dubadub,
6B4G looks OK:
Single ended amplifiers often have slightly different rise time versus fall time like yours, and some slight early overshoot, just like yours.
Based on the rise and fall times, the bandwidth is about 35kHz; better than most ears, and better than most tweeters.
Bats anybody?
The amplifier is not going to win a magazine review, but it still is listenable.
Is there No negative feedback, or does it Have negative feedback?
I can not look at your schematic while I am typing this.
Sounds good, so . . . Enjoy the music.
The single ended EL84:
Is it in Pentode mode (screens to a B+ voltage); Ultra Linear mode (screens to the Ultra Linear taps), or in Triode mode?
I am guessing Pentode mode.
Negative feedback present, or not?
If it is not in Triode mode, then connect the screens through 100 Ohm resistors to their respective plates.
Triode mode = less power, but more finesse. Check the 10k square wave again.
If you have a PCB, you can cut the screen traces if needed to connect a 100 Ohm resistor from the screen to the plate (Triode mode).
Then you can take the resistor out, scrape the PCB trace on each side of the cut, carefully tin the traces there, and carefully solder a tinned wire across the cut (back to the original circuit you had).
Anyway, even if the screen shot looks a little ugly, the sound probably is OK.
That is because most music does not have any harmonics at 30kHz, which is the lowest frequency harmonic of the 10kHz square wave that you are seeing on the screen shot.
As built, sounds OK or not?
Triode wire if not. A little trouble might make a much prettier screen shot.
Next time, lets see a 1kHz sine wave signal to each amplifier, adjust the signal level to where it just clips, and then reduce the signal level to where it looks like a sine wave again.
Measure the rms volts, Vrms.
((Vrms)squared) / 8 Ohms = Watts rms into 8 Ohms.
Have Fun!
6B4G looks OK:
Single ended amplifiers often have slightly different rise time versus fall time like yours, and some slight early overshoot, just like yours.
Based on the rise and fall times, the bandwidth is about 35kHz; better than most ears, and better than most tweeters.
Bats anybody?
The amplifier is not going to win a magazine review, but it still is listenable.
Is there No negative feedback, or does it Have negative feedback?
I can not look at your schematic while I am typing this.
Sounds good, so . . . Enjoy the music.
The single ended EL84:
Is it in Pentode mode (screens to a B+ voltage); Ultra Linear mode (screens to the Ultra Linear taps), or in Triode mode?
I am guessing Pentode mode.
Negative feedback present, or not?
If it is not in Triode mode, then connect the screens through 100 Ohm resistors to their respective plates.
Triode mode = less power, but more finesse. Check the 10k square wave again.
If you have a PCB, you can cut the screen traces if needed to connect a 100 Ohm resistor from the screen to the plate (Triode mode).
Then you can take the resistor out, scrape the PCB trace on each side of the cut, carefully tin the traces there, and carefully solder a tinned wire across the cut (back to the original circuit you had).
Anyway, even if the screen shot looks a little ugly, the sound probably is OK.
That is because most music does not have any harmonics at 30kHz, which is the lowest frequency harmonic of the 10kHz square wave that you are seeing on the screen shot.
As built, sounds OK or not?
Triode wire if not. A little trouble might make a much prettier screen shot.
Next time, lets see a 1kHz sine wave signal to each amplifier, adjust the signal level to where it just clips, and then reduce the signal level to where it looks like a sine wave again.
Measure the rms volts, Vrms.
((Vrms)squared) / 8 Ohms = Watts rms into 8 Ohms.
Have Fun!
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the SE amp is the one from Post #1. no feedback.
I'll prob put these fancy OPTs in a different amp one day, for now I'm stuck with the single driver tube socket, so it's 6SL7 or bust. Guess I could look at a 6SN7 with choke-loaded plates...🤔
I'll prob put these fancy OPTs in a different amp one day, for now I'm stuck with the single driver tube socket, so it's 6SL7 or bust. Guess I could look at a 6SN7 with choke-loaded plates...🤔
Perhaps we can set a little more current for the 6SL7 to get its plate impedance, rp, a little lower, and get a little more symmetrical rp versus signal swing.
That only requires changes of the resistance of the cathode self bias resistor, and the plate load resistor.
The 6SN7 can work well, as long as you will have enough amplifier gain, versus the signal source voltages you have, and your speaker power requirements for how loud you want to listen.
Most of my listening is done near-field, about 2 feet to 4 feet from my speakers.
For those locations, I do not need lots of gain, and I do not need lots of power.
That only requires changes of the resistance of the cathode self bias resistor, and the plate load resistor.
The 6SN7 can work well, as long as you will have enough amplifier gain, versus the signal source voltages you have, and your speaker power requirements for how loud you want to listen.
Most of my listening is done near-field, about 2 feet to 4 feet from my speakers.
For those locations, I do not need lots of gain, and I do not need lots of power.
interesting, RCA Tube Manual shows a 6SL7 with 300v supply, 220k plate resistor, 470k grid leak, 3K2 cathode resistor as resulting in a voltage gain of 46, towards the high end of potential for the 6SL7. Maybe I'm reading it wrong.
Sometimes gain is paramount
Sometimes linearity is paramount
Sometimes maximum voltage swing is paramount.
They do not always happen at the same operating point.
Often for some tube types, RCA had a table of different quiescent conditions, that included the 3 factors above.
A graph of plate impedance, rp, versus plate current would be interesting too.
The 6SL7 is a good performer.
The 6SN7 also is a good performer.
They have different tradeoffs related to the circuit values, voltages, current, and load impedances.
