Help: Noise from one channel during startup

[Mooly]

Either the MJE's or BD's would be fine. Given a choice I would probably take the MJE's. I mentioned both those because they should be universally available. Although they look very different spec, wise both are fine in practice.

BC546 not 456.

I've never heard or come across a "G" version of the 2N5551 but a quick look shows it to be just a lead (as in Pb) free device, so no problems there.

 

[dungdochi1978]

Hi Mooly,

Thank you for all your efforts to help.

I have checked and resoldered any possible loose or dry joints including replacing most of the capacitors at the output stage as in the circuit you attached. The right channel cracking noise still persists.

I am prepared to replace the transistors if necessary. Which are the transistors do you think need replacement? I am not familiar with transistor and not sure the equivalent type since most of the existing transistor you indicated in red already obsolete.

Appreciate very much if you could help me to narrow down the parts that need replacement.

did u check your speaker ? is it still ok or burnded ?

 

[968driver]

Another thing that can be the cause of the strangest problems is glue.
Sometimes heavy components (elco's) are glued to the circuit board.
The glue also covers nearby resistors and diodes.
After some years, this glue turns dark brown and becomes conducting, and slowly eats away component wires.
Remove this glue!

Best regards, 968driver.

 

[Leeds]

I had replaced the following:

1. 2 nos of 2N5551
2. 2 nos of BD140

I used a pair of cheap speaker (ready to scrap) for the test. the woofer for one channel got damaged. The mid and tweeter still worked fine. The other channel was working fine without changing any transistor.

I soldered back the old transistors for the affected channel only to find that this time round, the fuse for that channel fused.

I could have installed the transistors the wrong way.

Is it possible for different manufacturers of transistor for the same 2N5551 having different pin out?

I am wondering should I purchased the transistors from the same brand and follow the pin out as per the data sheets?

Indeed, there were various brown spots on the joints and it is really challenging trying to nail down to the cause.

 

[Mooly]

The only time pin outs would be different is if the devices were fake. It doesn't matter that they are from different manufacturers.

Did you use a bulb tester as I mentioned earlier ? You don't connect any speakers until the amp is proved good by voltage tests

Brown spots around joints sounds like flux which isn't a problem.

Is the "good" channel still working OK ?

 

[Leeds]

The only time pin outs would be different is if the devices were fake. It doesn't matter that they are from different manufacturers.

Did you use a bulb tester as I mentioned earlier ? You don't connect any speakers until the amp is proved good by voltage tests

Brown spots around joints sounds like flux which isn't a problem.

Is the "good" channel still working OK ?

The good channel is still ok. I did not try using the bulb since the speakers on test were meant for scraped.

Should I replace the 2N5551, BD139 and BD140 on the faulty channel again ensuring the right pin-outs and of course this time round, test with a bulb.

Given the case now, I fear that the faulty channel now might have affected other components in the circuit.

 

[Mooly]

The bulb saves output devices and speakers from failure if things go wrong.

Its a very straightforward amp tbh. One approach that might work for you is to replace the transistors one at a time on the good channel (to prove the replacement devices you have are OK and that you are fitting them correctly).

Do you want to try that and work through it one at a time. But you mustn't connect speakers to the amp.