One would be able to make a fair argument by saying that the "modern tube era" started with the 6L6. The metal cased version came first, then the glass one, followed by several upgrades and newer versions like the 7027 and 7027A. The 6BG6 and its variants were TV sweep tubes with 6L6 guts and a plate cap to keep the high voltage off of the base pins. Radio transmitters needed tubes too so the 807, 1625, and several others were created, all with 6L6 guts. There are even some directly heated versions like the 1624 (glass) and 1619 (metal). A tube first seen in the 1930's is still being made today and found in many of today's guitar amps, not to forget old McIntosh amps too.
There's a fascinating history there. The Beam Power Tetrode was developed as a reaction to the patents held on the European-designed Pentode. Simply put, RCA et al didn't want to pay Philips the licensing fees to build power pentodes, so they turned to the boys in R&D, resulting in the 6L6. The Beam Power Tetrode used a different mechanism to overcome the problem of Secondary Emission, and turned out to be more efficient as well. That's why there's so few Pentodes to be found among NOS Soviet tubes. They didn't care about the patent disputes, they chose the more efficient design.
4E27/8001/5-125/Gammatron 257B
Connect as triode, learn to re-getter, and treat as a 5V 845, but better because Eimac quality but cheap. Use two in parallel with filaments in opposite polarity to null AC filament IM products. Max B+ as triodes about +750 VDC, but run them (very) warm, preferably red.
All good fortune,
Chris
Connect as triode, learn to re-getter, and treat as a 5V 845, but better because Eimac quality but cheap. Use two in parallel with filaments in opposite polarity to null AC filament IM products. Max B+ as triodes about +750 VDC, but run them (very) warm, preferably red.
All good fortune,
Chris
Isn’t that also a beam tetrode type, as opposed to true pentode?
The $64,000 question is does it really make any difference? Do 6BQ5’s sound any more different from EL84’s than two brands of EL84?
If it has three metal thingies between the cathode and plate, I call them pentodes whether or not the third thingie from its sun is made of wire, or flattened metal. The 6JN6 is a TV sweep tube and therefore the third thingie is flat. Call it what you want. Some say beam tetrode, some say beam pentode, and some say beam power tube. Who is right?
Patent laws brought us some tubes that have almost identical specifications, but different constructions.
They did that so that Tube Rollers could have fun, Right?
Plug and Play:
For self biased tubes . . .
6BQ5 and EL84 (you can even find dual labeled tubes, but they either are Beam Power, or Pentode, they can't be both at the same time).
EL34, 6CA7, and KT77
6550 and KT88
Just be sure to connect Pin 1 to Pin 8 for the EL34 and the 6CA7.
And for self biased tubes, you generally can do Plug and Play . . .
6L6GC, KT66, and 5881
Caution: KT66 takes 0.4 Amps more filament current; So for . . . SE stereo 0.8 Amps, PP stereo 1.6 Amps more filament current.
Have Fun!
They did that so that Tube Rollers could have fun, Right?
Plug and Play:
For self biased tubes . . .
6BQ5 and EL84 (you can even find dual labeled tubes, but they either are Beam Power, or Pentode, they can't be both at the same time).
EL34, 6CA7, and KT77
6550 and KT88
Just be sure to connect Pin 1 to Pin 8 for the EL34 and the 6CA7.
And for self biased tubes, you generally can do Plug and Play . . .
6L6GC, KT66, and 5881
Caution: KT66 takes 0.4 Amps more filament current; So for . . . SE stereo 0.8 Amps, PP stereo 1.6 Amps more filament current.
Have Fun!
I tend to like more descriptive tube type names.
Beam Power, Beam Power Pentode, Kinkless Tetrode, . . . all of them have a Beam Former element. And yes, all of them have 5 Active elements.
Uh Oh! KT is not really a Tetrode, it has 5 active elements.
If you say to me . . . Pentode, I would appreciate it if you more accurately describe it as:
Either a Pentode with a Suppressor grid,
Or a Beam Power Pentode with Beam Former element.
And, of course, there are Beam Power Tetrodes (True Tetrodes), that only have 4 Active elements.
I used the 4-65A. The Beams are more accurately described as Sheets of electrons that make it through both the control grid and the screen grid, on their way to the plate.
How? Easy, both grids are birdcages, with identical numbers of vertical wires, and they are oriented so there are clear paths from the cathode, through both birdcages, to the plates.
Or, look at the 4X150A, same thing.
How they get a bird inside, I do not know. :>)
Beam Power, Beam Power Pentode, Kinkless Tetrode, . . . all of them have a Beam Former element. And yes, all of them have 5 Active elements.
Uh Oh! KT is not really a Tetrode, it has 5 active elements.
If you say to me . . . Pentode, I would appreciate it if you more accurately describe it as:
Either a Pentode with a Suppressor grid,
Or a Beam Power Pentode with Beam Former element.
And, of course, there are Beam Power Tetrodes (True Tetrodes), that only have 4 Active elements.
I used the 4-65A. The Beams are more accurately described as Sheets of electrons that make it through both the control grid and the screen grid, on their way to the plate.
How? Easy, both grids are birdcages, with identical numbers of vertical wires, and they are oriented so there are clear paths from the cathode, through both birdcages, to the plates.
Or, look at the 4X150A, same thing.
How they get a bird inside, I do not know. :>)
In fact there aren't too many differences in the characteristics from EL34. I assume thery're interchangeable as far as possible.
Best regards!
KT77 (JJ) Beam Pentode has more equally spaced curves than the EL37 or EL34. And better triode curves too.
And here is a tube you have never heard of, was on the $1 list years back. And it IS a real pentode with a fine spaced GRID3. 1st pic is with +24V on grid3, 2nd pic is with 0V on grid3. Good for 10 Watt with the +24Vg3 to reduce screen current. Very high gm also. (notice 0.15V grid1 steps) 3rd pic is triode mode.
4P1L is another real pentode, where +15V on grid3 improves it's pentode curves (below). 2nd pic is 4P1L with 0V on grid3. And last pic is 4P1L in triode mode. You won't be getting much 2nd harmonic with this triode.
And here is a tube you have never heard of, was on the $1 list years back. And it IS a real pentode with a fine spaced GRID3. 1st pic is with +24V on grid3, 2nd pic is with 0V on grid3. Good for 10 Watt with the +24Vg3 to reduce screen current. Very high gm also. (notice 0.15V grid1 steps) 3rd pic is triode mode.
4P1L is another real pentode, where +15V on grid3 improves it's pentode curves (below). 2nd pic is 4P1L with 0V on grid3. And last pic is 4P1L in triode mode. You won't be getting much 2nd harmonic with this triode.
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And the 6197 7.5 Watt pentode, an improved 6CL6 or 12BY7. No grid 3 fixup needed here. Got a big box of these for $0.35 each. Was a MIL contract sealed box. The whole box seems to be matched tubes. Must have cost Uncle Sam $$$$$$ These were nominally computer tubes. Best analog pentodes I've ever seen.
The 1E7G dual pentode in triode mode:
12HL7 10 Watt beam pentode in triode mode. High gm. Another $1 list alumni. No second harmonic around here either.
The 1E7G dual pentode in triode mode:
12HL7 10 Watt beam pentode in triode mode. High gm. Another $1 list alumni. No second harmonic around here either.
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Nice. How do they compare to say a good el34 (triode)
If I only need one, would I be looking at dc on the filament ?