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Old 10th August 2006, 10:49 PM   #1
phn is offline phn  Sweden
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Default Need 396A/6N3P/2C51/407A spice model

I have searcher here, as well as on google, for these models, like you should.

I have found a nice 407A-based line stage. I intend to post it here and let you guys have a say. But I want to play around with it in B2 Spice first. I try to learn B2 Spice as well as tubes.

I have Morgan Jones's Valve Amplifier laying around. I need to learn more about how to work with spice before I start reading it. If I'm to learn anything from the book and not get lost in the lingo and formulas and whatnots, I need a more hands-on approach. Otherwise it will be like reading a math book without solving the problems in it. Currently I suck pretty bad. I did one spice model, which didn't work. Got errors and it couldn't be fixed. When you tried to edit the model, Spice crashed.
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Old 11th August 2006, 03:54 AM   #2
arnoldc is offline arnoldc  Philippines
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Why not try the traditional way? Loadlines and stuff. If you have Morgan Jones, then that pretty much give you everything you need to know.

Why don't you post that 407A linestage and let's see...

FYI, I've made my own 407A pre and I really like it.
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Old 11th August 2006, 04:10 PM   #3
kevinkr is offline kevinkr  United States
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I think you have got it backwards I would start by reading as much of that Morgan Jones book as possible thereby getting a solid feel for how tubes actually work, and how to apply them in an actual circuit design or spice simulation.

On the Spice front start by downloading some good tube spice models from Duncan Monroe's website or search the threads here for spice models. Once you understand how some of these models work then perhaps you can successful create some of your own.

Incidentally unless you are running something like MCAP8 I find it is better to edit spice models in a text editor, and not spice itself. I use LTSpice (SWCAD3) free from Linear Tech. Works great with tubes and has no node or component limit. Has a somewhat steep learning curve if you are not conversant with spice, and you will have to create your own transformer models.

MCAP8 student/demo edition comes with a limited tube library that is easy to enable and as long as you don't exceed the node limit of 50 nodes the results are quite good.
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Old 11th August 2006, 05:42 PM   #4
phn is offline phn  Sweden
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I wasn't trying to be coy. I have no problem giving the people here the schematic. Here's the webpage. I believe it's the first page that turns up when you google 407A line stage.

Nobody would be happier than I if I could read Valve Amplifiers and learn something. Not only would I know tubes, but those five books on Java programming in my bookcase would mean I'm a crack programmer. I'm not. I can get things done, but I would never call myself a programmer. That my semester worth of object-oriented programming in college does. That way I don't have to lie.

The 22k resistor at the top of one of the tube halves in the 407A schematic sets the gain, I believe. It should be about 28 db. I could look up the name. I won't. That's just the point. I don't need to know what it's called. I only need to know what it does. Should I need to know it by name, I will learn it just as I eventually learned what a method, constructor, etc. are in Java. There's need to force it.

Even with a hands-on approach, I only expect a fraction of what Morgan Jones writes will stick. That's good enough for me. That will give me enough to build on. But just reading it, forget it. I will have read it. But I will have learned nothing.

I upload the schematic as well. It's 250VDC, I believe.
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File Type: jpg 407a.jpg (22.3 KB, 762 views)
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Old 11th August 2006, 11:32 PM   #5
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Person phn = new Person("phn");
try {
phn.read(Books.getAuthor("Morgan Jones").getBook("Valve Amplifiers"));
} catch (SlackerException ex) {
ex.printStackTrace();
System.err.println("Crack the darn book, then tell us what you think about it. It really is a good book.");
phn.dispose();
System.exit(-1);
} catch (SpiceCrashedException ex) {
phn.dispose();
System.exit(-1);
} catch (IWontLookupTheNameException ex) {
phn.dispose();
System.exit(-1);
} catch (INeverLearnAnythingException ex) {
phn.dispose();
System.exit(-1);
} catch (IAmNotAProgrammerException ex) {
System.out.println("Not everybody is.");
phn.dispose();
System.exit(-1);
}
phn.setIntelligence(phn.getIntelligence()++);
return true;
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Old 12th August 2006, 06:45 AM   #6
arnoldc is offline arnoldc  Philippines
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That schematic will run the first tube at 4mA and bias is at 4V via the 1K cathode resistor. The 22K plate resistor will yield around 160V at the plate of the 407.

ps.

And, yes gain is 28.6dB

PSRR is -14.4dB, Output impedance is 4.2K, 4.3Hz to 183kHz at -3dB
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Old 12th August 2006, 07:42 AM   #7
mach1 is offline mach1  Australia
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phn,

I would ditch the input capacitor, ditch the 1k resistor after the output capacitor and change the resistor from output capacitor to ground to from 100k to 1M.

While you are at it calculate an appropriate value for the output capacitor based on the following formula.

c = 1/ (6.283 r f)

where c is the capacitance in farads, r is the input impedance of your power amp in ohms, and f is the -3db frequency you are aiming for in Hz (commonly 5Hz, but you can put it lower if coincides with LF poles in your power amp).

Oversized coupling caps are costly in terms of $ and performance.

See Gary Kaufman's website for a build of the circuit. I believe he constructed it as per the circuit diagram.

Personally, I would go for this John Broskie circuit instead, which is extremely well thought out.

pm
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Old 12th August 2006, 09:57 AM   #8
arnoldc is offline arnoldc  Philippines
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Incomplete, my post...

Needs 60uF cathode bypass for the FR I gave and gain. Without it, 20dB of gain.

mach1, what is the diode for in JB's circuit? Any link to that?
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Old 12th August 2006, 11:38 AM   #9
phn is offline phn  Sweden
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ethermion, I have read the first chapter. Half I know about electronics I learned from that. So, yes, it's a very good book. It's probably as good as a book of its kind can get. But without some prior knowledge, I don't think it would be nearly as easy to read. The Square waves and transient section just went over me. It's not a long piece, but halfway through it everything I read was just noise. There was no revelation. No nothing. Total information overload.

By the way, I haven't read five books on Java. Nobody reads something like Java in a Nutshell. I have never learned anything useful from a book on Java, anyway. What I know about programming I have learned from hands-on experience and hammering it in. Don't mistake this for arrogance. But I have no real or genuine interest in programming (or math or electronics) so it has never come easy to me.

Quote:
Originally posted by arnoldc


PSRR is -14.4dB, Output impedance is 4.2K, 4.3Hz to 183kHz at -3dB
Cool. Z is a constant pain for me. PSRR I have to look up. It's not that it's the first time I see it mentioned. It's just that it's Greek to me.

Quote:
Originally posted by mach1
phn,

I would ditch the input capacitor, ditch the 1k resistor after the output capacitor and change the resistor from output capacitor to ground to from 100k to 1M.

While you are at it calculate an appropriate value for the output capacitor based on the following formula.

c = 1/ (6.283 r f)

where c is the capacitance in farads, r is the input impedance of your power amp in ohms, and f is the -3db frequency you are aiming for in Hz (commonly 5Hz, but you can put it lower if coincides with LF poles in your power amp).

Oversized coupling caps are costly in terms of $ and performance.

See Gary Kaufman's website for a build of the circuit. I believe he constructed it as per the circuit diagram.

Personally, I would go for this John Broskie circuit instead, which is extremely well thought out.

pm
I thought the 1k resistor, or a lower value, say 100R, would be beneficial. Just as the 100k. To quote Frank:

"What you're describing is due to the added gridstopper (more detail), the output R tames a mild overshoot (way above what's commonly believed being the audio band BTW) and the 100K pulldown resistor forces more constant current draw. The latter brings you better dynamic range, audibly so in most cases."

Most DIY pre/line stages have a 1M resistor on the output. I know I miss something fundamental here, but I thought the idea was to shoot for lowest possible Z. Other than what Frank wrote, it should also make the system less cable dependent.

The 5uF cap is indeed another thing that bothers me. I would like to use a more civil 2.2 uF cap, or less.

The circuit is Gary Kaufman's.

The Aikido does interests me as well. As does the 12A4-based line stage found in a long thread here.

I guess I was more surprised not finding a model than anything else. Thought the 396A/6N3P/2C51/407A (and equivalents CV2831, 6385, 6854, 6CC42, 18C51) would be popular enough.
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Old 12th August 2006, 05:32 PM   #10
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Default spice models

Here are 2 models you can try.

* 2C51 LTSpice model
.subckt 2C51 P G K
Bp P K I=(0.0104024146m)*uramp(V(P,K)*ln(1.0+(0.059315768 06)+exp((5.058207805)+(5.058207805)*((31.87419992) +
+ (-433.4177162m)*V(G,K))*V(G,K)/sqrt((11.5651995)**2+(V(P,K)-(16.01226163))**2)))/(5.058207805))**(1.510339782)

Cgk G K 2.2P
Cgp G P 1.1P
Cpk P K 1.0P
.ends 2C51



* 407A LTSpice model
.subckt 407A P G K
Bp P K I=((0.01444522184m)+(0.001093484804m)*V(G,K))*uram p((32.37781346)*V(G,K)+V(P,K)+(7.670441457))**1.5
+ * V(P,K)/(V(P,K)+(50.50181836))

Cgk G K 2.2P
Cgp G P 1.1P
Cpk P K 1.0P

.ends 407A

These are in the LTSpice flavour of Spice, since that is what I use personally. If they dont work in B2 spice then other versions can be provided. They were created using CurveCaptor.
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