Hi guys, this is my first post on the forum.
I want to ltspice my amp based on 6v6, but I don't have much idea, especially in the output transformers, I did what I could by copying some examples from the forum.
The original schematic is on this page, if anyone can give me clues on how to do it and test it.
https://diyaudioprojects.com/Schematics/DIY-Push-Pull-PP-6V6-Tube-Amplifier/
I leave you the file of what I did
it would be greatly appreciated
thanx a lot
I want to ltspice my amp based on 6v6, but I don't have much idea, especially in the output transformers, I did what I could by copying some examples from the forum.
The original schematic is on this page, if anyone can give me clues on how to do it and test it.
https://diyaudioprojects.com/Schematics/DIY-Push-Pull-PP-6V6-Tube-Amplifier/
I leave you the file of what I did
it would be greatly appreciated
thanx a lot
That is a very nice simple push pull amplifier.
It has good performance.
Why does anybody feel the need to Spice that proven Dyna design (other than to do it for a learning experience?).
Rather than Spice it, just build it.
You will learn a lot more building and testing, than Spicing-it teaches.
Learn a lot, when you check the wiring, power-up, and get the amplifier running properly . . .
Including adjusting the negative feedback parallel resistor / capacitor for best square wave response into a load resistor.
(With different output transformers, a little adjustment of that RC feedback network may be necessary).
Then Listen and Enjoy.
I have to apologize, Software and I do not get along: +
( + like the sign of the cross, just like when it gets used against Vampires).
It has good performance.
Why does anybody feel the need to Spice that proven Dyna design (other than to do it for a learning experience?).
Rather than Spice it, just build it.
You will learn a lot more building and testing, than Spicing-it teaches.
Learn a lot, when you check the wiring, power-up, and get the amplifier running properly . . .
Including adjusting the negative feedback parallel resistor / capacitor for best square wave response into a load resistor.
(With different output transformers, a little adjustment of that RC feedback network may be necessary).
Then Listen and Enjoy.
I have to apologize, Software and I do not get along: +
( + like the sign of the cross, just like when it gets used against Vampires).
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hahahahaha +
Thanks for your words, the amplifier was already built, I just wanted to do tests, such as where to put the grid stopper of the 12ax7, or see what happens if I remove the negative feedback etc etc. I don't have an oscilloscope, so it's hard for me to
Thanks for your words, the amplifier was already built, I just wanted to do tests, such as where to put the grid stopper of the 12ax7, or see what happens if I remove the negative feedback etc etc. I don't have an oscilloscope, so it's hard for me to
It sounds like you replaced the 6SL7 with a 12AX7.
As long as the amplifier is not oscillating, you are OK to try the following things:
The proper way to connect a grid stopper resistor, is to connect it directly to the grid tab of the tube socket.
The point is to have as short a wire as possible from the grid tab to the resistor (that reduces the series inductance, and also the stray capacitance to other parts of the amplifier.
[Getting a true and accurate Spice model of an output transformer is perhaps the most difficult task in all of Spice work.
Years ago at my work, I had a $50,000 Rohde & Schwarz Vector Network Analyzer (VNA), and $10,000 Calibration Set of shorts, opens, and loads.
I tested single ended and push pull interstage transformers, single ended output transformers, and loudspeaker cables (including Monster Cable, and 18 gauge zip cord).
Testing was done from 10Hz to at least 100kHz.
I also tested a balanced DSL transformer up to 6 MHz.
Then there was the testing of loudspeaker impedance versus frequency, and phase angle versus frequency.
I wish I could still use that test setup, but have no access to it after retirement.]
Go ahead and remove the RC negative feedback network, just try it and see. The damping factor probably will be about 1 (unity).
Then disconnect the screens from the output transformer's Ultra Linear taps, and then use 100 Ohm resistors from the screen to the same tubes plate (Triode Wired mode). The damping factor probably will be about 2, even without negative feedback.
Have fun trying those modes and settings, and have fun listening.
Then wire it back to original, listen again, and see what you think.
As long as the amplifier is not oscillating, you are OK to try the following things:
The proper way to connect a grid stopper resistor, is to connect it directly to the grid tab of the tube socket.
The point is to have as short a wire as possible from the grid tab to the resistor (that reduces the series inductance, and also the stray capacitance to other parts of the amplifier.
