How Tube Amplifiers Work

it's a bit weird that I never thought about it before this, when I already had the facts in my head: the triode tube amplifier was invented by Lee de Forest, but he had no idea how it worked or even what it was capable of. then 45 years later, the solid state transistor amplifier was invented, and they had no idea how it worked either.

for people who have not had much EE education, what is important about triodes and transistors is that they amplify. you can put a signal in (a signal like from a microphone responding to your voice), and put some power in (like from a battery) and these amplifiers can make an output "copy" of the signal which is more powerful/"louder" than the original.

from this basic function, everything that we think of as "electronic" flows. we would still have electric things like light bulbs, heaters, spark plugs, electromagnets, but basically just electric steam punk frankenstein machines, and nothing subtle. Amplifiers are termed "active" electronics; without them, we'd simply have passive electricity.

I didn't read this article because I already know how these things work, and the article looks extremely confusing, and I've already read my fill of explanations that don't explain anything and (not saying this is one of those) I don't want to even risk that again. it is very difficult to find explanations for how transistors work that make any sense at all.

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I had a 1971 Marshall tube amp land in my lap, for free. I'm not a guitar player, but wanted to get it fixed it up before either selling it or learning guitar. There's a lot of "magic" there - the amp guy asked if I wanted to swap the tubes for some "more authentic" tubes that were used in England at the time. Pro tip - don't ask the internet for advice for making your tube amp sound nice, you'll get every opinion possible.

You don’t even need to ask! Generally speaking, you don’t want a guitar amp to sound nice, you want it to sound good, good being a function of many things.

For clean sound, use compatible radio preamp tubes and bias the power tubes conservatively.

For distorted sound, use the lowest overhead preamp tubes you can find, and bias the power tubes as hot as you dare without them breaking within the hour. You can always change them after a gig, or between sets. :-)

Radio Shack sold PA amplifiers with an output transformer well past the age of the tube, like the MPA series, e.g. MPA-40, a 20 W mplifier. On that thing you can obtain the raw amplifier output using the "70V" terminal. Then it has a number of through-the-trafo outputs labelled with nominal ohmages of speakers.

The Owner's manual extols the advantages of using transformers for speakers and describes how to use the 70V output in conjunction with external transformers.

Quote:

For complex multiple-speaker arrangements that require many speakers and long runs of connecting wire, we recommend you use a line transformer (not supplied), available at your local RadioShack store.

[...]

There are several advantages to using transformers.

• You can connect speakers with different impedances without causing differences in output between the speakers.

• You can add or remove a speaker without having to recalculate the entire system’s impedance.

• You can reduce signal loss when you use speaker wire over 50 feet long.

LOL!