How to calculate the bias current on class A 6V6 PP amplifier ?
Supply voltage 330V
Output transfromer PP 5K
Speaker 8R
Supply voltage 330V
Output transfromer PP 5K
Speaker 8R
You can even use this useful tool selecting the tube you prefer:
Loadline calculator for power stages with reactive load - Vacuum Tube Amplifiers - DIY
Loadline calculator for power stages with reactive load - Vacuum Tube Amplifiers - DIY
You can follow the method in the site, but I think you'll need a composite curve load line for PP to be more accurate and additional params:
Screen supply:330V
DCR: 300 ohms
Cathode Resistor: Shared or independent.
Using the above method, bias required: -25V
If you want simulation file I can post here.
Screen supply:330V
DCR: 300 ohms
Cathode Resistor: Shared or independent.
Using the above method, bias required: -25V
If you want simulation file I can post here.
Attachments
If I ever design and build a 6V6 push pull amplifier, it will have the following:
1. Individual self bias resistors and bypass caps, one RC per each tube.
2. Matched 6V6 tubes. (My vendor does excellent tube matching).
Design, build, and it works first time, no adjustment needed ever.
I have not done that with 6V6 yet, but I have done that for push pull amplifiers using:
2A3, 300B, EL34, KT77, KT66, 6L6GC, 7591S, and 6BX7.
The individual self bias network method works real good for me.
And . . . just read the voltage across the self bias resistors, and see how well they match, when the tube is new, and when they have been operated for years.
Just my experience, and just my opinion.
1. Individual self bias resistors and bypass caps, one RC per each tube.
2. Matched 6V6 tubes. (My vendor does excellent tube matching).
Design, build, and it works first time, no adjustment needed ever.
I have not done that with 6V6 yet, but I have done that for push pull amplifiers using:
2A3, 300B, EL34, KT77, KT66, 6L6GC, 7591S, and 6BX7.
The individual self bias network method works real good for me.
And . . . just read the voltage across the self bias resistors, and see how well they match, when the tube is new, and when they have been operated for years.
Just my experience, and just my opinion.
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It is easy: take a SE operating point, double the load, and keep the per-tube idle at the same voltage.
cheers,
Douglas
cheers,
Douglas
Bandersnatch,
Not all push pull amplifiers use that simple of a method to determine the operating conditions.
Just for an example, take a look at the old RCA data sheet that lists operating points for the 2A3.
Single ended 2A3 with -45V bias, and 2500 Ohm Primary gets 3.5 Watts @ 5% 2nd Harmonic Distortion.
Push pull 2A3 with -62V bias, and 3000 Ohm plate to plate primary gets 15 watts @ 2.5% Total Harmonic Distortion.
I suspect that likewise, a good 6V6 SE amp, and a good 6V6 Push Pull amp will have different operating conditions.
Not all push pull amplifiers use that simple of a method to determine the operating conditions.
Just for an example, take a look at the old RCA data sheet that lists operating points for the 2A3.
Single ended 2A3 with -45V bias, and 2500 Ohm Primary gets 3.5 Watts @ 5% 2nd Harmonic Distortion.
Push pull 2A3 with -62V bias, and 3000 Ohm plate to plate primary gets 15 watts @ 2.5% Total Harmonic Distortion.
I suspect that likewise, a good 6V6 SE amp, and a good 6V6 Push Pull amp will have different operating conditions.
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Hi 6A3sUMMER, the title of the thread refers to a class A PP.
Your example of a PP with 2A3 is in class AB.
I'd follow Bandersnatch suggestion for a class A PP.
Your example of a PP with 2A3 is in class AB.
I'd follow Bandersnatch suggestion for a class A PP.
Zintolo,
You are absolutely correct.
Have you ever overdriven a Class A push pull amplifier?
I have.
Even though it was designed as a Class A push pull amplifier, the push and pull tubes were alternately cut off during the peaks of the signal.
In like manner, a grossly overdriven Class A single ended amplifier becomes a Class C amplifier.
Based on the 1956 ARRL Radio Amateurs Handbook definitions.
You are absolutely correct.