[Getting a true and accurate Spice model of an output transformer is perhaps the most difficult task in all of Spice work.
Years ago at my work, I had a $50,000 Rohde & Schwarz Vector Network Analyzer (VNA), and $10,000 Calibration Set of shorts, opens, and loads.
I tested single ended and push pull interstage transformers, single ended output transformers, and loudspeaker cables (including Monster Cable, and 18 gauge zip cord).
Testing was done from 10Hz to at least 100kHz.
I also tested a balanced DSL transformer up to 6 MHz.
Then there was the testing of loudspeaker impedance versus frequency, and phase angle versus frequency.
I wish I could still use that test setup, but have no access to it after retirement.]
Go ahead and remove the RC negative feedback network, just try it and see. The damping factor probably will be about 1 (unity).
Then disconnect the screens from the output transformer's Ultra Linear taps, and then use 100 Ohm resistors from the screen to the same tubes plate (Triode Wired mode). The damping factor probably will be about 2, even without negative feedback.
Have fun trying those modes and settings, and have fun listening.
Then wire it back to original, listen again, and see what you think.
Euro21,
The 6V6 is a Beam Power Tube.
Some data sheets have the correct diagram, some do not.
There is no Suppressor Grid (no 3rd grid).
Instead, we have Beam Formers.
There are too many different names that are used for a single device type, it confuses the issue.
For purposes of simplification (history, mind you), a directly heated filament, and a filament and cathode pair are considered to be One tube element.
A True Tetrode (both indirectly heated, and directly heated) has the following:
Filament
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
Or:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
Beam Power Tube:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Beam Formers
Plate
1,2,3,4,5
The beam formers only allow electrons from the cathode to flow to the plate in designed/prescribed shaped "Beams".
On some Beam Power tubes, g1 and g2 have exactly the same number of grid turns and grid wire spacing, this also creates "Sheets" of electrons.
Pentode:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Supressor Grid, g3
Plate
1,2,3,4,5
Just to confuse things a little more, look at a 4X150 Radial Beam Power Tetrode:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
The 4x150 construction uses a Bird Cage g1 and a Bird Cage g2.
The cage wires line up at exactly the same angle, so that the plate can Directly "see" the cathode through the perfectly lined up g1 and g2 wires.
The electrons travel from the cathode to the plate in "Beams" or "Sheets" if you want to call them that.
What is in a name?
More than often meets the eye.
Interesting?
An EL34 is a Pentode.
A KT77 is a Beam Power tube.
The specifications of voltage, current, transconductance, dissipation, g2 to g1 mu (u), etc. are almost identical.
It used to be that a 6BQ5 Beam Power tube, and EL84 Pentode had almost identical specifications.
So guess what the manufacturers did . . .
They Dual labeled them 6BQ5/EL84 or EL84/6BQ5.
That is cheating, and a blurring of the lines, only one manufacturing line, etc.
But it created more sales, and less requirement to stock 2 types of tubes.
The 6V6 is a Beam Power Tube.
Some data sheets have the correct diagram, some do not.
There is no Suppressor Grid (no 3rd grid).
Instead, we have Beam Formers.
There are too many different names that are used for a single device type, it confuses the issue.
For purposes of simplification (history, mind you), a directly heated filament, and a filament and cathode pair are considered to be One tube element.
A True Tetrode (both indirectly heated, and directly heated) has the following:
Filament
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
Or:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
Beam Power Tube:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Beam Formers
Plate
1,2,3,4,5
The beam formers only allow electrons from the cathode to flow to the plate in designed/prescribed shaped "Beams".
On some Beam Power tubes, g1 and g2 have exactly the same number of grid turns and grid wire spacing, this also creates "Sheets" of electrons.
Pentode:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Supressor Grid, g3
Plate
1,2,3,4,5
Just to confuse things a little more, look at a 4X150 Radial Beam Power Tetrode:
Filament and Cathode
Control Grid, g1
Screen Grid, g2
Plate
1,2,3,4
The 4x150 construction uses a Bird Cage g1 and a Bird Cage g2.
The cage wires line up at exactly the same angle, so that the plate can Directly "see" the cathode through the perfectly lined up g1 and g2 wires.
