These only have two said metal thingies between the cathode and plate. One with wire, one with flat metal. Not a pentode by any definition. Some are obviously just TV sweep tubes without a screen grid since there is an empty pair of holes in the mica spacers where the screen grid would go. With a GM of 50K to 65K and a Mu of 300 they make real good power oscillators and TV jammers when run continuously, which was not the intended mode of operation. I have a bunch of several flavors and have yet to tame any of them, but I have not tried UNSET yet. I laid out a 12 pin Compactron UNSET board but have not sent it out for fab yet.
The 6ER5 is listed as an RF Triode. But there is a shield that reduces the grid to plate capacitance. But that shield is Not referred to as a beam former.
The beam formers in a beam power tube, are there to form a beam. The formers purpose is not stated to reduce the grid to plate capacitance.
The screen is already there to reduce the grid to plate capacitance to extremely low values.
The 6EH5 is listed as an Audio Power Pentode. I see no reference to it being called a triode.
Frank [Frank's tube data] said it, not me.
The beam formers in a beam power tube, are there to form a beam. The formers purpose is not stated to reduce the grid to plate capacitance.
The screen is already there to reduce the grid to plate capacitance to extremely low values.
The 6EH5 is listed as an Audio Power Pentode. I see no reference to it being called a triode.
Frank [Frank's tube data] said it, not me.
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DAMN, that 6ER5 is nonlinear! And high enough (initial) mu to use in place of 12AX7 in a guitar front end. Would make a hell of a 2HD-generating, self compressing, soft clipper.
Might have just been implementation, and it was 40+ years ago now…. But I preferred the “sound” of the 50EH5 over the 50C5 when being used on those forum-banned line operated amps that ran with a B+ around 130 volts in SE. In order to get the 50C5 over the hump it needed more voltage, or run in push pull pairs.
The 6EH4 (not 5) is a big *** beam triode. Probably with the LX6/LW6 guts in it.
Might have just been implementation, and it was 40+ years ago now…. But I preferred the “sound” of the 50EH5 over the 50C5 when being used on those forum-banned line operated amps that ran with a B+ around 130 volts in SE. In order to get the 50C5 over the hump it needed more voltage, or run in push pull pairs.
The 6EH4 (not 5) is a big *** beam triode. Probably with the LX6/LW6 guts in it.
"The 6EH4 (not 5) is a big *** beam triode. Probably with the LX6/LW6 guts in it."
The 6EH4 is what became of the original 6BK4 high voltage shunt regulator tube when they tried to kill the X-ray emission these things made. These were short lived as the HV shunt regulator was moved to the primary side of the flyback where it works in the 1000 to 3000 KV range.
The 6EH4 has a maximum plate voltage of 36,000 volts and a typical plate current of 1 mA. The plate itself is a 2+ inch long thick cylindrical tube with the "target" at the far end. The cylindrical tube is for X-ray containment. While not specified here, the typical Mu of these things in in the 1000+ range while the Gm approaches zero.
The newer "primary side" regulators are like the 6HZ5 mentioned and pictured in post #17, a big sweep tube without a screen grid.
The 6EH4 is what became of the original 6BK4 high voltage shunt regulator tube when they tried to kill the X-ray emission these things made. These were short lived as the HV shunt regulator was moved to the primary side of the flyback where it works in the 1000 to 3000 KV range.
The 6EH4 has a maximum plate voltage of 36,000 volts and a typical plate current of 1 mA. The plate itself is a 2+ inch long thick cylindrical tube with the "target" at the far end. The cylindrical tube is for X-ray containment. While not specified here, the typical Mu of these things in in the 1000+ range while the Gm approaches zero.
The newer "primary side" regulators are like the 6HZ5 mentioned and pictured in post #17, a big sweep tube without a screen grid.
"I like - love 6AU5GT"
Then take a look at the 6AV5 in its various flavors. It has the same pinout, comes in a GT flavor (similar to the 6AU5 but slightly lower triode Mu), and a GA flavor (larger bottle with several different plate sizes that kept getting bigger over time), and the 6FW5 (only the large plate flavor of the 6AV5GA). All have the same pinout, and similar characteristics. All were derived from the 6BQ6GT which is similar, but has a plate cap.
Then take a look at the 6AV5 in its various flavors. It has the same pinout, comes in a GT flavor (similar to the 6AU5 but slightly lower triode Mu), and a GA flavor (larger bottle with several different plate sizes that kept getting bigger over time), and the 6FW5 (only the large plate flavor of the 6AV5GA). All have the same pinout, and similar characteristics. All were derived from the 6BQ6GT which is similar, but has a plate cap.
6F6 is one of the best pentodes you can find but it has become quite pricey nowadays.
It might not be appealing on paper with its moderate gm but, looking at all its specs together, it's very usable and effective in almost every application you can think of: pentode, triode, power tube in class A, AB1, AB2, driver and even preamp.....and great sound that in my opnion has also something to do with its cylindrical geometry. I prefer it to the 6V6 (which is a tetrode, oval plate) and many other pentodes.
My favourite (power) pentodes are: 6F6, ECL/PCL82, EL84 and EL34.
