I'm glad that you have found some "real" output transistors. The silicon in the dead one's looks tiny. It's been years since I peeled the lid off a 2N3055 but I seem to remember the silicon being bigger. When you were twiddling the pot I was cringing as the voltage readings were all over the place. The pot is most likely the reason for the failure. Fit the replacement bits and see what happens! You could fit a current limit in each power rail during testing. That will help further smoke escaping.
Yes, I know. I was also cringing but I didn't have any replacement pots at that time. In the mean time I've already worked a bit further on the amp and the next video should be a bit more positive. 😅
Die size is not a good indicator to verify if a transistor is fake. Newer 2N3055 versions have smaller dies compared with much older ones. I think they improved the heat transfer between the die and the casing in later generations. Long ago Motorola sold the 2N3055I which had a much larger die compared with the normal 2N3055.
Wow, seeing the insides of those two was very interesting. No amount of great Belgian beer can fix getting counterfeit transistors from a commercial seller. I look forward to the next chapter. I suspect the output causing the avalanche of failures like you do.
Among all the suggestions and hypothesis I'd watch out for the maximum voltage the output transistors will see between emitter and collector. Sometimes amplifier manufacturers specified transistors but selected versions of them a bit more capable. See if the transistors can withstand the full voltage of the power supply (from the - rail to the + rail). That applies as well to the drivers and VAS stage, for precaution.
i appreciate seeing this. recently had an amp that wouldn't come out of protect proceed to blow its power section in spectacular fashion while i was measuring the output mosfets. i suspect that one was marginal and chose the exact moment i reached for the power switch to turn off to go short. blew the circuit breaker and i felt like i'd had 10 cups of coffee.
Thanks. Yes, it was rather stressful and made me lose confidence in this project for a couple of hours. I guess it can happen to anyone, though. At least we have a nice video because of it.
The same thing has happened to me a couple of times over the last 20 years. It always seems to be totally unexpected and rattles my nerves for a half hour or so. I know how you feel.
Listening to the footage, it wasn't the bass but the first sharp transient that caused the fault. My guess is that the bond wire from the fake transistor blew open, and this caused a high voltage spike because of the output filter coil, which caused the chain reaction and destroyed the rest.
Hi Kristof. I'm betting those 2N3055s were fake. I've heard about fake components but as I mainly deal with valve gear I have never encountered any myself. You should ask Grahame (Radiocruncher) if he has encountered any. Great video, anyway. I liked the slow motion blow-up! Looking forward to the rebuild.
I'm glad that you have found some "real" output transistors. The silicon in the dead one's looks tiny. It's been years since I peeled the lid off a 2N3055 but I seem to remember the silicon being bigger. When you were twiddling the pot I was cringing as the voltage readings were all over the place. The pot is most likely the reason for the failure. Fit the replacement bits and see what happens! You could fit a current limit in each power rail during testing. That will help further smoke escaping.
Yes, I know. I was also cringing but I didn't have any replacement pots at that time.
In the mean time I've already worked a bit further on the amp and the next video should be a bit more positive. 😅
@@retro_tech I look forward to seeing it... No smoke this time!
Die size is not a good indicator to verify if a transistor is fake. Newer 2N3055 versions have smaller dies compared with much older ones. I think they improved the heat transfer between the die and the casing in later generations. Long ago Motorola sold the 2N3055I which had a much larger die compared with the normal 2N3055.
Wow, seeing the insides of those two was very interesting. No amount of great Belgian beer can fix getting counterfeit transistors from a commercial seller. I look forward to the next chapter. I suspect the output causing the avalanche of failures like you do.
You clearly underestimate the capabilities of a good Belgian beer. 😉
Among all the suggestions and hypothesis I'd watch out for the maximum voltage the output transistors will see between emitter and collector. Sometimes amplifier manufacturers specified transistors but selected versions of them a bit more capable. See if the transistors can withstand the full voltage of the power supply (from the - rail to the + rail). That applies as well to the drivers and VAS stage, for precaution.
Thanks for the suggestion!
i appreciate seeing this. recently had an amp that wouldn't come out of protect proceed to blow its power section in spectacular fashion while i was measuring the output mosfets. i suspect that one was marginal and chose the exact moment i reached for the power switch to turn off to go short. blew the circuit breaker and i felt like i'd had 10 cups of coffee.
Thanks. Yes, it was rather stressful and made me lose confidence in this project for a couple of hours. I guess it can happen to anyone, though. At least we have a nice video because of it.
The same thing has happened to me a couple of times over the last 20 years. It always seems to be totally unexpected and rattles my nerves for a half hour or so. I know how you feel.
Thanks! It was indeed a bit stressful. 🙂
Listening to the footage, it wasn't the bass but the first sharp transient that caused the fault. My guess is that the bond wire from the fake transistor blew open, and this caused a high voltage spike because of the output filter coil, which caused the chain reaction and destroyed the rest.
That's definitely also a possibility! Thanks for sharing your opinion!
Hi Kristof. I'm betting those 2N3055s were fake. I've heard about fake components but as I mainly deal with valve gear I have never encountered any myself. You should ask Grahame (Radiocruncher) if he has encountered any.
Great video, anyway. I liked the slow motion blow-up! Looking forward to the rebuild.
Thanks, Don! I sent a mail to the shop but no reply yet.
I'm looking forward to having this one fully restored too. It's a really nice amplifier.
most ST & Toshiba stuff circulating in open market are fakes.
You have 15mV on 3 ohm so it's 5mA! NOT 45 mA! 🙂
It's on 0.33 ohm. 🙂
My bad, I heard 3 ohm... Cheers!@@retro_tech