# Equivalent circuits and more signal flow diagrams

Discussion in 'Amp Tech Center' started by peteb, Jun 4, 2018.

1. ### LudwigvonBirkTele-Holic

Age:
116
Aug 26, 2017
OP:

Can you provide math that supports your hypothesis?

Yep that's ^ a big ask, and is very hard to do. You can do it. Please do it!

...
Further:

If not immediately obvious, the last thing anybody should do is piss off the 50+ year-old physicists, they are capable of building and delivering very dangerous weapons. We MUST keep them focused on tube-amp math and similar harmless things. Help me on that and save us all!!!!

Wally and Bendyha like this.

Mar 26, 2014
Northern Germany
Equivalent AC circuits also remove things like tubes, and replace them with a designated symbol to express the separate relevant functions, in this case one being as an AC source. One should avoid establishing a bias towards a partial selectivity of a components functions, for example; should not the plate resistance of the tube also be included ?

A partially equivalent circuit is usually fairly useless. Therefor, either the circuit should be symbolized and designated in the contemporary manner as one finds it in most schematics, so that every interrelating function can be assessed, or transformed into a Thévenin equivalent circuit, where every interrelating component has been taken into account, and a true equivalent can be represented in a manner that is usefull to analysing the circuit and any interrelationship between components that can then be assessed.

Last edited: Jun 7, 2018
3. ### robrobPoster ExtraordinaireAd Free Member

Dec 29, 2012
United States
The AC guitar audio signal moving through an amp is not a standing wave.

A signal may look like a standing wave on an oscilloscope due to its trigger function. Turn off the trigger and watch your "standing wave".

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4. ### D'tarTele-Afflicted

Jan 11, 2013
WNY
These are only Out Of Phase if they occur at the same time?

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5. ### petebFriend of Leo's

Apr 25, 2003

for sure. I also have more wave theory stuff

thanks

I cant do it now however

6. ### petebFriend of Leo's

Apr 25, 2003

Thanks Bendyha, I will go over what you wrote and reply.

7. ### petebFriend of Leo's

Apr 25, 2003

thanks Rob. I have some more wave stuff to go over. I would really like to hear your input. Could you show us the moving wave?

I have no problem with the moving wave.

actually, I would like to see the moving wave but I don't need to.

What I have found is that a standing wave is two moving waves, in opposite directions, like I think is happening on the load resistors.

I have been interested in wave theory for a long time but had no place to apply it. I found the wave on the load resistors is a great place to study wave behavior.

8. ### petebFriend of Leo's

Apr 25, 2003

Thanks D"tar,

doesn't one phase happen and then the other?

in - out - in - out - in

I think it works

9. ### D'tarTele-Afflicted

Jan 11, 2013
WNY
• One cycle of a wave is one complete evolution of its shape until the point that it is ready to repeat itself.
• The period of a wave is the amount of time it takes to complete one cycle.

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10. ### petebFriend of Leo's

Apr 25, 2003
D'tar,

Look at your example. specifically first 180 degrees of A, the hump.

It is out of phase with both the first 180 degrees of B and the second 180 degrees of A.

That's why the name phase inversion is accurate and also misleading.

most people look at what a phase inverter does and if its function is to be described they would say that it inverts the signal which it does, which is equivalent to a 180 degree phase shift.

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11. ### petebFriend of Leo's

Apr 25, 2003

isn't this the needed math:

the signal on the plate of the cathodyne phase inverter varies sinusoidaly between say plus and minus 20 volts.

the signal on the cathode does the same but is out of phase by 180 degrees from the plate.

the signal on the node between the plate and cathode resistors remains at zero VAC because it is an AC or signal ground.

this is all agreed upon and the next step is to connect the dots and graphically show what the signal voltage is at every point between the plate and the cathode along the connected plate and cathode resistors.

12. ### petebFriend of Leo's

Apr 25, 2003

Bendyha, I don't know, should it?

I understand that the tube as a power supply has its own internal resistance.

I'm not sure what to do with it.

the signal voltage on the plate develops on the external plate load resistor.

same with the cathode and the external cathode resistor.

if we want to look at the cathodyne phase inverter, specifically how the signal voltages on the plate and the cathode develop or where they come from, shouldn't the focus be on the external load resistances which causes these signal voltages to appear?

all tubes have this internal resistance but what makes a cathodyne PI a cathodyne PI is how the tube is wired into the circuit. It is the equal plate and cathode load resistors, both half size of a normal plate load resistor, that make the cathodyne PI do what it does.

13. ### petebFriend of Leo's

Apr 25, 2003

http://www.valvewizard.co.uk/Common_Gain_Stage.pdf

look at figure 1.7d on page 28. It is Blencoe's Thevenin equivalent circuit for a triode.

It is nearly equivalent to my equivalent circuit diagram for the cath PI. I drew my equivalent circuit with the help of the TDPRI before I had ever seen one done before or seen a thevenin diagram.

The only difference between Blencoe's and mine is that he has the internal plate load resistance in his and I don't in mine. and like I said, I don't see how leaving the internal plate load resistance off of mine makes it wrong because the internal plate load resistance is not needed to explain how the cath PI works.

14. ### D'tarTele-Afflicted

Jan 11, 2013
WNY
I can't only look @ the 1st 180° because one cycle is 360°. The phase inverter does just that, it inverts the wave identicle to the input. It is a mirror image affect just like my example.

15. ### petebFriend of Leo's

Apr 25, 2003
my point is that inversion is identical to a 180 degree phase shift, i.e. 1-180 becoming 180-360.

A is out of phase with B.

if you prefer 1-360 degrees, try this.

shift the first 360 degrees of A by 180 degrees to the right.

what do you get?

you get one full cycle that is inverted or 180 degrees out of phase with the original full cycle.

16. ### petebFriend of Leo's

Apr 25, 2003
More wave theory:

here is a particle diagram that could model the signal wave traveling thru the amp.

not sure if there is more to say..

Apr 25, 2003

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Apr 25, 2003