The electrons travel from the cathode to the plate in "Beams" or "Sheets" if you want to call them that.
What is in a name?
More than often meets the eye.
Interesting?
An EL34 is a Pentode.
A KT77 is a Beam Power tube.
The specifications of voltage, current, transconductance, dissipation, g2 to g1 mu (u), etc. are almost identical.
It used to be that a 6BQ5 Beam Power tube, and EL84 Pentode had almost identical specifications.
So guess what the manufacturers did . . .
They Dual labeled them 6BQ5/EL84 or EL84/6BQ5.
That is cheating, and a blurring of the lines, only one manufacturing line, etc.
But it created more sales, and less requirement to stock 2 types of tubes.
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ohhh thank you so much 6A3sUMMER!!!
I am going to try those changes that you tell me to see how it sounds.
Does the grid stopper go on the grid of the triode below the 12ax7? does the other 10k resistor in the other grid work as a grid stopper?
thanks for giving me something to play
Euro21 thanx a lot too!!
I am going to try those changes that you tell me to see how it sounds.
Does the grid stopper go on the grid of the triode below the 12ax7? does the other 10k resistor in the other grid work as a grid stopper?
thanks for giving me something to play
Euro21 thanx a lot too!!
Generic 6V6 spice model use tetrode symbol.
"
"
The #1 post asc use pentode symbol, which is unusable.
"
- Connections: Plate
- | Screen Grid
- | | Control Grid
- | | | Cathode
- | | | |
"
The #1 post asc use pentode symbol, which is unusable.
mrpunkk,
The 6SL7 dual triode, now you have a 12AX7 with two triodes, and it is the phase splitter stage.
If your amplifier is not oscillating, then you can get by without a grid stopper on the other grid.
However, just as explanation . . .
I believe that the 10k to the one grid works as a low pass filter to keep out supersonic frequencies, due to the Miller capacitance Effect of that grid to its plate. This could keep a fist rise square wave signal from having "ringing" at the amplifier output.
But If that 10k resistor is also intended to be a grid stopper, it needs to be right next to the socket grid tab, rather than an inch away or more.
The other 6SL7 grid, now 12AX7, does not have a grid stopper. If there was an oscillation, then I would put a 1k grid stopper and connect it right next to the socket grid tab (I definitely would not use a 10k grid stopper on that 2nd grid.
Grid stoppers are always connected directly to the grid, and the other end of the grid stopper is connected to the rest of the circuit (no other parts connected directly to the grid).
An important question for you:
Other than connecting the 12AX7 filaments, pins 4, 5, and 9 to work on 6.3 Volts, is your schematic Exactly like the schematic of the Link in Post # 1?
. . . Getting advice on a circuit that does not exactly follow the amplifier you have, is like blindfolding an Archer and asking him to hit the target bullseye.
The 6SL7 dual triode, now you have a 12AX7 with two triodes, and it is the phase splitter stage.
If your amplifier is not oscillating, then you can get by without a grid stopper on the other grid.
However, just as explanation . . .
I believe that the 10k to the one grid works as a low pass filter to keep out supersonic frequencies, due to the Miller capacitance Effect of that grid to its plate. This could keep a fist rise square wave signal from having "ringing" at the amplifier output.
But If that 10k resistor is also intended to be a grid stopper, it needs to be right next to the socket grid tab, rather than an inch away or more.
The other 6SL7 grid, now 12AX7, does not have a grid stopper. If there was an oscillation, then I would put a 1k grid stopper and connect it right next to the socket grid tab (I definitely would not use a 10k grid stopper on that 2nd grid.
Grid stoppers are always connected directly to the grid, and the other end of the grid stopper is connected to the rest of the circuit (no other parts connected directly to the grid).
An important question for you:
Other than connecting the 12AX7 filaments, pins 4, 5, and 9 to work on 6.3 Volts, is your schematic Exactly like the schematic of the Link in Post # 1?
. . . Getting advice on a circuit that does not exactly follow the amplifier you have, is like blindfolding an Archer and asking him to hit the target bullseye.
Euro21,
The original 6V6 was a Metal tube, and Pin # 1 connected to the Metal. The metal acted as a shield around all the elements of the tube.
The glass versions did not connect anything to Pin #1 (no shield)
All 6V6, metal and glass, connect the beam formers Internally to the cathode.