Have you ever overdriven a Class A push pull amplifier?
I have.
Even though it was designed as a Class A push pull amplifier, the push and pull tubes were alternately cut off during the peaks of the signal.
In like manner, a grossly overdriven Class A single ended amplifier becomes a Class C amplifier.
Based on the 1956 ARRL Radio Amateurs Handbook definitions.
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Thanks for the personal experience, I've understood the issue with overdriven class A PP, but then what is the solution? Design PP in class AB only?
An interesting question, and one that dates back to the first variations of the DTN Williamson amplifier of the late 1940s. The original had a common, unbypassed, cathode bias resistor (with trimpots for bias and balance).
As the Power Wars (sometime before the Clone Wars) heated up, folks started bypassing the common cathode resistor. Then they cranked up the B+ and lowered the loading impedances, meaning lower idling currents. It became acceptable to operate through the cutoff region, but only on a small part of the operating cycle. A slippery slope.
Next thing we knew, there were silicon based life forms, that couldn't survive at high temperatures, so we accommodated them by operating near cutoff at idle. Monotonicity was dead, but we didn't care anymore - and now we're their servants, staring into glowing screens awaiting their commands. Typing, ever typing.
Soylent Green is people!
Chris
As the Power Wars (sometime before the Clone Wars) heated up, folks started bypassing the common cathode resistor. Then they cranked up the B+ and lowered the loading impedances, meaning lower idling currents. It became acceptable to operate through the cutoff region, but only on a small part of the operating cycle. A slippery slope.
Next thing we knew, there were silicon based life forms, that couldn't survive at high temperatures, so we accommodated them by operating near cutoff at idle. Monotonicity was dead, but we didn't care anymore - and now we're their servants, staring into glowing screens awaiting their commands. Typing, ever typing.
Soylent Green is people!
Chris
Well there 6A3, it just depends on the design methods. If you want to squeeze the most power out of a Class A design, you come closer and closer to cutting off one side. IME, keeping well away from cut-off conditions only costs a wee bit of power. I don't care to rate a cap coupled amp at power levels reached when it is well into grid current. That is just silly... 🙂
Ultimately, I prefer to run the system at power levels usually handled by liddle SE amps. Tri-amp active cross over, and efficient speakers. Even on the peaks, nothing bothersome is happening. All done with medium-sized class A amps. If those amps are running somewhere out of their comfort zone, I'll eat my hat...even if I load up something to play at elevated levels.
cheers,
Douglas
Ultimately, I prefer to run the system at power levels usually handled by liddle SE amps. Tri-amp active cross over, and efficient speakers. Even on the peaks, nothing bothersome is happening. All done with medium-sized class A amps. If those amps are running somewhere out of their comfort zone, I'll eat my hat...even if I load up something to play at elevated levels.
cheers,
Douglas
Bandersnatch,
Hi Fi Amplifiers:
What is the problem?
If you increase the drive signal to a Class A1 amplifier, so that it goes into Class AB1, I do not think anybody will hear a gross distortion, as long as it is not driven into clipping.
Just because a Class A1 amplifier is driven hard enough to go into Class AB1, that may not mean it is drawing grid current.
But, if you drive any Class of amplifier into hard clipping, that just might be a problem for many Hi Fi listeners . . . bothersome.
Class A2, Class AB2 indicates Grid current can be drawn, and usually means the designer intended to draw grid current (even at linear power levels).
But that does not mean they have to be clipping, just to draw grid current, in fact the designers want to be in A2 or AB2 without going into clipping.
The clipping level is according to the design.
Amplifiers vary as to how well, or how poorly, they perform when driven too hard.
Likewise, Loudspeakers vary as to how well, or how poorly, they perform when driven too hard.
Whether amplifiers run full range, or bi-amp, or tri-amp speakers, they are not Hi Fi if they clip.
Even if they draw draw grid current, they may, or they may not be distorted (even if they are not clipping).
Guitar Amplifiers and Speakers:
All Hi Fi rules can be broken, and the breaking of the Hi Fi rules may be intentional.
Just my opinions.