The factor of slew rate (rise time and fall time) of the output tube grid signal voltage is its Miller Effect Capacitance, versus the driving impedance.
The driving impedance is the parallel of:
6SL7 plate rp, 44k Ohms at 2.3mA (but Higher resistance at lower current)
270k Ohms RL
470k Ohms Rg (of the output tube)
As the 6SL7 plate current varies, rp varies, and that may be the difference of the rise time and fall time. rp is dominant versus 270k and 470k.
Sometimes linearity is paramount
Sometimes maximum voltage swing is paramount.
They do not always happen at the same operating point.
Often for some tube types, RCA had a table of different quiescent conditions, that included the 3 factors above.
A graph of plate impedance, rp, versus plate current would be interesting too.
The 6SL7 is a good performer.
The 6SN7 also is a good performer.
They have different tradeoffs related to the circuit values, voltages, current, and load impedances.
The factor of slew rate (rise time and fall time) of the output tube grid signal voltage is its Miller Effect Capacitance, versus the driving impedance.
The driving impedance is the parallel of:
6SL7 plate rp, 44k Ohms at 2.3mA (but Higher resistance at lower current)
270k Ohms RL
470k Ohms Rg (of the output tube)
As the 6SL7 plate current varies, rp varies, and that may be the difference of the rise time and fall time. rp is dominant versus 270k and 470k.
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Hashimoto HC-203U is an old transformer, but enough good for this amp.
https://jelabs.blogspot.com/2013/12/hashimoto-hc-203u-se-output-transformer.html
"The HC-203U is a bold performer and gives a front row presentation. Given its rather small stature, it has bass slam and definition that I associate with transformers twice its size. Vocals are presented in a lifelike manner and there is enough extension in the highs to give a sense of spaciousness and airiness."
Fr., 10k SQ
The induction not so high, but each Hashimoto such "slim".
I would measure this amplifier with better measuring set.
https://jelabs.blogspot.com/2013/12/hashimoto-hc-203u-se-output-transformer.html
"The HC-203U is a bold performer and gives a front row presentation. Given its rather small stature, it has bass slam and definition that I associate with transformers twice its size. Vocals are presented in a lifelike manner and there is enough extension in the highs to give a sense of spaciousness and airiness."
Fr., 10k SQ
The induction not so high, but each Hashimoto such "slim".
I would measure this amplifier with better measuring set.
I'm still not clear on the differences between voltage gain, wattage, and output power. But this amp and speakers certainly has enough of what it takes to make my wife mad. So I could probably sacrifice a bit of voltage gain. 100k plate resistors would prevent rp from playing such a large role? Could try 100k plate resistors and 2k1 Kr without changing anything else.
Voltage gain is what it says.
You put an input voltage in the amp and the output voltage is measured.
Gain is output voltage divided by input voltage. Don't overthink it.
Watt is a unit, just like foot or acre. It is the unit to measure power, and is voltage times amps.
Just like your light bulb has a power rating expressed in Watts.
A 110V bulb rated 220W will draw 2 Amps from the mains, as power (220) is V (110) x I (2) in Watts.
'Wattage' is a term often heard from non-technical people but doesn't really exist and has no meaning.
The term is power, and power is expressed in Watts and is voltage x current.
A 5V power supply delivering 1.5 Amp into a resistor is supplying 5 x 1.5 = 7.5 Watts to that resistor.
Output power, again, just what it says. If your amp delivers an output voltage to a load, that causes a current to flow into the load.
This represents a power of Vout x Load current, again expressed in Watts.
Again, don't overthink it - just use the definition. Not rocket science.
Jan
You put an input voltage in the amp and the output voltage is measured.
Gain is output voltage divided by input voltage. Don't overthink it.
Watt is a unit, just like foot or acre. It is the unit to measure power, and is voltage times amps.
Just like your light bulb has a power rating expressed in Watts.
A 110V bulb rated 220W will draw 2 Amps from the mains, as power (220) is V (110) x I (2) in Watts.
'Wattage' is a term often heard from non-technical people but doesn't really exist and has no meaning.
The term is power, and power is expressed in Watts and is voltage x current.
A 5V power supply delivering 1.5 Amp into a resistor is supplying 5 x 1.5 = 7.5 Watts to that resistor.
Output power, again, just what it says. If your amp delivers an output voltage to a load, that causes a current to flow into the load.
This represents a power of Vout x Load current, again expressed in Watts.
Again, don't overthink it - just use the definition. Not rocket science.
Jan
That output transformer has a 2.5k Ohm primary tap, and it also has a 3.5k Ohm primary tap.
If you connect the 6B4G plate to the 3.5k primary tap, then the complete transformer primary windings will be driven.
With the 2.5k tap, the extra windings from the 2.5k tap to the 3.5k tap, are just "hanging" free; might resonate.
That is a very easy modification to try . . . slightly lower gain, slightly lower power out, slightly lower distortion, and higher damping factor.
It will be interesting to see the changes in rise time, fall time, etc.
But before you even do that simple modification, use your scope probes to look at the signal on the grid of the 6B4G.
Rise time, fall time, etc.
Have fun!
If you connect the 6B4G plate to the 3.5k primary tap, then the complete transformer primary windings will be driven.
With the 2.5k tap, the extra windings from the 2.5k tap to the 3.5k tap, are just "hanging" free; might resonate.
That is a very easy modification to try . . . slightly lower gain, slightly lower power out, slightly lower distortion, and higher damping factor.
It will be interesting to see the changes in rise time, fall time, etc.
But before you even do that simple modification, use your scope probes to look at the signal on the grid of the 6B4G.
Rise time, fall time, etc.
Have fun!