Manufacturers got lazy, and used a Pentode connection drawing instead of a Beam Power drawing.
I am attaching 2 photos of Correct Beam Power tube drawings for all to see.
The original 6V6 was a Metal tube, and Pin # 1 connected to the Metal. The metal acted as a shield around all the elements of the tube.
The glass versions did not connect anything to Pin #1 (no shield)
All 6V6, metal and glass, connect the beam formers Internally to the cathode.
Manufacturers got lazy, and used a Pentode connection drawing instead of a Beam Power drawing.
I am attaching 2 photos of Correct Beam Power tube drawings for all to see.
Attachments
Sorry if this is off-topic but euro21, where did you get that .asc file of Eli's PP EL84 amp? I'm curious because when I ran it, the results showed that the EL84 output tubes are run quite cold, with only 5.7W plate dissipation each, which is about half of the maximum. Does that look correct to you? I used the Ayumi N. 6BQ5 model in LTspice XVII. I'm not criticizing here, because the simulated results look very good indeed. I just want to make sure this .asc is what Eli intended. Thanks.
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I found this asc in my trash schematic collection, searching 1608 OPT.
The file date is from 2015. I don't know the amp working well or not, but simulation shows functionality.
p.s. I found in another directory the fixed bias version of this layout (I don't know if I was the "perpetrator" or not. 🙂 ). It's seems working at larger power.
p.s.2 I found the original source of asc:
https://www.diyaudio.com/community/threads/up-to-date-el-cheapo-schematic.108399/
The file date is from 2015. I don't know the amp working well or not, but simulation shows functionality.
p.s. I found in another directory the fixed bias version of this layout (I don't know if I was the "perpetrator" or not. 🙂 ). It's seems working at larger power.
p.s.2 I found the original source of asc:
https://www.diyaudio.com/community/threads/up-to-date-el-cheapo-schematic.108399/
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Thanks, I think that explains it.
I think there's nothing wrong with swapping 6BQ5/EL84 in place of 6AQ5/12AQ5, but the cathode bias resistor would need to be reduced in value for use with 6BQ5 outputs.
Anyhow, that's that for that.
For transformer models in LTspice, I like to use the transformer spreadsheet that Robert McLean contributed a while back, which has a good selection of transformers, and you can create a new model from your own measurements.
https://www.diyaudio.com/community/threads/spice-transformer-model-spreadsheet.181578/
BTW, it looks to me like Eli's circuit should work very well with 6BQ5 output tubes and a Hammond 1608 OPT if you change the value of R21 to 180R 3W. The originally specified value is 330R.
I think there's nothing wrong with swapping 6BQ5/EL84 in place of 6AQ5/12AQ5, but the cathode bias resistor would need to be reduced in value for use with 6BQ5 outputs.
Anyhow, that's that for that.
For transformer models in LTspice, I like to use the transformer spreadsheet that Robert McLean contributed a while back, which has a good selection of transformers, and you can create a new model from your own measurements.
https://www.diyaudio.com/community/threads/spice-transformer-model-spreadsheet.181578/
BTW, it looks to me like Eli's circuit should work very well with 6BQ5 output tubes and a Hammond 1608 OPT if you change the value of R21 to 180R 3W. The originally specified value is 330R.
6A3sUMMER
Disconnect the negative feedback, and it seems to gain some volume, I do not know if more quality in the audio. I reconnected the negative feedback and connected the 6v6 with triod mode as you told me, also add grid stoppers on the second screen of the 12ax7, I do not know if I am able to notice the difference in the sound, maybe something clearer and more controlled, but I think I'm guessing. How can I tell if the amp oscillates? I would hear it or feel it??, thank you for giving me so much to play and experience this Sunday
Disconnect the negative feedback, and it seems to gain some volume, I do not know if more quality in the audio. I reconnected the negative feedback and connected the 6v6 with triod mode as you told me, also add grid stoppers on the second screen of the 12ax7, I do not know if I am able to notice the difference in the sound, maybe something clearer and more controlled, but I think I'm guessing. How can I tell if the amp oscillates? I would hear it or feel it??, thank you for giving me so much to play and experience this Sunday
its exactly the same, Perhaps output transformers are not exactly the same as Hammond
mrpunkk,
Some times oscillations can happen without being easily observed.
