Discrete audio amplifier project PT19 repair and a minor change

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@JohnAudioTech 5 жыл бұрын

Before someone calls me out, at 6:50, the emitters of the differential pair transistors are near 0v (~.7v) with a normally functioning amp. When the prototype amplifier had full +rail on the output, there was about 8v across the base to emitter on the right hand differential transistor.

@martinda7446 5 жыл бұрын

Excellent video. After working on a fair few DC coupled HiFi amplifiers - fault finding can occasionally send you bonkers, with every component having the wrong voltage on it, it can lead you a merry dance. The shift in gain from that transistor was fascinating. Transistors are often used with reverse biased base emitter junction to act as a zener.

@steveswan5714 5 жыл бұрын

Very interesting John 👍 I have a guitar amp that pics up a radio station when I adjust the guitar tone 😱 so I basically have a 100 watt radio😂

@listerine-pr5lt 5 жыл бұрын

I have seen in some Audio Amp they bind the two differential amplifiers pair transistors to each other with a simple common aluminum plate.

@kenhelix4494 2 жыл бұрын

Hi, I assume transistors within the same DIL package could be well matched, and they would certainly be at the same temperature. So why are they not used in audio amps?

@listerine-pr5lt 2 жыл бұрын

I wrote "I have seen that soloution" and why they do it you may ask them.

@joshhyyym 3 жыл бұрын

Wild idea, you could reverse bias transistor in order to match them. If you have one with slightly more gain than another, you could reverse bias it for a few minutes and regularly check the gain until it is the same as your other one. I don't know if it would have any other effects, though.

@bigbread9000000 5 жыл бұрын

I have been using the transistor tester on the cheap harbor freight meter to match my transistors, just like you heat from fingers throws off the readings!!

@ubergeeknz 5 жыл бұрын

If Snickers won't come to KZbin, KZbin comes to Snickers 😻

@davizord01 5 жыл бұрын

You damage the diode inside the transistor....ahhahhaha talking with the cat like a cat was the best part

@rich1051414 5 жыл бұрын

The diode? There isn't a seperate diode in the transistor, it is like two diodes pointing at each other, but they share the same silicone. Instead of NP doped silicone like a diode, its PNP or NPN doped silicone. So basically, 1 1/2 diodes make a transistor :P Though you are right ignoring semantics. You damage the doping in the silicone.

@bob4analog 5 жыл бұрын

So does reverse biasing the B to E junction damage the transistor? I wanted to use a transistor as a voltage reference for a power supply.

@pliedtka 5 жыл бұрын

Poor cat, 3 days by himself - must be very attached to you. The input transistor on the NF side gone. I think that's what killed my old Sima amp (50W per ch, but very high current 1000W in transformers) which was similar to Mr. Leach design - literally everything got fried VAS, voltage multiplayer, predrivers, drivers after the output section gave up when I was away. Maybe someone thought it was suitable for dance club, as I never learned what happened to it. I think of reusing the remains for D-class amp if I can get really good modules that run on +/-36V rails (Ice, Hypex) - I don't really need more 17-18dBW. If I can get magnet wire I could rewire the secondaries for more voltage - just an idea.