Do we have to worry about reactive load as in RDH4?

[Alan0354]

I am reading how to draw the load line of reactive load. This is in page 30 to 33 of RDH4 chapter 2. You have to draw the ellipse, tilted ellipse as the load line and they go in circles!!! This is not easy to draw and tedious to calculate all the point of a reactive load.

Speaker is not exactly resistive. How do you deal with this? Do you actually draw this out or do you fudge it? Bottom line, is this important to learn? This book is for all tubes, all application. Here we only deal with audio amplifiers. I skipped the section of separate suppressor grid part as I never see any power tubes having this feature...........In fact, you can count all the power tube used in two handful!!!! 6L6GC, 6V6GT, EL34, EL84, KT88, 6550. Have I miss any?

Bottom line, I don't want to study anything that is not pertaining to audio amplifiers. This is not as if it's a useful technology that it worth the time anymore. Just trying to study the minimal to design amps.

[Austin]

I think there are spice models of tubes into inductive loads but I havn't tried it yet.

[Enzo]

Deciding what you "need" to learn before you know the subject is at least unfair to yourself. To design amps, you need to understand tubes. A non-audio circuit may just be ideal for making some piece of electronics more understandable. A subtle effect at audio might be a strong effect only at RF, but may serve as the example that connects to your mind. But gain is gain, shielding is shielding, and so forth.

EL34 has separate suppressor grid pin on base. Even if you only use tubes with internal G3 to cathode connections, understanding what that suppressor grid does might provide you some insights as to how screen currrents behave, and all those power tubes have screen grids.


You may want to learn about audio only, not RF, but the other side of that coin is that you probably don;t want your audio amp to be a good RF amplifer, nor do you want it picking up RF and detecting it. And understanding RF circuits is part of preventing unwanted RF activity. Realizing that what you may have THOUGHT was grounding was not grounding to an unwanted RF signal is part of the game.


I can't tell you which facts are "important" to learn. I doubt you or I will ever run out of memory, so to speak. The brain will store the things you don't "need" alongside the things you do.


Looking at elliptical load lines, I am struck by the likelihood that for most purposes a line drwn through the major axis of that ellipse will probably be sufficient for your needs. One needs to know that a speaker is not a resistor, it does have reactive qualities, but they are frequency dependent. As a rule we use the nominal impedance value of the speaker for calculations. Otherwise we would be left calculating a whole plot of impedance versus freq. The results might even look elliptical.

[J M Fahey]

Agree and add : you are right but the time honored design method is to design amps "as if" speakers were resistors.
By the way, "official" FTC or whatever power specification is measured using big resistors.
Truth behind that is that it's easier and repeatable for common folks like us all over the World, and amps so designed *do* work, after all.
One big exception where we can not ignore it is in SS amplifier protection circuits (which are quite complex and difficult to design).
The "simple" ones are not that safe and the "good" ones are real complex, specially because they self-trigger (doing their job) when amps drive very common speakers (specially woofers, close to resonance frequency).
There is not much consense even today.
As an example, Peavey (who had hired a Transistor Genius, Jack Sonderrnayer, ex RCA star Transistor Designer) uses *TWICE* the amount of transistors needed, just to play it safe.
The classic CS 800 power amp, 400+400W, uses 24 (yes, twenty four) metallic TO3 power transistors, mounted on massive, fan cooled heat sinks. How's that?

[Alan0354]

Thanks for the reply. I have a lot of things I need to study, not just tubes. I can only budget about two weeks all together for this as I am waiting for some of my pcb to come back. Actually I am an RF engineer specialize in transmission lines, electromagnetics, grounding and transistors design. I am not worry at all about the RF susceptibility issue as I spent a lot of time in signal integrity. That's the reason I am very pin point focused in learning one and only one thing.

I have to go back and revisit the suppressor grid. But I am more into a lower wattage amp which is mainly EL84, 6V6GT and 6L6GC. EL34 is not exactly on my radar unless there are some magic I can do with the separate suppressor. Is there any?

So people design using the speaker as a resistive load to do calculation? That will make things easy.

