> he solid state transistor amplifier was invented, and they had no idea how it worked either.

That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works: like if we fiddle with the voltage at the base, we can influence the collector current, and all the rest.

What is true is that some early transistor designs of audio amps treated transistors like tubes: they featured a phase inverter transistor that fed two non-complementary push-pull stages whose output was combined by a center-tapped output transformer.

The excuse that well-matched complementary PNP transistors were not readily available at that time rings hollow, because it's possible to create an push-pull output stage with just NPN transistors. This is called "quasi complementary" (lots of search results for this).

Output transformers, if they have multiple taps in the secondary winding, do allow for different impedances. If the end users expect to be able to plug a 16 ohm speaker into a 16 ohm output jack and a 4 ohm into 4 ohm, then they will understand that kind of amp better.

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fsckboy 8 hours ago | parent | next [-]

>That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works

since everything that happens inside a transistor is exactly what is going on in a quantum sense, you've described "not knowing how it works". You cannot understand a bipolar transistor without quantum effects, it's the thing that creates the transistor effect.

the theory of amplifiers you go on to talk about was well developed at that time because it's the same theory for vacuum tubes.

	▲	kazinator 7 hours ago \| parent [-]
		You can empirically drive the equations that apparently govern the macroscopic behaviors, right down to details like temperature sensitivity, and the Early effect, without having a detailed model of what is going on at the atomic and subatomic level. Then what makes an amplifier work is explained by those equations. And for that not even the full detail of them is necessarily required, depending on what aspect of the amplifier we need to explain. Like basic operation versus concern for thermal runaway. What makes the amplifier work and what makes the transistor work are separate concepts. That's why understanding translates from tube circuits to transistors. A transistor circuit maybe an emitter follower, which has a counterpart in tube circuits known as the cathode follower. The cathode resistor creates local negative feedback similarly to an emitter resistor. Early op amps where tube circuits. They have the same differential input stage and the same basic theory of operation. You program their game the same way with resistors. The familiar Sallen-Key filter topology was first described with the help of tube circuits for reference, back in 1955. To undestand it, we don't even need the details like how amplifiers work at the component level except when we get into design parameters in which certain issues matter, like frequency-bandwidth product, or input offset current or whatever.

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kazinator 10 hours ago | parent | prev | next [-]

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!

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quickthrowman 10 hours ago | parent [-]

Sound masking systems still use 70V audio output with output transformers at each speaker, voltage drop is rough when your signal is only a few volts and you’re using small conductors. Last time I sold a sound masking install we used 14/2 cable for the 70V audio signal.

https://www.atlasied.com/speech-privacy-speakers?srsltid=Afm...

	▲	sethhochberg 10 hours ago \| parent [-]
		They're quite popular for distributed audio systems in general (of which sound masking is one type). "Constant voltage audio" comes in a few flavors and 70v is very common in the US, other parts of the world often use 100v. Background music systems in retail, voice paging systems, etc use constant voltage hardware because its much better technology for very long cable runs, daisy-chained speakers, and centrally located amplifiers. The cost is fidelity. Full-range audio transformers aren't cheap, so these systems usually make some compromises because your announcements or smooth jazz over the pasta aisle don't need to be true hi-fi. Its cool technology. Most of the speakers have variable power taps, so you can run a bunch of them in parallel on a single line and control the actual volume as-needed based on where the speaker is deployed by varying the transformer tap on each speaker.

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gizajob 10 hours ago | parent | prev [-]

*output transformers