Not having a scope makes it difficult to determine.
If the sound sometimes becomes distorted at normal volumes, perhaps there are oscillations that are bursted. The oscillating frequency can be beyond the audible range, but cause the music to distort during each burst.
Looking at your schematic, and the fact that you are enjoying the sound, your amplifier probably is OK.
Want to know more accurately about the performance of your amplifier? . . .
You need to invest in an entry level digital oscilloscope, a non-inductive power resistor, and a signal source.
I use a Denon Audio Technical CD C39-7147-EX. Frequency response, Harmonic distortion, 2nd and 3rd order intermodulation tests.
I have an inexpensive used function generator for the square wave tests; and the rise time, and fall time tests. it is not low enough distortion to test the amplifier harmonic distortion and intermodulation distortion.
Or,
Take the amplifier to a repair shop, and ask them to put it through its paces on their test bench.
Or,
Is there an Audio Club near to you (somebody will have the equipment needed to do the test).
Disconnecting Negative Feedback always raised the gain of an amplifier; unless there was so little gain to begin with that the amount of negative feedback dictated about the same gain.
Meanwhile, enjoy listening.
Some times oscillations can happen without being easily observed.
Not having a scope makes it difficult to determine.
If the sound sometimes becomes distorted at normal volumes, perhaps there are oscillations that are bursted. The oscillating frequency can be beyond the audible range, but cause the music to distort during each burst.
Looking at your schematic, and the fact that you are enjoying the sound, your amplifier probably is OK.
Want to know more accurately about the performance of your amplifier? . . .
You need to invest in an entry level digital oscilloscope, a non-inductive power resistor, and a signal source.
I use a Denon Audio Technical CD C39-7147-EX. Frequency response, Harmonic distortion, 2nd and 3rd order intermodulation tests.
I have an inexpensive used function generator for the square wave tests; and the rise time, and fall time tests. it is not low enough distortion to test the amplifier harmonic distortion and intermodulation distortion.
Or,
Take the amplifier to a repair shop, and ask them to put it through its paces on their test bench.
Or,
Is there an Audio Club near to you (somebody will have the equipment needed to do the test).
Disconnecting Negative Feedback always raised the gain of an amplifier; unless there was so little gain to begin with that the amount of negative feedback dictated about the same gain.
Meanwhile, enjoy listening.
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jcalvarez and rongon,
6AQ5 versus the EL84/6BQ5 is quite a bit different.
With a different g2/g1 mu (u); different transconductance Gm; different plate resistance, rp; 1.67X more filament current, what circuit parameters other than an adjusted bias voltage is needed? . . . . Lots!
Just changing the bias resistor or the bias voltage . . . is not going to give optimum performance of Both the 6AQ5 And EL84/6BQ5.
6AQ5 versus the EL84/6BQ5 is quite a bit different.
With a different g2/g1 mu (u); different transconductance Gm; different plate resistance, rp; 1.67X more filament current, what circuit parameters other than an adjusted bias voltage is needed? . . . . Lots!
Just changing the bias resistor or the bias voltage . . . is not going to give optimum performance of Both the 6AQ5 And EL84/6BQ5.
mrpunkk,
You are welcome.
I look at tube schematics every day. Sometimes I save them, but most of those get tossed out or lost.
Sorry, I do not have a treasure trove link / links of vacuum tube schematics.
I do have some schematics in my head (that I create/design, then build, test, and listen to).
I am trying to find the time and energy to open Threads and put the amplifiers on Tubes / Valves.
I only have 2 or 3 amplifier threads now.
I think my next one to start a thread on is my low power balanced amplifier.
I have not even completed the 2nd mono-block for Stereo listening. Soon? Perhaps
You are welcome.
I look at tube schematics every day. Sometimes I save them, but most of those get tossed out or lost.
Sorry, I do not have a treasure trove link / links of vacuum tube schematics.
I do have some schematics in my head (that I create/design, then build, test, and listen to).
I am trying to find the time and energy to open Threads and put the amplifiers on Tubes / Valves.
I only have 2 or 3 amplifier threads now.
I think my next one to start a thread on is my low power balanced amplifier.
I have not even completed the 2nd mono-block for Stereo listening. Soon? Perhaps