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On 19/02/2025 13:58, eewiz via
groups.io wrote:
I wish I would have stumbled upon this feature long ago.
?
This causes me to wonder about this wire probing
feature versus placing 0V sources in wires to measure currents?
The advantage of the 0V voltage source method is that it can easily
be used in the argument of B-sources.
--
Regards,
Tony
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On 19/02/2025 20:32, Carlo wrote:
TRAN 60 UIC or
"start external DC supply voltage at 0V" actually skip the ITS
step, hence even after 60 sec of simulation the time constant of
heater's model is such that that singularity is not reached.
This is not what "UIC" means or does. If you just want to start the
DC sources at zero, use the "startup" switch instead.
--
Regards,
Tony
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I have no problem understanding the possible multiple equilibrium
possibilities.
My question was why does my installation succeeds everytime in
finding a viable solution when it seems all others have problems.
Is my computer jinxed?
Le 19/02/2025 à 16:22, Andy I via
groups.io a écrit?:
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Show quoted text
On Tue, Feb 18, 2025 at 11:18 AM, Jerry Lee Marcel wrote:
How come that I can run the simulation, which gives
credible results?
A good question.
?
This model can fail because it has more than one stable
operating point.? Think about flip-flops.? They have two stable
states, and neither is guaranteed to happen initially.? A simple
flip-flop might come up in either state (and maybe one of three
states when simulated).
?
The heater's model is likely to always simulate coming up in
the same state because SPICE is deterministic, when used with
the same settings and algorithms.? But differences in simulator
settings or algorithmic details might change that.? I'm guessing
that is why you had better luck than others did.
?
Andy
?
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On Thu, Feb 20, 2025 at 02:44 AM, Jerry Lee Marcel wrote:
I have no problem understanding the possible multiple equilibrium possibilities.
My question was why does my installation succeeds everytime in finding a viable solution when it seems all others have problems.
Is my computer jinxed?
Sorry, could you be more specific about your viable solution of .TRAN analysis (without UIC or Startup flag) ? I'm referring in particular to the ITS (aka DC operating point) solution (e.g. the DC current entering the heater's pins). Thanks.
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Well, I have not much to tell.
The simulation worked right from day one, with 5.8V on the
heater.
However, just right now, running the simulation gave the same
erroneous results as mentioned by many, with 26V on the heaters
(weird from a 24V source).
BUT, running the sim for 60 seconds shows the voltage
oscillating, to more or less stabilize at about 5.8V. The peaks
never go above 15V.
I'm no expert, but I suspect the different timesteps explain the
different results.
Le 20/02/2025 à 12:19, Carlo a écrit?:
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Show quoted text
On Thu, Feb 20, 2025 at 02:44 AM, Jerry Lee Marcel wrote:
I have no problem understanding the possible
multiple equilibrium possibilities.
My question was why does my installation succeeds everytime in
finding a viable solution when it seems all others have
problems.
Is my computer jinxed?
Sorry, could you be more specific about your viable solution of
.TRAN analysis (without UIC or Startup flag) ? I'm referring in
particular to the ITS (aka DC operating point) solution (e.g.
the DC current entering the heater's pins). Thanks.
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On Thu, Feb 20, 2025 at 05:22 AM, Carlo wrote:
What do you really mean with "DC voltages look wrong" ? .TRAN 60 UIC skips the ITS step, hence there is not a DC solution at all.
What I mean is, what do the steady-state DC voltages look like, and are they correct or incorrect for your circuit?? I was not referring to the INITIAL voltages at the start of the transient simulation.? When the simulation is near 60 seconds and reached steady-state, do the bias voltages look right, or wrong?
?
Do you actually mean the average of the voltages on some circuit's nodes ? In this sense, yes, starting from about 50 sec, the (averaged) voltage on heater's pin looks good like the (averaged) current entering it (its sign looks good either !)
I meant the voltages in your circuit, at some or any or all circuit nodes.? Were the FET's gate and source DC (bias) voltages about right, when near 60 seconds?? Or were they wrong?
?
There is some feedback from the audio signal into the heater voltage.? Was that intentional?? Or just an undesirable side-effect?? I don't expect it would have very much effect on the heater's temperature (and from there to the triode's characteristics), but it looks undesirable to me.? Should there be filtering?
?
.TRAN 60 Startup analysis looks good either.
So, if .TRAN 60 UIC looks bad, but .TRAN 60 Startup looks good, then it should be obvious which one to use and which one to avoid.
?
But you added the word "either"!? I don't understand.? Did I misunderstand you?
AFAIK "Start external DC supply voltages at 0V" (Startup) does apply to DC voltage power supply and does not to SINE, PWL, PULSE, EXP sources including subcircuit (SUBCKT) sources. Does it apply to DC current power sources as well ?
