dear All
I like to remind a deveopment in the years 1932 / 1933 that is mighty interesting. Most valves at this moment could produce approx 20% efficiency of undistorted audio. Especially for battery equipment, there were investigations to improve this figure and prof. Barton in the USA did design a valve that was really diffent, the zero bias valve 46. This valve has 2 grids, but these are connected in parallel. The anode current at zero bias is than quite low. The idea was to drive these valves in positive grid voltages in order to increase the efficiency and drive the valve to high currents at low anode voltages. An other effect is quite clear and may be more interesting for us.
A valve has in the negative part of the transconductance characteristics a square law . More to the zero volts grid voltage, the characteristics become quite linear upto a big part in the positive region of the grid voltage, so the valve characteristics are surprisingly linear. But the disadvantage is that the grid start taking current, so there is a driving power required.
The results are quite amazing. A pair of simple 46 valves driven by a small power stage non biased without any resistor in the final, delivers 20 Watt at 70% efficiency, quite a difference with the 20% of a 45 Valve.
Further devolpments resulted in double triodes like the 6N6 wich can deliver 10 watts!!. In order to avoid the high driving power, valves were developped where a cathode follower wass included in the enveloppe directly connected to the grid of the zero bias valve. The valves were called tripple twin valves, delivered 3 times more power than a 45 and two times more that a 47.
AND...
The first amplifier for guitar amplification made by Fender used these triple twin valves.
---This sound made Fender famous!!---
I have a pair of 46 valves and a nice and big speaker from 1935 with electromagnetic bias. In future for sure will try to reproduce the fender amp
Friends, I think that it is worth experimenting with zero bias valves and listning how these will behave in audio amps. Must be quite different.
I hope to have contributed to many hours of nice experimantation
Regards
Nico
I like to remind a deveopment in the years 1932 / 1933 that is mighty interesting. Most valves at this moment could produce approx 20% efficiency of undistorted audio. Especially for battery equipment, there were investigations to improve this figure and prof. Barton in the USA did design a valve that was really diffent, the zero bias valve 46. This valve has 2 grids, but these are connected in parallel. The anode current at zero bias is than quite low. The idea was to drive these valves in positive grid voltages in order to increase the efficiency and drive the valve to high currents at low anode voltages. An other effect is quite clear and may be more interesting for us.
A valve has in the negative part of the transconductance characteristics a square law . More to the zero volts grid voltage, the characteristics become quite linear upto a big part in the positive region of the grid voltage, so the valve characteristics are surprisingly linear. But the disadvantage is that the grid start taking current, so there is a driving power required.
The results are quite amazing. A pair of simple 46 valves driven by a small power stage non biased without any resistor in the final, delivers 20 Watt at 70% efficiency, quite a difference with the 20% of a 45 Valve.
Further devolpments resulted in double triodes like the 6N6 wich can deliver 10 watts!!. In order to avoid the high driving power, valves were developped where a cathode follower wass included in the enveloppe directly connected to the grid of the zero bias valve. The valves were called tripple twin valves, delivered 3 times more power than a 45 and two times more that a 47.
AND...
The first amplifier for guitar amplification made by Fender used these triple twin valves.
---This sound made Fender famous!!---
I have a pair of 46 valves and a nice and big speaker from 1935 with electromagnetic bias. In future for sure will try to reproduce the fender amp
Friends, I think that it is worth experimenting with zero bias valves and listning how these will behave in audio amps. Must be quite different.
I hope to have contributed to many hours of nice experimantation
Regards
Nico
It was in a Dutch magazine about old radio's called 'the historic radio club'. I am planning to move to Costa Rica, so unfortunately I have all books already packed. I think that the amp was 1935
Have a great move, hopefully you can post the article once you unpack and settle down. My interest was piqued because I could not find a reference on any Fender amplifier that used the triple twin power tube...
In the first place, you don't have to work it in Class B. You can always bias into Class AB. Also, VTs don't have so wicked x-over behaviour as transistors (BJTs are better in this regard than power MOSFETs that can have really nasty x-over). These days, making use of types like this, and the RF zero bias triode finals, or the near zero bias power pentodes like the 814 or 1624, is a good deal easier than back in "the day" since you can use a source follower as the grid driver.
If these don't have that audiophool premium, and/or they're not unobtainium, might be worth looking into.
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.
This line of composite power tubes started in 1935 with the Triadyne 6B5. Here is the original manufacturer documentation, with very detailed data: http://frank.pocnet.net/sheets/201/6/6B5.pdf ; the evolution were the 6n6 (same tube but octal base, either glass or metal can: http://frank.pocnet.net/sheets/201/6/6N6MG.pdf ) and 6AB6G (automotive applications, http://frank.pocnet.net/sheets/201/6/6AB6G.pdf ). The optimal SE output transformer load impedence is 7Kohm; a 15V RMS input signal is required to get the full 5W rated output for SE operation.
I've done a bit of research about this tube in the past because it seems to require a minimal number of components to assemble a complete SE triode amplifier; I then put the project aside because it looks good on paper but there must be some flaw in practice: this tube family with the dual-grid output triode was never widely deployed and fell of out fashion very rapidly, in a matter of 5-6 years only. On my research, I only found a few small PA amplifiers and the Gibson guitar amp.
This line of composite power tubes started in 1935 with the Triadyne 6B5. Here is the original manufacturer documentation, with very detailed data: http://frank.pocnet.net/sheets/201/6/6B5.pdf ; the evolution were the 6n6 (same tube but octal base, either glass or metal can: http://frank.pocnet.net/sheets/201/6/6N6MG.pdf ) and 6AB6G (automotive applications, http://frank.pocnet.net/sheets/201/6/6AB6G.pdf ). The optimal SE output transformer load impedence is 7Kohm; a 15V RMS input signal is required to get the full 5W rated output for SE operation.
I've done a bit of research about this tube in the past because it seems to require a minimal number of components to assemble a complete SE triode amplifier; I then put the project aside because it looks good on paper but there must be some flaw in practice: this tube family with the dual-grid output triode was never widely deployed and fell of out fashion very rapidly, in a matter of 5-6 years only. On my research, I only found a few small PA amplifiers and the Gibson guitar amp.
Last edited:
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"...
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.
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.
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.
No worries... Here is the schematic for the earlier version of the Gibson EH-150 with the 6N6's:
An externally hosted image should be here but it was not working when we last tested it.
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.
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.
Attachments
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.
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.
Member
Joined 2009
Paid Member
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.