Re: Anyone else get discouraged learning about tubes?
Yes, and I am curious as to how the different tube designs make use of these factors. Or more specifically, what was the reason behind the engineering that resulted in the different designs and their subsequently different tone characteristics.
I don't necessarily expect these questions to be answered in this thread.
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There are the different properties among triodes, pentodes, beam tetrodes, kinkless tetrodes if you don't might a bit of technical mumble jumble.
Triodes are used for preamp tubes and sometimes for power tubes. A triode only has three elements not counting the heater filaments: the anode (plate), the control grid and the cathode. Triodes produce a warm sound with even order harmonics when pushed into distortion.
Tetrodes. A tetrode adds an additional grid (actually a spiral helix of very fine wire) called a screen grid. The screen grid prevents spurious movements of electrons to and from the three main elements of the plate, control grid, and cathode when there is a large voltage swing on the plates. This reduces capacitance within the tube and makes the controlled, and wanted, movements of electrons more efficient. A triode will only produce about 1/2 to 2/3 as much power as a similar tetrode because with a triode the anode current is very dependent on the anode voltage. I know a lot of engineering speak but the bottom line is that a tetrode produces more power and sounds more punchy than a triode.
Pentodes. But tetrodes had a problem called the "kink". The kink was a kink in the curve of graph that plotted the relationship between anode voltage and the resulting anode current. This resulted in a nasty distortion artifact. The kink or distortion was caused by electrons jumping off the anode to the screen grid at the time the valve turns on and off with each cycle of the waveform. The solution was another grid (also another spiral helix of a special fine wire) called the suppressor grid.* The suppressor grid suppressed this unwanted electron jumping over to the screen grid. Thus the five main elements of the pentode: cathode, control grid, anode, screen grid, and suppressor grid.
Beam tetrode: Pentode tubes were the invention of Philips, a Dutch tube company, and they held the patent. Nobody else could legal build pentodes or at least call them pentodes with the exception of Mullard in England. Mullard was own by Philips. British engineers invented the beam tetrode as an alternative but didn't have the factory capability of building them properly. So RCA, which could build them, in the USA started building beam tetrodes for their British partners. This tube was the 6L6 introduced in 1933. The beam tetrode used a pair of beam forming plates to direct the beam of electrons past the screen grid in place of the suppressor grid as used in a pentode. Functionally the beam forming plates did the same thing as a pentode's suppressor grid, but by a different method. Other British companies couldn't legally call their own versions of beam tetrodes beam tetrodes, so they called them kinkless tetrodes or KTs.
There are some differences in terms of how they act in a guitar amp. A beam tetrode still has a little bit of kink compared to a pentode. This means that in practice a pentode, such as an EL34 or an EL84 will have more midrange complexity and detail. They also seem to drive easier making the amp seem to respond more quickly to subtle playing techniques.
Beam tetrodes produce less third order harmonic distortion than pentodes do when pushed, and with a stronger 2nd order harmonic, however. ( Triodes or triode connection yield the strongest 2nd order harmonics among tubes.)
* The number of turns, and the pitch of the turns, and so forth of these fine wire helix grids do effect the tone. Another factor is the material these wires are made from, such as molybdenum, thoriated tungsten, barium oxide coated...??
Grids are usually spiral helixes of very fine wire.
Cathodes are usually a small metal tube with a special coating in sound tubes. usually right in the center of the whole array.
Plates or anodes are metal plates with a special coating making the outside of the array.
Beam forming plates are made from metal plates and usually placed right inside the anode plates.
