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03-14-2025, 01:30 AM
(This post was last modified: 03-14-2025, 01:32 AM by soundmasterg.)
Hi Kevin,
I'm in my early 50's now.....getting old.
I recalled something saying the 6L6 has been in continuous production somewhere around the world since 1936, and I know that has beam forming plates, so that is why I was saying the 30's.
Some of the small 9 pins sound closer to a 6V6 than an EL84 like the 6973 or the 6CM6 for example. I like the chime and nice mids of the EL84 but I quickly start missing the bass that other tubes have like the 6L6 or even the 6V6 or 7591. Actually my favorite power tube is probably the 7591/7868 because it has almost as much gain as the El84 for a power tube, but it has a more even frequency response. Since it has a lot of self gain, you don't need to hit it with a large gain out of the preamp, and if you use a suitable phase inverter, then it can really overdrive the power tubes. In an amp I made for myself, I used a LTP circuit for the phase inverter, but I used a 12BZ7 instead of a 12AX7 to hit the power tubes really hard. It has the same gain as the 12AX7 but half the output impedance so it drives the power tubes twice as hard. They're pretty cheap too for NOS. They can be microphonic, especially if used in V1, but in the PI they seem ok.
Here are some links for the vacuum transistors for anyone who might want to know more about them. I think they were made primarily for space applications as they don't have any issues with radiation like traditional transistors do (FETS and BJT's) and the first prototype was able to transmit into the lower middle of the terahertz gap which is beyond transistors, and from what I understand, tubes can still get a bit higher, but it is impressive. The first prototype also had no degradation of performance up to 200 degrees C, which is very impressive. They figured out in the last couple years how to make them bipolar also, which greatly expands their use possibilities.
I've worked at Intel in the last decade (until I was laid off anyway) and have some experience with traditional computer devices. They've almost reached the physics limits of MOSFETs in processors, so there will have to be something new to continue Moore's Law, and these vacuum transistors are one of the possibilities. Of course I'm interested to see if they would work for audio.
Greg
https://spectrum.ieee.org/introducing-th...of-nothing
https://pubs.acs.org/doi/10.1021/acs.nanolett.6b04363
https://engineeringcommunity.nature.com/...transistor
https://physicsworld.com/a/nasa-scientis...ransistor/
I'm in my early 50's now.....getting old.
I recalled something saying the 6L6 has been in continuous production somewhere around the world since 1936, and I know that has beam forming plates, so that is why I was saying the 30's.
Some of the small 9 pins sound closer to a 6V6 than an EL84 like the 6973 or the 6CM6 for example. I like the chime and nice mids of the EL84 but I quickly start missing the bass that other tubes have like the 6L6 or even the 6V6 or 7591. Actually my favorite power tube is probably the 7591/7868 because it has almost as much gain as the El84 for a power tube, but it has a more even frequency response. Since it has a lot of self gain, you don't need to hit it with a large gain out of the preamp, and if you use a suitable phase inverter, then it can really overdrive the power tubes. In an amp I made for myself, I used a LTP circuit for the phase inverter, but I used a 12BZ7 instead of a 12AX7 to hit the power tubes really hard. It has the same gain as the 12AX7 but half the output impedance so it drives the power tubes twice as hard. They're pretty cheap too for NOS. They can be microphonic, especially if used in V1, but in the PI they seem ok.
Here are some links for the vacuum transistors for anyone who might want to know more about them. I think they were made primarily for space applications as they don't have any issues with radiation like traditional transistors do (FETS and BJT's) and the first prototype was able to transmit into the lower middle of the terahertz gap which is beyond transistors, and from what I understand, tubes can still get a bit higher, but it is impressive. The first prototype also had no degradation of performance up to 200 degrees C, which is very impressive. They figured out in the last couple years how to make them bipolar also, which greatly expands their use possibilities.
I've worked at Intel in the last decade (until I was laid off anyway) and have some experience with traditional computer devices. They've almost reached the physics limits of MOSFETs in processors, so there will have to be something new to continue Moore's Law, and these vacuum transistors are one of the possibilities. Of course I'm interested to see if they would work for audio.
Greg
https://spectrum.ieee.org/introducing-th...of-nothing
https://pubs.acs.org/doi/10.1021/acs.nanolett.6b04363
https://engineeringcommunity.nature.com/...transistor
https://physicsworld.com/a/nasa-scientis...ransistor/
