I'm looking for a LTSpice simulation on this. There are some around, but the use Triode mode, not Ultra Linear and mostly different tubes, Like KT66.
I want to start with the original design.
Any help ist welcome.
ThanX Winnie.
I want to start with the original design.
Any help ist welcome.
ThanX Winnie.
How about some actual measurements instead?
On the Skunkie YT channel you'll find a whole series of videos including initial tests and tests after modding. Scroll down a bit, it starts with an unboxing video and continues from there.
https://www.youtube.com/c/SkunkieDesignsElectronics/videos
Unless you have accurate detailed models of the output transformers, it is hard to get a simulation that is accurate.
In that case, use the same circuit, and insert a known accurate detailed model of another model output transformer.
For those that were avid readers of Bob Pease's 'Pease Porridge' column in EDN magazine, do you remember what Bob said about simulations.
In that case, use the same circuit, and insert a known accurate detailed model of another model output transformer.
For those that were avid readers of Bob Pease's 'Pease Porridge' column in EDN magazine, do you remember what Bob said about simulations.
Yes, i know that. But i do not want things like Skunkie did, there is negative feedback. I want to start at the beginning. Anyhow thX.
Several A10 simulation available on the net.
The "original" schematic (and the built amplifier) is dilettante construction (I have this, measured it, before I got apart), the OPT is the real "chinese" -cheap- c.ap.
It's a good approach:
The "original" schematic (and the built amplifier) is dilettante construction (I have this, measured it, before I got apart), the OPT is the real "chinese" -cheap- c.ap.
It's a good approach:
Well two things are missing, the tetrode_dd and trimmer. Can You help e again? ThanX a lot.
Download Stephie Bench models from tetrode:
https://www.intactaudio.com/forum/viewtopic.php?f=15&t=523
trimmer.asy:
Version 4
SymbolType CELL
LINE Normal 32 40 32 48
LINE Normal 16 32 32 40
LINE Normal 48 16 16 32
LINE Normal 16 0 48 16
LINE Normal 48 -16 16 0
LINE Normal 32 -32 32 -24
LINE Normal 32 -24 48 -16
LINE Normal 96 16 54 16
LINE Normal 62 10 54 16
LINE Normal 62 21 54 16
WINDOW 3 -118 -22 Left 0
WINDOW 123 -60 15 Center 0
SYMATTR Value Rvalue=100
SYMATTR Value2 position=0.5
SYMATTR Prefix X
SYMATTR Description A resistor trimmer, 0<position<1
SYMATTR SpiceModel trimmer
SYMATTR ModelFile control.lib
PIN 32 -32 NONE 0
PINATTR PinName T1
PINATTR SpiceOrder 1
PIN 32 48 NONE 0
PINATTR PinName T2
PINATTR SpiceOrder 2
PIN 96 16 NONE 8
PINATTR PinName WIPER
PINATTR SpiceOrder 3
https://www.intactaudio.com/forum/viewtopic.php?f=15&t=523
trimmer.asy:
Version 4
SymbolType CELL
LINE Normal 32 40 32 48
LINE Normal 16 32 32 40
LINE Normal 48 16 16 32
LINE Normal 16 0 48 16
LINE Normal 48 -16 16 0
LINE Normal 32 -32 32 -24
LINE Normal 32 -24 48 -16
LINE Normal 96 16 54 16
LINE Normal 62 10 54 16
LINE Normal 62 21 54 16
WINDOW 3 -118 -22 Left 0
WINDOW 123 -60 15 Center 0
SYMATTR Value Rvalue=100
SYMATTR Value2 position=0.5
SYMATTR Prefix X
SYMATTR Description A resistor trimmer, 0<position<1
SYMATTR SpiceModel trimmer
SYMATTR ModelFile control.lib
PIN 32 -32 NONE 0
PINATTR PinName T1
PINATTR SpiceOrder 1
PIN 32 48 NONE 0
PINATTR PinName T2
PINATTR SpiceOrder 2
PIN 96 16 NONE 8
PINATTR PinName WIPER
PINATTR SpiceOrder 3
I would think that her measurements of the stock unit might be helpful and more accurate than a simulation, even if you go in a different direction with your mods.
As I recall, she is fond of using Schade feedback rather than global and I think she left it in UL mode.
I've always read that, unless the output tube is a triode, or triode strapped, that some type of negative feedback is recommended in both regular pentode (or tetrode, beam or whatever) and UL mode.
Perhaps others here who are more technically minded will comment on the effect of running an EL34 in UL without any NFB.
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My opinion is not really to do the great things. But, talking about distortions and adding feedback, ignoring the not so good operating point of the input tubes, would not be my way. I will do the small things, like spend nearly 1mA to each tube in front, not only half of it.
Just to have another soldering iron, in before. ThanX for any help, Winnie.
ThanX a lot to the forum. Just run my first trial, it works. The results you can read after some time, but not the simulated ones, the results of interest are after soldering. Have a nice weekend, Winnie.
I have built 2 stage single ended amplifiers, with output either pentode or beam power tubes.
