Wow 😯 just a slight increase by so little voltage and the result is 35% more current?Your welcomeI'll just add this to show you how the current can alter with a seemingly miniscule change in applied base voltage. So we can't use vbe as a means of adjusting anything and yet it remains one of the most useful measurements in fault finding.
If we increase the base voltage by just 0.01 volts we see an increase of 35% in the current in the 0.18 ohm resistor.
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That is impossible to answer because it depends what the actual device is.
If the devices are fake they can still fail under load. They may have an inadequate voltage rating and/or a low current rating. Its an unknown.
Genuine parts are always good. 99% of all failures only involve the outputs and drivers, in other words everything to the right of the bias generator.
I assume that when the vbe value is close to "turning on" the transistor and after this is what i should expect right? Minor changes in voltages great current increases. Wow
Amazing information. Thank you very much!!
Yes, it is not linear at all. Also remember that ultimately transistors like these are all 'current driven' and not voltage driven. The base/emitter voltage is something that occurs as you pass current through the b/e junction. The voltage will also level out at around (I know that's imprecise) at somewhere around 0.7 to 0.8 volts as you push more and more current through the junction.
Here is your Marantz as a working simulation. DC conditions (for the sim) as shown with bias set to 40ma and offset close to zero. Haven't tried it yet with a signal....
I'll post the file later and if you are interested enough to install LTspice you can click and run it and play around altering things.
2SC5200-A1943 are available here.https://www.tme.eu/gr/details/2sc5200/tranzistor-nrn-tet/toshiba/2sc5200-o-q/
PS just now i see that is to3pl case style
If you have another new one piece from soundservice supplier, try this using a test gear.
Eliot have a test gear for power transistors but Mooly can suggest you too .
https://sound-au.com/transistor-matching.htm
PS just now i see that is to3pl case style
If you have another new one piece from soundservice supplier, try this using a test gear.
Eliot have a test gear for power transistors but Mooly can suggest you too .
https://sound-au.com/transistor-matching.htm
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I haven't used this software before but it is amaziywgat you just did. I can run simulations and see what happens! Simply amazing thank you very much!!!
This thread will give you lots of info on LTspice but the file as it stands should click and run with nothing else needed.
https://www.diyaudio.com/community/...from-beginner-to-advanced.260627/post-4025305
https://www.diyaudio.com/community/...from-beginner-to-advanced.260627/post-4025305
Thank you for your information I really appreciate it. I see that those are the type o of "O" did you say i need the type "n" thta confuses me a little.
Also in the second link it states that i need to build a tester am i right? To match the transistors?
I'm not planning to buy a lot of them so that i gain match them. I will buy probably 5 of each so that i have 10 in total and measure gain (hfe). That's it for now.
Also I will do the test mooly suggested and see if i can get it to bias while on the dim bulb.
At this point and with the money and time i've spent on this project, this turned into a learning experiment.
Inhave already leraned a lot by troubleshooting this issue that i did not know before and i love it, even though iam unsuccessful.
So i will get it to bias with the transistors that are on now. See how long it takes to fry them again.
Remove everything and rebuild it with new ORIGINAL semiconductors and have a working amplifier.
The board has taken a beating with all the "magic" smoke and soldering and desoldering of components. But what the hell... at least i got to learn a few things about audio amps.. Not a bad deal after all...
I want to sincerely thank everyone for sharing your knowledge and your time.
I will return with results from "Mooly's Experiment" 😁😁😁 about the bias situation.
Pretty much anything will work in practice
the 5550 and 5401 are great default and they never blow up (in a sim) even at several kW dissipation.@alexpriftis85
You mentioned crossover distortion earlier. Here is the amp with zero bias at 1kHz and then 10kHz. The distortion is just visible in the first image but obvious at the higher frequency.
Both are functional at the moment. With zero bias:
On the left channel:
I replaced only the output transistors , the 4x 10ohm rsistors at their bases and the emitter 0.18ohm resistors , and checked all the way back to the differential amplifiers, everything checks out fine and are original parts.
On the right channel:
All transistors and most resistors apart from the differential amplifiers have been replaced with new ones including the 2sc2240 after the outputs.
Here it is at it's current state: