@6A3sUMMER
With respect to you and others, you are carrying a lot of names of stuff (and names of the so called inventors of). As an Electronic Engineer I don't really hold truck with building circuits from names of functions like this, each circuit is different. For example I can call a circuit Grounded Base and I have seen many but very few get the bias needed for common base right.
Also very few of these composite circuits can be anything but compromises, once you tie two devices closely together it constrains how they are biased and whether the devices are working along the best load line for their characteristic curves.
All that said @6A3sUMMER I value and respect your detailed knowledge of circuitry and knowledge of written theory and historic development thereof. I do not have this knowledge and its interesting. For example I did not know that the Grounded Base was the first configuration ever used by the inventors of the Transistor.
We are on the same side here and on the same page here - wanting to know the truth of how circuits work for one thing. I'm going to put the circuit that @nilsW posted into LTspice and try to work it out and get back to you.
@nilsW Looking at your photo of your Analog Metric Preamp C7 and C10 both look as far as I can tell from the photo a bit swollen (the top) might be an idea to check or replace them. By the way the HT is 400 Volts so packs quite a painful punch for a Preamp.
With respect to you and others, you are carrying a lot of names of stuff (and names of the so called inventors of). As an Electronic Engineer I don't really hold truck with building circuits from names of functions like this, each circuit is different. For example I can call a circuit Grounded Base and I have seen many but very few get the bias needed for common base right.
Also very few of these composite circuits can be anything but compromises, once you tie two devices closely together it constrains how they are biased and whether the devices are working along the best load line for their characteristic curves.
All that said @6A3sUMMER I value and respect your detailed knowledge of circuitry and knowledge of written theory and historic development thereof. I do not have this knowledge and its interesting. For example I did not know that the Grounded Base was the first configuration ever used by the inventors of the Transistor.
We are on the same side here and on the same page here - wanting to know the truth of how circuits work for one thing. I'm going to put the circuit that @nilsW posted into LTspice and try to work it out and get back to you.
@nilsW Looking at your photo of your Analog Metric Preamp C7 and C10 both look as far as I can tell from the photo a bit swollen (the top) might be an idea to check or replace them. By the way the HT is 400 Volts so packs quite a painful punch for a Preamp.
richgwilliams,
I am glad for your posts!
You have questions, and so do many newbies, and so do old salts like me.
When I answer a particular person's post, I am Also hoping that others will benefit from my discussion.
When proper names are properly used, those who know the original usage and meaning of those proper names are not confused (+),
and others can now know the original and unchanged meanings.
The Senator said: Irregardless. In common English spellings "Ir" means Not.
But for the Senator, who wants to Emphasize his point . . . he says Irregardless, But he means: Regardless.
A commonly used tube name is Beam Power Tetrode. It has an Indirectly heated Cathode, a Control Grid, a Screen Grid, and a Plate . . .
Plus the Beam Formers. I count that as 5 elements (not counting the filament, since the Cathode is indirectly heated).
5 elements are responsible for the complete nature of the tube parameters and curves.
To use the word Tetrode here, is Neither grammatically correct, Nor mathematically correct.
But this is what happens with modernization of words (and This particular modernization was many decades ago).
A True Tetrode has a Cathode, Control Grid, Screen Grid, and a Plate . . . 4 elements, I believe the word Tetrode is a derived from the Greek: Tetra (4).
A Common Base Circuit to try . . .
I always wanted to build a Common Base NPN or PNP phono preamp input stage for a Moving Coil phono cartridge.
The emitter has to be capacitor coupled to the Moving Coil.
We do not want to pass DC current through those super fine coil wires . . . or burnout occurs.
A CCS (constant current Sink) of 0.25mA for the emitter, makes the emitter input impedance be about 104 Ohms, Ideal for many moving coils.
Have Fun!
I am glad for your posts!
You have questions, and so do many newbies, and so do old salts like me.
When I answer a particular person's post, I am Also hoping that others will benefit from my discussion.
When proper names are properly used, those who know the original usage and meaning of those proper names are not confused (+),
and others can now know the original and unchanged meanings.
The Senator said: Irregardless. In common English spellings "Ir" means Not.
But for the Senator, who wants to Emphasize his point . . . he says Irregardless, But he means: Regardless.
A commonly used tube name is Beam Power Tetrode. It has an Indirectly heated Cathode, a Control Grid, a Screen Grid, and a Plate . . .
Plus the Beam Formers. I count that as 5 elements (not counting the filament, since the Cathode is indirectly heated).
5 elements are responsible for the complete nature of the tube parameters and curves.
To use the word Tetrode here, is Neither grammatically correct, Nor mathematically correct.
But this is what happens with modernization of words (and This particular modernization was many decades ago).
A True Tetrode has a Cathode, Control Grid, Screen Grid, and a Plate . . . 4 elements, I believe the word Tetrode is a derived from the Greek: Tetra (4).
A Common Base Circuit to try . . .
I always wanted to build a Common Base NPN or PNP phono preamp input stage for a Moving Coil phono cartridge.
The emitter has to be capacitor coupled to the Moving Coil.
We do not want to pass DC current through those super fine coil wires . . . or burnout occurs.
A CCS (constant current Sink) of 0.25mA for the emitter, makes the emitter input impedance be about 104 Ohms, Ideal for many moving coils.
Have Fun!
"I always wanted to build a Common Base NPN or PNP phono preamp input stage for a Moving Coil phono cartridge.
The emitter has to be capacitor coupled to the Moving Coil."
First sentence : this is possible and not hard to do.
Second sentence : I can not recommend an input capacitor, because the charging current may be dangerous.
The emitter has to be capacitor coupled to the Moving Coil."
First sentence : this is possible and not hard to do.
Second sentence : I can not recommend an input capacitor, because the charging current may be dangerous.
Ditto.
So I have done the LTspice simulation and understand much better as follows:
Describing the Left channel, U1 and U2 are a "Long Tailed Pair" the input signal at the Grid of U1 is balanced with the feedback signal at the Grid of U2. The classic Opamp differential input. This works well if the current passing from U1 Anode to Cathode is reasonably equal to the current passing from U2 Anode to Cathode. The only way input signal gets from U1 to U2 and therefore U3 is by the current balancing in R7. Can also think of U1 and U2 as "Cathode Followers" U1 follows the input and U2 follows the feedback.
I don't see a "Grounded Base" configuration anywhere here.
Also being honest I'm not sure what U3 is doing but I think its another "Cathode Follower" and you can see it providing more output current.
The Analog Metric circuit seemed to be unbalanced when simulated, I had to reduce the value of R4 from 3K to 1K2 and I reduced the value of R6 from 20K to 15K. After doing this the "Long Tailed Pair" balanced with about 2mA passing through U1 and about 2mA passing through U2. So the current through R7 is about 4mA and the voltage across R7 is about 200 volts so it will dissipate nearly 1 Watt and get warm.
The voltage at the Plate of U1 should be roughly equal to the voltage at the Plate of U2 and should be somewhere not much lower than 90 Volts. The Left and Right channels share the same bias resistor, the 30K R1, this is a bit of a pain because balance in one channel affects balance in the other, it made the simulation more difficult (have to show both Left and Right channels).
The voltage gain from input to output is about x5 to x6. Total Harmonic Distortion for the values shown is better than -60dB but if current is drawn from the output (more than micro Amps) the THD will get worse.
As a general comment the voltage across any of the tubes U1 U2 U3 U4 U5 U6 is never more than 100 volts and the current through any of them is never much more than 2mA so they are not working at the most linear part of their characteristic curves, more voltage more current would be better. I was surprised when you consider that the total HT voltage is about 400 Volts from the positive rail to the negative rail!
@nilsW For your Analog Metric circuit you could consider reducing R7 and R8 to 1K2 and reducing R11 and R12 to 15K.
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An RCA phono input with the outside connection grounded, & an RCA phono output with the outside connection grounded, have one thing in common;
Signal Common Ground.
A triode with its cathode connected to a self bias resistor that has the other end of the resistor connected to ground. And there is no bypass capacitor.
If the signal is fed to the grid, and the output is taken from the plate, we call it a common cathode stage.
Ok. I can agree to call it that.
But, even though the cathode is the one triode element that is common to both the input and to the output . . .
It is not common to the input Signal Ground, and it is not common to the output Signal Ground.
The degeneration of the un-bypassed self bias resistor prevents it from being at Signal Ground.
Just a fine distinction.
Signal Common Ground.
A triode with its cathode connected to a self bias resistor that has the other end of the resistor connected to ground. And there is no bypass capacitor.
If the signal is fed to the grid, and the output is taken from the plate, we call it a common cathode stage.
Ok. I can agree to call it that.
But, even though the cathode is the one triode element that is common to both the input and to the output . . .
It is not common to the input Signal Ground, and it is not common to the output Signal Ground.
The degeneration of the un-bypassed self bias resistor prevents it from being at Signal Ground.
Just a fine distinction.
ejp,
You said:
"It is common to both signal input and signal output. Something has to be, and this is it."
Isn't hat like saying that the control grid is common to the signal input, due to the fact that the far end of the grid resistor, Rg, goes to ground.
After all, the far end of the cathode self bias resistor also goes to ground.
Both the grid, and the cathode are moving versus RCA Signal Ground. Right?
If you put a bypass capacitor across the self bias resistor, THEN the cathode IS at Signal Ground.
The operation with a bypass can, and without a bypass cap, is not the same.
Negative feedback to any of the 3 triode elements, affects the operating mode of the triode.
Call it what you want, it is not the Classic original circuit.
Definitions may, or may not, change.
You said:
"It is common to both signal input and signal output. Something has to be, and this is it."
Isn't hat like saying that the control grid is common to the signal input, due to the fact that the far end of the grid resistor, Rg, goes to ground.
After all, the far end of the cathode self bias resistor also goes to ground.
Both the grid, and the cathode are moving versus RCA Signal Ground. Right?
If you put a bypass capacitor across the self bias resistor, THEN the cathode IS at Signal Ground.
The operation with a bypass can, and without a bypass cap, is not the same.
Negative feedback to any of the 3 triode elements, affects the operating mode of the triode.
Call it what you want, it is not the Classic original circuit.
Definitions may, or may not, change.
Thank you all for comments. It has been very educational altough I must admit some of it above my paygrade!🙂
Thank you very much richgwilliams for the simulation and advice!
I will also check the capacitors
Thank you very much richgwilliams for the simulation and advice!
Do I have to change R4, R6, R7, R8,R11 and R12, or should I leave R4 and R6 unchanged?
I will also check the capacitors