Yes, "Startup" applies only to the DC value of independent sources.? I believe "sources" means both voltage and current sources.? (You can try it and see what it does.)
?
Note that it does not apply to independent sources inside of subcircuits.? That's why it has the word "external".? I believe LTspice does that because sources inside subcircuits are likely parts of models and how they work, and not the sources that supply power to the circuit.? LTspice wants to start only the main power sources at 0 and then ramp them up, but not modify what's inside the models.
?
Andy
?
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On Thu, Feb 20, 2025 at 05:22 AM, Carlo wrote:
BTW, as far as I can tell, below is the part of the tube's SUBCKT from dmtriodep.inc library modeling the heater:
(netlist code deleted for brevity)
?
Yes, that is the heater's model.? But there is also a "connection" from inside that netlist code, to the triode.? Presumably, that connection brings the heater's temperature to the triode, where it affects the triode's electrical characteristics.? I think many of the node voltages inside the heater model represent temperature, and there are thermal time-constants.
?
Andy
?
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On Thu, Feb 20, 2025 at 03:54 AM, Jerry Lee Marcel wrote:
However, just right now, running the simulation gave the same erroneous results as mentioned by many, with 26V on the heaters (weird from a 24V source).
Do you mean your .TRAN ITS solution (i.e. DC operating point) step returns 26V @ -166mA on the heater's pins ?
I'm no expert, but I suspect the different timesteps explain the different results.
A different timestep employed by .TRAN card for transient analysis can't explain that weird (non physical/nonsensical) result for the ITS solution.
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On Thu, Feb 20, 2025 at 05:44 AM, Jerry Lee Marcel wrote:
I thought I suggested small differences in (a) settings or (b) algorithms.? I do not suggest gremlins in the computer!? :-)
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Andy
?
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On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
What I mean is, what do the steady-state DC voltages look like, and are they correct or incorrect for your circuit?? I was not referring to the INITIAL voltages at the start of the transient simulation. When the simulation is near 60 seconds and reached steady-state, do the bias voltages look right, or wrong?
Ok, by "bias voltages" you mean actually the mean value of the voltages averaged for instance over a time period of the source signal (e.g. averaged over a 1ms interval for a 1Khz source signal). Near 60 seconds from the beginning of .TRAN 60 UIC analysis, the heater's voltage and current looks good.
?
I meant the voltages in your circuit, at some or any or all circuit nodes. ?Were the FET's gate and source DC (bias) voltages about right, when near 60 seconds? ?Or were they wrong?
Ok yes, for instance the MOSFET's gate and source mean (DC bias) voltages (and current) near 60 seconds look good.
?
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It's been discussed and argued, and stated by Analog Devices's experts with the LTspice code, that LTspice should be entirely deterministic, with no randomness in simulations unless the user actually adds it.? One of the tools sometimes used to solve systems of equations, is adding a little randomness into the mix.? The randomness can steer the solver one way or the other, thus potentially avoiding difficult solutions.? But we are assured that LTspice does not do that.? As far as I am aware, SPICE itself (from Berkeley) did not either.? As far as I know, "numerical noise" also does not exist in the sense that repeated runs through the same code should be exactly the same, down to the very last bit.? Even "round-off errors" are exactly predictable and repeatable.
?
If I remember correctly, ADI also said that LTspice code did have some unintended non-determinism, and that these have been (or are being) cleaned up in recent LTspice releases.
?
Over the years I have seen cases where LTspice simulated differently on repeated runs.? We know it should not have done that.? My guess is that I was witnessing some of those unintended bugs that ADI has been fixing.
?
Maybe they are not all fixed yet.? (And as they say, you can't get rid of ALL bugs.)
?
Or maybe you (Jerry Lee Marcel) had certain settings set, the first time you tried this simulation, which caused your simulation to converge correctly right "out of the box" the first time, but not a day later when you fired up LTspice again and it had reverted back to your default settings.? Who knows?
?
Andy
?
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On Thu, Feb 20, 2025 at 08:46 AM, Carlo wrote:
A different timestep employed by .TRAN card for transient analysis can't explain that weird (non physical/nonsensical) result for the ITS solution.
You're right about that.
?
Andy
?
?
?
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On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal into the heater voltage. Was that intentional?? Or just an undesirable side-effect?? I don't expect it would have very much effect on the heater's temperature (and from there to the triode's characteristics), but it looks undesirable to me. Should there be filtering?
Sorry, are you asking whether the audio signal feedback into the heater voltage comes from a design intentional choice ? Actually I don't know since I took it from the schematic of a commercial audio amplifier (Bravo Ocean).
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Carlo,
?
I am still confused.? Earlier you wrote that your output signal "doesn't look good at all" with .TRAN 60 UIC.