Hi Fi Amplifiers:
What is the problem?
If you increase the drive signal to a Class A1 amplifier, so that it goes into Class AB1, I do not think anybody will hear a gross distortion, as long as it is not driven into clipping.
Just because a Class A1 amplifier is driven hard enough to go into Class AB1, that may not mean it is drawing grid current.
But, if you drive any Class of amplifier into hard clipping, that just might be a problem for many Hi Fi listeners . . . bothersome.
Class A2, Class AB2 indicates Grid current can be drawn, and usually means the designer intended to draw grid current (even at linear power levels).
But that does not mean they have to be clipping, just to draw grid current, in fact the designers want to be in A2 or AB2 without going into clipping.
The clipping level is according to the design.
Amplifiers vary as to how well, or how poorly, they perform when driven too hard.
Likewise, Loudspeakers vary as to how well, or how poorly, they perform when driven too hard.
Whether amplifiers run full range, or bi-amp, or tri-amp speakers, they are not Hi Fi if they clip.
Even if they draw draw grid current, they may, or they may not be distorted (even if they are not clipping).
Guitar Amplifiers and Speakers:
All Hi Fi rules can be broken, and the breaking of the Hi Fi rules may be intentional.
Just my opinions.
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zintolo,
I never answered your question:
"Thanks for the personal experience, I've understood the issue with overdriven class A PP, but then what is the solution? Design PP in class AB only?"
No, there are excellent Class A amplifiers, and there are excellent Class AB amplifiers.
"Class A amplifier" does not mean the same thing as a "Class A Restaurant".
You can not get Ear Poisoned by a Class AB amplifier.
But a bad restaurant might give you food poisoning.
My first rule of listening to a Hi Fi stereo has always been:
If it sounds distorted to you the listener, then turn the volume down.
If it still sounds distorted, then it is time to troubleshoot.
Gross distortions:
A dirty needle on the cartridge, a worn record, a woofer voice coil that is rubbing, a woofer foam suspension that is falling apart, one of the push pull amplifier tubes has died, etc.
Less obvious distortions:
Your favorite amplifier can not properly drive that new speaker that has a very low impedance; a volume control is worn, and the wiper is not making good contact; The binding post has loosened on a speaker cable, and makes an intermittent/ohmic connection; etc.
Now, read my Post # 15 above. Hopefully it will be helpful too.
I never answered your question:
"Thanks for the personal experience, I've understood the issue with overdriven class A PP, but then what is the solution? Design PP in class AB only?"
No, there are excellent Class A amplifiers, and there are excellent Class AB amplifiers.
"Class A amplifier" does not mean the same thing as a "Class A Restaurant".
You can not get Ear Poisoned by a Class AB amplifier.
But a bad restaurant might give you food poisoning.
My first rule of listening to a Hi Fi stereo has always been:
If it sounds distorted to you the listener, then turn the volume down.
If it still sounds distorted, then it is time to troubleshoot.
Gross distortions:
A dirty needle on the cartridge, a worn record, a woofer voice coil that is rubbing, a woofer foam suspension that is falling apart, one of the push pull amplifier tubes has died, etc.
Less obvious distortions:
Your favorite amplifier can not properly drive that new speaker that has a very low impedance; a volume control is worn, and the wiper is not making good contact; The binding post has loosened on a speaker cable, and makes an intermittent/ohmic connection; etc.
Now, read my Post # 15 above. Hopefully it will be helpful too.
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An amp that can run AB1 is an AB1 amp. It is NOT a class A amp. Period.
cheers,
Douglas
Bandersnatch,
OK, you are technically correct . . .
But a lot of amplifiers advertised as Class A amplifiers, are really Class AB.
Marketeers at work.
Caveat Emptor.
OK, you are technically correct . . .
But a lot of amplifiers advertised as Class A amplifiers, are really Class AB.
Marketeers at work.
Caveat Emptor.
I never said all amps called Class A were, and it is indeed a big, steaming pile of marketing that tells these tales.
cheers,
Douglas
cheers,
Douglas
I would say it's class A until one of the tubes cuts off, then it's class B. Hence AB 🙂