I have never looked at the EL37 as an interesting tube because it's always been highly overpriced. It might look aesthetically attractive but the EL34 has the same specs/performance. Why spend hundreds of $ when one can get the same perfomance out of a JJ EL34?
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I believe Real 6V6 are either called Beam Power Tubes, or called Beam Tetrodes.
(they are Not Tetrodes).
Real 6V6 have beam formers between the screen g2, and the plate.
Un-real 6V6 have Suppressor grids g3, between the screen g2, and the plate (but that would be a Pentode).
What is in a name?
Lots and Lots of confusion.
By the way, I like the JJ EL34 Pentode, but I was able to get more power and lower distortion from the JJ KT77 Kinkless Tetrode (AKA Beam Power tube).
(AKA: Also Known As)
My 1936 Philco AM / Shortwave Radio had a 6F6 SE output.
It had an 8 inch Dynamic Magnet speaker that went down to 100Hz or lower.
(they are Not Tetrodes).
Real 6V6 have beam formers between the screen g2, and the plate.
Un-real 6V6 have Suppressor grids g3, between the screen g2, and the plate (but that would be a Pentode).
What is in a name?
Lots and Lots of confusion.
By the way, I like the JJ EL34 Pentode, but I was able to get more power and lower distortion from the JJ KT77 Kinkless Tetrode (AKA Beam Power tube).
(AKA: Also Known As)
My 1936 Philco AM / Shortwave Radio had a 6F6 SE output.
It had an 8 inch Dynamic Magnet speaker that went down to 100Hz or lower.
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I keep seeing this claim, the 1624 is a DH "807", and I guess it's because the 1624 is identical in appearance to the 807. However, it ain't so. The 807 is a repackaged version of the audio final, the 6L6. The 1624 was designed as an RF final, and has a lowish plate current: Vgk= 0; IP= 130mA (less -VGK for Class C). You need to take the 1624 into Class *2 to get any meaningful output. The spec sheet even says so: for audio usage, the spec is a grid driver with a Zo <= 500R. These days, that's NBD as a MOSFET source follower can easily exceed that spec. In Class AB2 you'll get ~72W.
Did a project with the 6BQ6 after seeing it used as a 25W plate modulator in a QST article from the late '50's. This looked odd since that's where you'd expect to see a 6L6. No audio usage mentioned in the specs for the 6BQ6 (the most linear part of the plate characteristic is well within red plate territory) so did some loadlines. These looked real good, and I already had a junkbox OPT, and PTX that went well with it, and so why not? I increased the static bias well above spec: PD= 11W (Spec for TV HD duty); PD= 17.5W (as audio final) which improved the sonic performance. Seeing that the 6BQ6 is a HD final, the ratings are very conservative, and the spec bust doesn't impact service life in audio duty. Still on the original pair I used in Ought 7.
I have some 12AV5s that could be used in the same design in case anyone wanted the high voltage staying under the chassis. One thing you need to look out for is older 6BQ6 versions. The 6BQ6GA and 6BQ6GTB both work just fine. The sonic performance is outstanding. However, the 6BQ6GTA will go red plate with the same Q-Point. It even looks different, with a noticeably thinner cathode.
As for other pentodes, the TV HD and VD types are hard to beat. TV HD finals like the 6BQ5 can approach 100W with reasonable DC voltages. The 6LW6 (nearly unobtainium unless you get the ones with odd heater voltages designed for series strings in colour TVs that didn't include a PTX) can get you 100W+ with 350VDC, as opposed to the 800V you'd need to get the same output from a pair of 814s.
TV vertical deflection finals can get you ~35W, and some of these types already include triodes that can serve as grid drivers.
Back around 2000 I got to clean out a large warehouse where lots of old military surplus was left to rust, rot, or be destroyed by the vandals and druggies that occupied the place until the bulldozers came. I got to keep all the tubes that I wanted, the rest went into one of several large dumpsters. Broken tubes were everywhere. 833A's, 211's and 845's were smashed all over the place.
There were lots of broken "6L6 derivatives" for lack of a better term. I got to look at plenty of every flavor that was made up until the late 50's. The 1624 does have the exact same structure from the control grids outward as an 807 from the same vintage. The RF shielding that's seen in the 807 was found in some 1624's, and I have seen some 807's without the shielding. Both went through several changes during their run, and there were lots of different manufacturers who didn't all make tubes the same way. Yes, the operating characteristics of the same structure with two entirely different emissive cathodes WILL be different due to different geometries, and emission capabilities, especially in the peak current department. Oxide coatings improved over the years with at least one major quantum step upward in the 1960's.
I had some 1624's and could not get them to "rock" like an 807, so they wound up on my table at a hamfest where they were quickly snapped up. Apparently, they do work OK in some DHT (or DHP) applications, but I have some NIB 307A's that work much better.
Makers of "807's often stuffed the glass with whatever they had to fulfill government contracts. Sylvania was really good at this with the 6B4GA tube that had triode wired 6AV5 TV sweep tube guts inside. I found some rather unique looking "807s" with what looked like 7027A plates inside them. They would eat over 30 watts of plate dissipation with no hint of redness. Same guts that's found in some straight glass 6BG6GA tubes.
