Hello. I have a push pull of el34, running at 450Vdc on the plates. I want to have 50W.
This is not an ultralinear OT I am looking for.
How can I choose an OT for the lowest IMD ?
Thank you.
This is not an ultralinear OT I am looking for.
How can I choose an OT for the lowest IMD ?
Thank you.
I am not certain that if you require 50 Watts, 450V plate (to cathode?), and EL34 in Pentode Mode, that it will necessarily be the lowest IMD (at least four or five interlocking parameters).
Lowest IMD of 1kHz and 1.35kHz, lowest IMD of 30Hz and 1 kHz, or lowest IMD of 7kHz and 9kHz?
2nd order IMD?
3rd order IMD?
Global Negative feedback from the secondary?
Or . . .
Schade Negative feedback from the primary?
The primary determinant is probably the plate to plate impedance.
Next, the laminations size and material.
The tradeoff with larger laminations might be the high frequency bandwidth limits, etc.
Your question reminds me of STP from Physics.
Standard Temperature and Pressure of air in a fixed size enclosure.
You can not change one of the three: S, T, or P, without changing one or both of the other parameters.
I'm sorry that I can not really be of more help in this matter.
I am sure you will get various answers from others.
Happy amplifier designing!
Happy building and listening!
Lowest IMD of 1kHz and 1.35kHz, lowest IMD of 30Hz and 1 kHz, or lowest IMD of 7kHz and 9kHz?
2nd order IMD?
3rd order IMD?
Global Negative feedback from the secondary?
Or . . .
Schade Negative feedback from the primary?
The primary determinant is probably the plate to plate impedance.
Next, the laminations size and material.
The tradeoff with larger laminations might be the high frequency bandwidth limits, etc.
Your question reminds me of STP from Physics.
Standard Temperature and Pressure of air in a fixed size enclosure.
You can not change one of the three: S, T, or P, without changing one or both of the other parameters.
I'm sorry that I can not really be of more help in this matter.
I am sure you will get various answers from others.
Happy amplifier designing!
Happy building and listening!
Last edited:
Frederico Acardi,
Use a 1,500 Ohm plate to plate impedance, and you will get high harmonic distortion, high intermodulation distortion; as well as low power output.
Not good.
Use a 10,000 Ohm plate to plate impedance, and you will get low harmonic distortion, low intermodulation distortion; as well as low power output.
Not good in the power department.
Better
Somewhere in between those above listed plate to plate impedances, you will get medium harmonic distortion and medium intermodulation distortion,
But you will get more power output.
I am guessing that somewhere between 3,500 Ohms and 6,600 Ohms plate to plate, you will find a good compromise of distortion and power.
The EL34 Dyna Stereo 70 used 4,400 Ohms plate to plate and got fairly good distortion results, with power out about 35 to 28 Watts (depending on mid; versus low and high frequency extremes).
The EL34 maximum plate dissipation is 25 Watts. With 450V plate to cathode, the maximum quiescent plate current is 55.5mA.
You still did not say anything about your circuit topology (input stage, phase inverter, driver. Local negative feedback, multiple negative feedback loops, other negative feedback such as Schade negative feedback, and global negative feedback from the output transformer secondary.
If you really want 50 Watts output power, you might consider using KT88s, and a very low loss output transformer.
To get 50 Watts output, if the output transformer has 1 dB insertion loss, then you will need 63 watts from the output tubes going to the output transformer primary. Fact of life.
Just my opinions.
Use a 1,500 Ohm plate to plate impedance, and you will get high harmonic distortion, high intermodulation distortion; as well as low power output.
Not good.
Use a 10,000 Ohm plate to plate impedance, and you will get low harmonic distortion, low intermodulation distortion; as well as low power output.
Not good in the power department.
Better
Somewhere in between those above listed plate to plate impedances, you will get medium harmonic distortion and medium intermodulation distortion,
But you will get more power output.
I am guessing that somewhere between 3,500 Ohms and 6,600 Ohms plate to plate, you will find a good compromise of distortion and power.
The EL34 Dyna Stereo 70 used 4,400 Ohms plate to plate and got fairly good distortion results, with power out about 35 to 28 Watts (depending on mid; versus low and high frequency extremes).
The EL34 maximum plate dissipation is 25 Watts. With 450V plate to cathode, the maximum quiescent plate current is 55.5mA.
You still did not say anything about your circuit topology (input stage, phase inverter, driver. Local negative feedback, multiple negative feedback loops, other negative feedback such as Schade negative feedback, and global negative feedback from the output transformer secondary.
If you really want 50 Watts output power, you might consider using KT88s, and a very low loss output transformer.
To get 50 Watts output, if the output transformer has 1 dB insertion loss, then you will need 63 watts from the output tubes going to the output transformer primary. Fact of life.
Just my opinions.
Last edited:
My point of view
To get 50w from a pair of EL34 with a reasonable THD also at max is almost impossible.
The OT is the mains problem to solve and to get one good you have to spent money.
In my opinion is always better the use of the high Z ( so an high ratio prim/sec) and, possible a single secondary. I use 5 ohm fix, with 5k a-a ; around 30-32 as ratio
The reason is due the variation of the impedance of the loudspeaker mainly around mid-low frequency where the energy that the amp must deliver to load is great.
Having an high ratio and good impedance if the dinamic line load ( that is not linear but an ellipse) stay, in the worst case, in a safety field.
Of course also the specs for high frequency must be fine.
One other thing is the selection (dynamic) of the output tubes to reach the lowest THD.
Last, the start point is the input/splitter circuit must have a good linearity from low to high level of signal.
Walter
To get 50w from a pair of EL34 with a reasonable THD also at max is almost impossible.
The OT is the mains problem to solve and to get one good you have to spent money.
In my opinion is always better the use of the high Z ( so an high ratio prim/sec) and, possible a single secondary. I use 5 ohm fix, with 5k a-a ; around 30-32 as ratio
The reason is due the variation of the impedance of the loudspeaker mainly around mid-low frequency where the energy that the amp must deliver to load is great.
Having an high ratio and good impedance if the dinamic line load ( that is not linear but an ellipse) stay, in the worst case, in a safety field.
Of course also the specs for high frequency must be fine.
One other thing is the selection (dynamic) of the output tubes to reach the lowest THD.
Last, the start point is the input/splitter circuit must have a good linearity from low to high level of signal.
Walter