?
Later you wrote that .TRAN 60 Startup "looks good either".? Huh?
?
To me, they look exactly the same.
?
You also wrote that the "DC" (average) voltages near 60 seconds look right.
?
I am trying to determine whether the signals look good, or not good.? Can you please explain?
?
My thought is that if the average voltages look about right, then probably what you simulated is reasonably accurate, and "what you get is what you get" - meaning that if it looks bad, it probably really is bad.? If it's bad, maybe the circuit design is the reason.
?
Andy
?
?
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On Thu, Feb 20, 2025 at 06:30 AM, Andy I wrote:
My thought is that if the average voltages look about right, then probably what you simulated is reasonably accurate, and "what you get is what you get" - meaning that if it looks bad, it probably really is bad.? If it's bad, maybe the circuit design is the reason.
Yes, sorry for the confusion, you are right. The averaged voltages & currents about 60 seconds from the beginning of both .TRAN 60 UIC and .TRAN 60 Startup analysis look right. As you highlighted "what I get is what I get", maybe just the circuit design is the reason !
?
Thank you.
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On Thu, Feb 20, 2025 at 09:43 AM, Carlo wrote:
Yes, sorry for the confusion, you are right. The averaged voltages & currents about 60 seconds from the beginning of both .TRAN 60 UIC and .TRAN 60 Startup analysis look right. As you highlighted "what I get is what I get", maybe just the circuit design is the reason !
OK -- so the question still remains:
?
Does the output signal look "not good at all", as you claimed earlier?
?
Why do you say it doesn't look good?? What about it does not look good?
?
Admittedly it has more distortion, especially in the even harmonics.? But is it bad enough to not be acceptable?? The waveform looks good in a waveform plot, but human eyes are not good about spotting imperfections with our eyes.? Why do you say it is not good?
?
Andy
?
?
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On Thu, Feb 20, 2025 at 06:55 AM, Andy I wrote:
OK -- so the question still remains:
Does the output signal look "not good at all", as you claimed earlier?
I apologize, it was just a mistake/misunderstanding from mine.
?
Why do you say it doesn't look good?? What about it does not look good?
?
Admittedly it has more distortion, especially in the even harmonics.? But is it bad enough to not be acceptable?? The waveform looks good in a waveform plot, but human eyes are not good about spotting imperfections with our eyes.? Why do you say it is not good?
Yes, I can say that the output signal waveform looks pretty good (although its mean/average value changes slightly even after 60 seconds). Sorry, sometimes I'm in trouble with English :-(
?
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Le 20/02/2025 à 15:27, Carlo a écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal into
the heater voltage. Was that intentional?? Or just an
undesirable side-effect?? I don't expect it would have very
much effect on the heater's temperature (and from there to the
triode's characteristics), but it looks undesirable to me.
Should there be filtering?
Sorry, are you asking whether the audio signal feedback into the
heater voltage comes from a design intentional choice ? Actually
I don't know since I took it from the schematic of a commercial
audio amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to audio
signals.
It could result in distortion at very very low frequencies,
definitely out of the audio band.
Now this design is weird from the start. Choosing to power a tube
circuit from 24VDC is a major flaw, unless the goal is to create
distortion.
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I suspect that the weirdness is intentional.
Weird designs have existed from? the earliest day of DIY radio
receivers, before 'electronics'? was in the dictionary. I recall
a report of a circuit that had the 2 V lead-acid cell apparently
in series with the antenna circuit. Objective performance
measurements are typically not to be applied to such designs. DO
a web search for 'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry Lee Marcel
via groups.io wrote:
Le 20/02/2025 à 15:27, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal into
the heater voltage. Was that intentional?? Or just an
undesirable side-effect?? I don't expect it would have very
much effect on the heater's temperature (and from there to
the triode's characteristics), but it looks undesirable to
me. Should there be filtering?
Sorry, are you asking whether the audio signal feedback into
the heater voltage comes from a design intentional choice ?
Actually I don't know since I took it from the schematic of a
commercial audio amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to audio
signals.
It could result in distortion at very very low frequencies,
definitely out of the audio band.
Now this design is weird from the start. Choosing to power a tube
circuit from 24VDC is a major flaw, unless the goal is to create
distortion.
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
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On Thu, Feb 20, 2025 at 07:36 AM, Jerry Lee Marcel wrote:
Now this design is weird from the start. Choosing to power a tube circuit from 24VDC is a major flaw, unless the goal is to create distortion.
I'm not an expert. However I believe the LM317 in "current source" configuration actually fulfills two functions. First it is employed to bias the source of the IRF510 mosfet in common drain (aka source follower) configuration. Second such a constant current is employed to drive the 12AU7 triode heater.
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Tony Casey
Carlo
John Woodgate