6 W heat out + 6 W audio out

12. ### petebFriend of Leo's

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The question is why doesn’t the AC add heat?

This is the best explanation I am aware of.

Even though there is the AC component flowing thru the tube, it is not actual alternating current like Elpico says, the electrons do not “alternate” directions as they cannot flow backwards.

Current is electrons per time. If this AC component were large enough to cause electrons to reverse directions in travel, then there would be more electrons passing any given point over any given time, but since they don’t reverse, the over all net current flow is unchanged by the signal, in class A only.

Last edited: Jul 25, 2018
13. ### petebFriend of Leo's

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Here is what I don’t like about this. If the heat on the plate is caused by the kinetic energy of the electrons hitting the plate, I don’t see how this energy is going to lessen from 12 W to 6 W when the same amount of electrons are running into the plate at the same rate and speed.

14. ### TeleTucsonTele-Afflicted

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They're not - on the average, they're not running into the plate with the same speed.

15. ### petebFriend of Leo's

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Thanks Tele, please let me know what you think of post 92.

Are we on the same page?

16. ### BendyhaFriend of Leo'sSilver Supporter

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Peteb............................a misquote like that is so bad, and you have been asked not to do that several times, from me and from others.....but now you have at last proved something to me.............You are a truely horrible person to have here on the forum.

The self centered arrogance of twisting someone elses words to say the opposite of what was intended and then agreeing with your self in this manner....sick, sick...sick.

I will now report your post to the powers that be here, and hope they can do something about that blatent missrepresentation of such an honourable and helpfull member as elpico.

For me you are now a clearly a complete irrespossible fool, self centered, and thick as two short planks.

Expect no reaction from me other than derision and dissrespect.

17. ### Old Tele manFriend of Leo's

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What's that old fable? "You can lead a (thirsty) horse to water but you can't make him drink?"

18. ### robrobPoster ExtraordinaireAd Free Member

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Yea, for the good of all the tube amp enthusiasts that will find these threads in the future they really should be deleted.

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19. ### David BarnettDoctor of Teleocity

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It's like beating your head against a wall...

20. ### robrobPoster ExtraordinaireAd Free Member

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This is elpico's animated graph that shows exactly what you're asking about pete. This is how Class A works. If you don't understand what it's doing then do some research to figure it out:

Last edited: Jul 25, 2018
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