Beginner's guide to vacuum tube amplifier design

[gamato]

Dear all,
I hope this might be of interest here.

I recently put together a beginner's guide to vacuum tube amplifier design. I would be happy to share it with you.

You can read the full text from here: https://www.vtadiy.com/book/

Thanks in advance for any suggestions or criticisms.

Giuseppe

[vampwizzard]

looks extensive! your english is pretty good as well. Thanks for putting this out in the world!

[PRR]

At a glance: pretty good stuff.

_I_ would skip "tetrodes". TRUE tetrodes were a stepping-stone, yes. But they were never commonly used in audio amplifiers, because Pentodes and "Beam Power Tetrodes"(*) came right after. Tetrodes have problems, solved by the pentodes. Treating tetrode problems just confuses people who do not understand that all we use are pentodes.

Yes, True Tetrodes lingered in VERY high-power radio applications. Basically 2,000V and up, where a 500V screen voltage is not a real limit.

(*) "Beam Power Tetrodes" was a name to dodge the patent on Power Pentodes. Instead of a "grid 3" these have side-electrodes at the same place for the same reason. On the drawings, the patent examiner saw "different". Inside the tube, the electrons feel the same effects. Main effect being to suppress the trouble at Vp<Vg2.

While the earliest Power Pentodes and the early "Beam Power Tetrode" tended to have different curves, all of this was designable. While EL34 is still a soft pentode and 6L6 is still a hard beam-power tube, some others have been built both ways under the same type number, often depending what tooling the factory has handy rather than any fundamental technology.

[PRR]

https://www.vtadiy.com/book/chapter-2-vacuum-tube-basics/2-1-hydraulic-valves-as-a-metaphor/

I love the valve analogy.

I wish it were animated. I guess that would not work in the printed copies. (Even here, the thumbnail doesn't animate.)

[jjasilli]

Agreed, but, as long gamato asked:  I'm intrigued by the intensity concept:  "the intensity of the water flow, through the pipe, follows the signal-controlled position of the valve."

Intensity usually means power = Watts??? The tube is a voltage amplifier.  Voltage = pressure which might also mean intensity???  I guess as the signal voltage swings at G1 there's a small swing in Watts (assuming the current remains constant at that signal setting).  But I think the swing in Watts is insignificant; its the larger transconductant voltage swing at the plate that matters. 


Anyway I think the use of the word intensity might be explored.  Please feel free to jump in.

[shooter]

anything that lights the bulb is good, while I like equating, as a nubbie at something I've found grasping the actual "thing" as a stand-alone, keeps the light going, then equating nails it down.
schematic reading is a good example, put the layout in a drawer til you become reasonably proficient at schematics, then open the drawer.

[davidwpack]

I=Amps=INTENSITY of current.   ?

[gamato]

Hi all,
Thanks for your suggestions.

@jjasilli: A tube basically modulates the "intensity of current" via g1. A tube forms a voltage amplifier just when a load is connected to the anode. Without load, you just see a (possibly minor and useless) current variation at the anode. I discuss this in Section https://www.vtadiy.com/book/chapter-3-vacuum-tubes-as-amplifiers/3-1-voltage-and-power-amplifiers/.

@PRR: Initially I considered not to introduce tetrodes. However, I needed somehow to describe the use of the screen grid and this brought me to tetrode. Consider however that, when you use a pentode, you generally forget about the suppressor (which is by default connected to the cathode) and you in fact treat it as a tetrode in your schema . In any case, I agree that someone might get confused. I will try to merge tetrode and pentode again or, at least, to point out that tetrodes are never used in audio. I also did not introduce Beam Power Tetrodes, just not to make things more confusing... Again, you practically treat and see them as tetrodes/pentodes.

Thanks again
Giuseppe

[gamato]

By the way,
@PRR I like your valve animation
Giuseppe

[jjasilli]

Thanks gamato!  I can't believe I didn't get that before: the signal voltage on G1, through transconductance, causes the current in the tube to vary, which causes a larger voltage swing across the load on the plate.

I now see that your intensity statement is correct as written:  "the intensity of the water flow, through the pipe, follows the signal-controlled position of the valve." Because, Flow = Current.