I tried it without any Negative feedback:
No global from output secondary to input tube
No UL mode
No 'Triode' wired mode
No Schade feedback, output tube plate to input tube plate
No Schade 'style' feedback, output plate to input tube cathode
No output transformer secondary to output tube cathode feedback
I am not aware of any other kind of negative feedback for a 2 stage SE amplifier.
I did not like what the no-negative feedback amplifier output looked like on a scope, when a pure sine wave was applied to the amplifier input.
I did not like the harmonic distortion and intermodulation distortion measurement results.
I did not like the sound of the amplifier.
For such an amplifier as above, I prefer either UL or 'Triode' wired mode; with the tradeoffs of those two modes:
Power output, Harmonic and Intermodulation distortions, and damping factor.
Just my experience and opinions.
Your mileage may vary
I tried it without any Negative feedback:
No global from output secondary to input tube
No UL mode
No 'Triode' wired mode
No Schade feedback, output tube plate to input tube plate
No Schade 'style' feedback, output plate to input tube cathode
No output transformer secondary to output tube cathode feedback
I am not aware of any other kind of negative feedback for a 2 stage SE amplifier.
I did not like what the no-negative feedback amplifier output looked like on a scope, when a pure sine wave was applied to the amplifier input.
I did not like the harmonic distortion and intermodulation distortion measurement results.
I did not like the sound of the amplifier.
For such an amplifier as above, I prefer either UL or 'Triode' wired mode; with the tradeoffs of those two modes:
Power output, Harmonic and Intermodulation distortions, and damping factor.
Just my experience and opinions.
Your mileage may vary
I run an A12 with Klipsch L Scala's, and like Nelson Pass told, the first watt is the most important, i would say, the first 100mW are the most important..... Therefore the choice of good operating points is essential. Let me play with Regards Winnie.
If you change first tubes cathode resistor to 1k, paralleled with 220uF, and EL34 cathode resistor to 360R (about 50..51mA anode current, instead of 40mA), the result will be a little better (lower distortion, theoretical power a little grater), but low B+ and small, mediocre OPT remains the limiting factor.
With this changes, this little amp would be a "bedroom amp", 1-2W output with tolerable distortion, and indicative bass.
With this changes, this little amp would be a "bedroom amp", 1-2W output with tolerable distortion, and indicative bass.
Yes, only reduce the input cathode resistor is not enough. it is also not bad to drive the power tubes a little bit hotter. I think the resistor should be 390 Ohm and the bypass should also be some more.
The 1KOhm Kathode resistor makes distortion a little better at lower levels, but also need a correction on the power tubes, 60mA would be fine.
I got 5W at less than 2% distortion with nice bass. The OT are surprisingly good for this cheap an amp and EL 34 tubes are quite easy to drive with one side of a 12AX7 all that is needed. The "first watt" was very clean with 0.4% distortion. This isn't rocket science but feel free to reinvent the wheel 🙂.
HiYa Stephe,
nice to meet you. Your "redesign" went also into the power supply, shorting the 10 Ohm fuse resistor and put an overall feedback from the output tube to the input tube. And yes, that reduces most of the distortions.
But, using only half of the input tube at the right operating point. i will start at the same point. But i will stop after biasing the output tube a little bit hotter, and bypassing some more the reduced cathode resistor. And yes, i know, there is much more i could do.
That is not reinventing the wheel, that's small corrections.
Anyhow i like your work. There should be more doing same.
Very best regards to you and Skunkie Designs Electronics from Winnie.
nice to meet you. Your "redesign" went also into the power supply, shorting the 10 Ohm fuse resistor and put an overall feedback from the output tube to the input tube. And yes, that reduces most of the distortions.
But, using only half of the input tube at the right operating point. i will start at the same point. But i will stop after biasing the output tube a little bit hotter, and bypassing some more the reduced cathode resistor. And yes, i know, there is much more i could do.
That is not reinventing the wheel, that's small corrections.
Anyhow i like your work. There should be more doing same.
Very best regards to you and Skunkie Designs Electronics from Winnie.
jan.didden,
You said: "Bob Pease also said a lot of sensible things, so don't judge him by that."
I agree. And I was not being critical of Bob in my earlier statement.
And Bob's remarks about simulations was actually one of his strong messages, and very sensible.
One person who just graduated in engineering school, asked what he should do to help him on his way to be an analog engineer.
Bob said something along the lines: 'have you been tinkering with circuits for years'.
Another reader asked how they took a brand new analog IC design and "optimized" it, after the first ones were produced.
Bob said something to the effect that they did not optimize it, they designed it from experience to work properly (predictive engineering).
You said: "Bob Pease also said a lot of sensible things, so don't judge him by that."
I agree. And I was not being critical of Bob in my earlier statement.
And Bob's remarks about simulations was actually one of his strong messages, and very sensible.
One person who just graduated in engineering school, asked what he should do to help him on his way to be an analog engineer.
Bob said something along the lines: 'have you been tinkering with circuits for years'.
Another reader asked how they took a brand new analog IC design and "optimized" it, after the first ones were produced.
Bob said something to the effect that they did not optimize it, they designed it from experience to work properly (predictive engineering).