I know what you said about the need to study more completely and not by pick and choose. But I actually spending at least 3 hours a day six days a week in the last 10 years studying all the advanced math, EM, RF and all. I can tell you your mind can be filled up!!! I found myself forgetting other things in the middle of serious studying. Even my wife notice and she even asked me whether I damaged my brain with all the studying!!!! When you get old, you don't retain half as much as when you were young, that's life. I missed the days when I can read the text books once and remember enough to get a passing grade. It is scary to read back my own notes a few months later and have no idea what I wrote............it is my own hand writing but have absolutely no memory on the stuff. I still have so much more to study, I just started studying antenna theory last year for 3 months before got side tracked into music electronics. I intend to go back to it as soon as I finish this chapter of music electronics. This tube theory is only a very small part of my interest to get the job done, and I have no interest in any more than designing a power amp. Tube is not a dying technology, it's been dead for many years. Other than this narrow field of audio amplifiers, there is no more use for tubes anymore.

[Enzo]

Vacuum tubes are used in high power RF transmitters. I bet your microwave oven has a tube in it. The CRT has finally run its course, but not long ago at all, most video display was done on that large vacuum tube.

When you are cramming studies, sure you can forget things - details. But you retain more than you think. it is one thig to superficially learn some fact, it is something else to actually learn it and internalize it.

My post signature aside, I think back to the days I used to spend in the tavern. I played pocket billiards for hours. I had my basic game, and I was always working on learning new techniques. I'd practice putting english on the cue ball to get my caroms to take different angles, worked on masse shots, and so on. I found that hard as it might be to learn particular shots, if I put it all aside for a couple weeks or even a month, when I got back on a table, I no longer had my game plus some new shots, I simply had my game, and the new shots had become part of it.

[Alan0354]

Yeh, I remember the Klystron and TWTs. But have not seen them for a while. Transistors are getting better and better now a days. 35 years ago, I actually worked a little with Klystron, but I really don't know what I was doing at the time. Those Klystrons are big, we used it for satellite communication.

[Steve Conner]

I think you are too focused. Tube electronics is completely obsolete as you pointed out, that means that it is mainly used to mess around with for fun.

No tube amp designer (that I've heard of) ever worried about the reactive loads. Reactive loads cause excessive peak power dissipation, but tubes are very forgiving of that, because the big heavy plate averages it out even at the lowest audio frequency.

With the benefit of 50 years of hindsight, the main issue in guitar power amp design was surviving a too-high magnitude of impedance (such as a woofer at resonance) without burning out the screen grids. If you drove the amp into clipping with a highly reactive load, you could also generate big flyback pulses that would endanger the OT and tube sockets. Nowadays we can protect against that by putting flyback diodes across the tubes, but that wasn't economically viable in the 60s.

Those are the large-signal implications of a reactive load. The small-signal effect is that the impedance curve of the speaker interacts with the high output impedance of a tube amp, changing the frequency response of the system. You get a bass and presence boost compared to a solid-state amp, and you would never know about this if you only tested the tube amp on a resistive load.

[tubeswell]

As for obsolescence, as long as there are guitar amps, tubes will always be relevant.

[loudthud]

Those reactive load ellipses are single frequency fixed amplitude. If you want to see what really happends in a guitar amp, check this thread: http://music-electronics-forum.com/t28096/

Multiple frequencies and clipping make the load look like scrambled eggs. The biggest problem is that screen current can go very high when plate voltage dips close to ground or even goes negative due to reactive kicks from the OT or speaker.

[Austin]

You can build a highly reliable rf amplifier with only a few parts and one big honking tube that could put out alot of power vs. to do the same thing with ss you need lots and lots of delicate transistors in parallel correct? Sounds like tubes for the win. I am trying to do the opposite thing you are, that is learning all I can about tube audio so that one day I might be able work up to building a cool ham radio... Or at least some kinda linear amplifier for cb.

I do enjoy playing guitars for pool players in bars though...

[Steve Conner]

[Austin]

[ATTACH=CONFIG]19743[/ATTACH]

Hey is this the ultra super high voltage champ clone? hehe

[Steve Conner]

Yes, here's the OT for it.

[Austin]

Yes, here's the OT for it.
[ATTACH=CONFIG]19745[/ATTACH]

I want one. Think edcor sells em'? hehehe
Seriously there are some high power rf tubes on fleabay for less than 10 bucks I been thinking about trying to build an amp using one or two and a microwave oven transformer as a power supply.... I was going to try for a bass amp with another mot as the opt.