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The zero bias valve
The zero bias valve
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Old 18th January 2016, 04:19 AM   #11
jazbo8 is offline jazbo8
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The zero bias valve
Quote:
Originally Posted by pcan View Post
The model EH-150, one of the first Gibson guitar amplifiers, has a push-pull of 6n6 in the output stage. I don't remember any Fender with 6b5/6n6.
Thanks for clearing that up, so Fender never did use the 6N6, even if it did, I do not believe it was the model that gave us the distinctive "Fender tone"...
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Old 18th January 2016, 10:24 AM   #12
nicohfda is offline nicohfda  Spain
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Please tell me what a right handed triode is. Never heard that expression.
The crossover distorsion of zero bias valves is not that bad I guess. The tubes don't need bias, but that doesn't mean that the are at the cut-off point. Most are quite in the class A region when zerio bias is applied. Therefore you can also use them SE.
The nice thing is that the transconductance is close to linear around zero grid voltage.
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Old 18th January 2016, 10:26 AM   #13
nicohfda is offline nicohfda  Spain
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Quote:
Originally Posted by jazbo8 View Post
Thanks for clearing that up, so Fender never did use the 6N6, even if it did, I do not believe it was the model that gave us the distinctive "Fender tone"...
Thanks for the info
Unfortunately, I can't look up the article, I have already packed the magazines for the move to Costa Rica. So it may be my fault or an error in the magazine that Fender was quoted and not Gibson.
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Old 18th January 2016, 10:33 AM   #14
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The zero bias valve
No worries... Here is the schematic for the earlier version of the Gibson EH-150 with the 6N6's:

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Old 18th January 2016, 10:34 AM   #15
nicohfda is offline nicohfda  Spain
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Quote:
Originally Posted by pcan View Post
The model EH-150, one of the first Gibson guitar amplifiers, has a push-pull of 6n6 in the output stage. I don't remember any Fender with 6b5/6n6.
Hello Pcan
The main reason that the tubes fell out of fashion was the deveopment of the Penthode. With one pentode you have a tube less because you don't need power to drive it. That advantage was in general more economic that two valves and more power. At the end of the 30ties almost evrybody used penthodes for that reason. The zero bias was used a little longer for battery tubes due to the much higher efficiency.
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Old 18th January 2016, 10:36 AM   #16
ballpencil is offline ballpencil  Indonesia
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Quote:
Originally Posted by nicohfda View Post
Most are quite in the class A region when zerio bias is applied. Therefore you can also use them SE.
Am i misunderstanding what a "zero bias" is? To me, zero bias means Vgk = 0V. Now, attached is the 46 tube operating at my understanding of zero bias. With Vgk=0 and Vak=300V, plate current is 8mA. That's not much of class A isn't it? Hence, it's called class B there. Also, this low plate current is why we are reaching the aforementioned 70% efficiency, isn't it? Please correct me if i'm wrong.
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Old 18th January 2016, 11:04 AM   #17
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The zero bias valve
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Originally Posted by ballpencil View Post
With Vgk=0 and Vak=300V, plate current is 8mA. That's not much of class A isn't it?
To operate the 46 in class A, the second grid has to be connected to the plate similar to a pentode. So it can operate in both class A or B depending on the connection.
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Old 18th January 2016, 11:14 AM   #18
nicohfda is offline nicohfda  Spain
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Quote:
Originally Posted by ballpencil View Post
Am i misunderstanding what a "zero bias" is? To me, zero bias means Vgk = 0V. Now, attached is the 46 tube operating at my understanding of zero bias. With Vgk=0 and Vak=300V, plate current is 8mA. That's not much of class A isn't it? Hence, it's called class B there. Also, this low plate current is why we are reaching the aforementioned 70% efficiency, isn't it? Please correct me if i'm wrong.
For the 46 tube, you are right, the anode current at zero bias is approx 20 - 25% of the avarage Ia, so it will be class AB. The 6N6 however does operate in class A without any bias voltage applied due to the cathode follower inside the enveloppe, giving the output section positive bias.
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Old 18th January 2016, 12:15 PM   #19
ballpencil is offline ballpencil  Indonesia
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Ah i see. Thank you.
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Old 18th January 2016, 04:18 PM   #20
Bigun is offline Bigun  Canada
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The zero bias valve
Quote:
Originally Posted by jazbo8 View Post
To operate the 46 in class A, the second grid has to be connected to the plate similar to a pentode.
Making the 46 one of the most linear triodes ever made.
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