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Old 5th November 2011, 09:33 PM   #11
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I have an Audio Experience preamp which uses 1 x ECC82 and 2 x ECC83s. I didn't like the slightly hard, strident sound of this preamp and I tried quite a few different ECC83s before I gave up and took a gamble and replaced them with Russian 6N3Ps (making the necessary alteration to the heater wiring). In this preamp these 6N3Ps sound great with no hard edge so I'm more than happy.
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Old 6th November 2011, 01:03 AM   #12
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Originally Posted by harwoodspark View Post
I have an Audio Experience preamp which uses 1 x ECC82 and 2 x ECC83s. I didn't like the slightly hard, strident sound of this preamp and I tried quite a few different ECC83s before I gave up and took a gamble and replaced them with Russian 6N3Ps (making the necessary alteration to the heater wiring). In this preamp these 6N3Ps sound great with no hard edge so I'm more than happy.
The 6N3P linearity at about -2V bias and 4 to 8ma current with up to 1 V peak input signal look very good to me :

Click the image to open in full size.

Alain.
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Old 6th November 2011, 03:40 AM   #13
TheGimp is offline TheGimp  United States
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IR LED bias works well with a current source anode load and 110V Vak.
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Old 7th November 2011, 04:07 AM   #14
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Originally Posted by TheGimp View Post
IR LED bias works well with a current source anode load and 110V Vak.
I discover with my spice simulator a LED bias alway make more distorsion then a bypassed cathode bias resistor ... The best is a simple cathode bias resistor with no bypass capacitor, the only price to paid is less gain.

Alain.
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Old 7th November 2011, 05:15 AM   #15
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Hello,
I believe that now is the time to make the transition from tubes to JFETs. Tubes have high distortion, operate at high dangerous voltage and are far too noisy. Peers seek Amperex 6DJ8 / ECC88 tubes because they are rare and expensive not because they make good amplifiers.
By any metric 2SK170ís make better amplifiers.
Or I guess as long as surplus Soviet tubes are cheep let them play.
DT
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Old 7th November 2011, 02:41 PM   #16
TheGimp is offline TheGimp  United States
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Alan, I found that in actual measurements the LED bias/Anode current source produced less distortion than bypassed cathode bias (6N1P-EV and 6N3P). I agree that unbypassed cathode bias would most likely produce less distortion than either. However, you are trading off gain for distortion.

I also have no doubt that it varies depending on tube type.

It is possible that a single stage with LED bias and Anode current source load may produce less distortion with sufficient gain where otherwise two stages with cathode bias unbypassed would be needed.

When the only tool you have is a hammer, everyting begins to look like a nail.

Spice simulators are nice to get in the ballpark. Measurements are better, and listening is best.
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Old 7th November 2011, 04:51 PM   #17
kevinkr is offline kevinkr  United States
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Originally Posted by DualTriode View Post
Hello,
I believe that now is the time to make the transition from tubes to JFETs. Tubes have high distortion, operate at high dangerous voltage and are far too noisy. Peers seek Amperex 6DJ8 / ECC88 tubes because they are rare and expensive not because they make good amplifiers.
By any metric 2SK170’s make better amplifiers.
Or I guess as long as surplus Soviet tubes are cheep let them play.
DT
Try to swing a couple of hundred volts peak to peak with one of your JFETs..

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out..
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Old 7th November 2011, 07:49 PM   #18
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Originally Posted by kevinkr View Post
Try to swing a couple of hundred volts peak to peak with one of your JFETs..

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out..
Take the output transformers out of it, where do you need to swing a couple hundred of volts? For a line stage like we are speaking of here more than a couple of volts may be too much.
The distortion spectra of triodes or JFETS depend on the bias point selected. JEFETís need not be biased to the flat end of their performance curves where they look like pentodes. The left hand end of the JFET curve family slope and look more like triodes and produce even, mostly 2nd, harmonics. It is all fun!

The point is that JFETís need friends too. That will leave more tubes to us diehards. I like 6BQ7ís and black plate 5670ís. The 5670 will roll right in the circuit in post number 1.

DT
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Old 8th November 2011, 01:07 AM   #19
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Originally Posted by TheGimp View Post
Alan, I found that in actual measurements the LED bias/Anode current source produced less distortion than bypassed cathode bias (6N1P-EV and 6N3P). I agree that unbypassed cathode bias would most likely produce less distortion than either. However, you are trading off gain for distortion.

I also have no doubt that it varies depending on tube type.

It is possible that a single stage with LED bias and Anode current source load may produce less distortion with sufficient gain where otherwise two stages with cathode bias unbypassed would be needed.

When the only tool you have is a hammer, everyting begins to look like a nail.

Spice simulators are nice to get in the ballpark. Measurements are better, and listening is best.
I am not crazy about LED bias but I'm a anode current source load fan ( like a DN2540 ). Since the only AC load is the grid leak resistor of the next stage, the gain is much higher and since the load line is more "horizontal", there is less distortion, specially for pentodes and JFET.

Sometime, preamp lower distortion is more important than high gain, all depend on the power amplifier and sources need. Many circuits need many tubes stages anyway, for example, if there is tones controls.

Not everybody own a good distortions analyser, there is some software ones working with the sound card but that's not very precise under 1% because average sound cards make more distortions than that ... I got some scopes home but it is difficult to visually evaluate small distortions with them.

Simulators can be very precise but most Spice models found on the net are not. I always generate the tubes and semiconductors curves with mine and compare them point to point with their datasheets curves, of courses, those curves are average for the parts types and sometime very differents from real parts but it is better than nothing ... Simulators are the best tools ever made for any kinds of electronic designs, I wish I have one when I build my firsts tubes amplifiers 40 years ago but the first DOS ones only appear in the '80's ...

Alain.
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Old 8th November 2011, 01:49 AM   #20
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Originally Posted by kevinkr View Post
Try to swing a couple of hundred volts peak to peak with one of your JFETs..

Actually there are plenty of tubes offering very high levels of performance without the hint of solid state that some of us here would find objectionable. I'm talking about tubes like the 5842, and triode connected 7721/D3A, 7788/E810F, and C3G. Yes less practical and more expensive than a 2SK170 but a bit more fun? Transfer function of JFETs is fundamentally pentode like which results in a different distortion spectra. (SITs are an exception, but expensive and hard to get.)

In any event this is the tube/valve forum where us tube diehards hang out..
Personnally, I will never use a field effect transistor directly in the "sound path" of a good quality tubes amplifiers, just as constant current source. Like you said JFET are not good for big voltage swing, so a power tubes driver have to be a tube too ... A power tube driver can be a high voltage MOSFET but it will usually be a poor quality hybrid circuit ...

JFET and MOSFET curves are similar to pentodes curves but that don't mean they produce the same sound, transistors commutation and thermionic effect in tubes are two very different principles.

Alain.

P.S. I wonder why so many peoples talk about the 2SK170 like if it was a "magic" JFET ... It is just a popular myth, they are not very linear and not fantastic in a common source amplifier stage ... And there are so many others much cheaper to discover ...
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