Hi, longtime listener, first time caller.
I’m designing a teeny tiny guitar tube amp using Soviet subminiature 6N17Bs for the preamp stage. The datasheet lists two max anode voltages: Ua at 250 V, and directly underneath it, Ua at 350 V with a footnote “With tube cutoff, at Ia <= 5 uA”.
I think that means that with negligible current, the maximum voltage can be as high as 350 V.
I think this means that the load line on a plate current to voltage graph can be at 350 V when current is 0 A, as long as the operating range of the load line is below 250 V. However, I don’t want to fry any antique tubes with my assumptions.
Is the max plate voltage for a triode amplifier with this tube 250 V or 350 V?
Datasheet is here: http://www.tubeclinic.com/6N17B.pdf
Thanks!
I’m designing a teeny tiny guitar tube amp using Soviet subminiature 6N17Bs for the preamp stage. The datasheet lists two max anode voltages: Ua at 250 V, and directly underneath it, Ua at 350 V with a footnote “With tube cutoff, at Ia <= 5 uA”.
I think that means that with negligible current, the maximum voltage can be as high as 350 V.
I think this means that the load line on a plate current to voltage graph can be at 350 V when current is 0 A, as long as the operating range of the load line is below 250 V. However, I don’t want to fry any antique tubes with my assumptions.
Is the max plate voltage for a triode amplifier with this tube 250 V or 350 V?
Datasheet is here: http://www.tubeclinic.com/6N17B.pdf
Thanks!
A good place to start on a tube you are not familiar with is with the "electrical characteristics" operating point, kind of where the engineers designed the tube to work. So in your case 200V on the plate, 3.3mA plate current over a cathode resister of 325 ohms. This puts plate dissipation at 0.66W, nicely under the 0.9W limit that I assume is per plate, so 1.8W dissipation for both triodes.
If you want to move away from these conditions you will need to respect maximum ratings. As you raise plate voltage you will need to reduce plate current enough to keep under the plate dissipation limit. Depending on design constraints if you need a tube to work at 350V on the plate you might want to look at another tube. However the tubes are inexpensive so sometimes it's easier to experiment yourself. Get that plate cherry and back off a smuge and see how long it lasts.
Matt
If you want to move away from these conditions you will need to respect maximum ratings. As you raise plate voltage you will need to reduce plate current enough to keep under the plate dissipation limit. Depending on design constraints if you need a tube to work at 350V on the plate you might want to look at another tube. However the tubes are inexpensive so sometimes it's easier to experiment yourself. Get that plate cherry and back off a smuge and see how long it lasts.
Matt
Thank you, that’s helpful. I don’t specifically have a need to run it at 350 V, but I do want to explore how it sounds at different parts of its operating range without letting the magic smoke out. It sounds like careful experimentation is the way to go.
350 V is a limit on B+ for the amplification stage. Plate load resistor should be chosen to drop at least 100 V, so that plate voltage at the operating point does not exceed 250 V.
