Bryston 4B SST clone

[Fetamp]

Unfortunately what happened mad:

 

[amplidude]

Auchh, what happend?.
Until you're sure the amp behaves as it should, leave the ballast on rails, bulbs resistors etc.
Did it oscillate?

 

[chalky]

Bummer!! Two questions. What were you doing when it happened and what insulators do you have under the output transistors ( cant see any )?

 

[chalky]

Actually more questions. Do you carefully check the drill holes for burrs before you mount transistors on the heatsink, and do you check that the collectors are not shorted to the heatsink after you've mounted them?

 

[Fetamp]

Bummer!! Two questions. What were you doing when it happened and what insulators do you have under the output transistors ( cant see any )?

Hi.....AMP worked perfectly other than little low gain,I checked bias voltage of Q24 and suddenly fired and burned all components in + rail up to Q13,please give suggestions for causes?

 

[Fetamp]

Actually more questions. Do you carefully check the drill holes for burrs before you mount transistors on the heatsink, and do you check that the collectors are not shorted to the heatsink after you've mounted them?

All were in correct order......

 

[Fetamp]

Hi..Chalky Amplidude ....please let me know is it ok to replace 49.9r (R38-41) with 47r or56r ?
Thanks

 

[amplidude]

Well, I think you accidentally shorted something while measuring bias, as to the 49.9r a 47 should work its within 6%, maybe chalky knows more, but I wouldn't hesitate.

 

[chalky]

I think amplitude is probably right as to the likely cause of your burnout. I used 51R with no problem in my amps. I'd replace all four 49.9R resistors with 51R types - the absolute value isn't too critical but its important that all four values match as closely as possible ( or reasonable! ).

 

[amplidude]

When I measure in tight places with high voltage / current I put tape around probe so only the tip is free, recently bought hirschmann clip probes, they are worth every penny, also their needle probes.

 

[chalky]

Don't forget to check all of the other output and driver transistors when you're replacing the burnt out devices. Check Q5-Q8 as well

 

[Fetamp]

Thanks both of you Chalky and Amplidude for your valuable inputs...if anyone can please post a picture of Original MJL21194/93.Please have a look my one and comment.
Thanks

 

[amplidude]

Are you worried it's fake?
My first impression is it looks like the real thing, I found a thread that deals with fake mjl21193/94 with pics.
One could measure them and see if they match spec sheet data.
https://www.google.com/url?sa=t&sou...Vaw2GGC3uD7jVDZuOxfR6HHm8&cshid=1579845761292

 

[chalky]

Looks like mine too. Marking says made in Singapore in 2017 work week 12. Who did you buy them from?

 

[Fetamp]

Looks like mine too. Marking says made in Singapore in 2017 work week 12. Who did you buy them from?

Hi...thanks for your reply I’m a Sri Lankan..which is a small beautiful island like a paradise situated in Indian Ocean .I bought them form Colombo ...the capital city of the island.And I’m a medical doctor with little knowledge in electronics but suffering with fever.Oh ...that is myself....really ? it’s look like original ? but I saw some discussion in forum that original one is rectangular and no projections at base of pins ?.

 

[chalky]

I was really trying to establish if you'd bought them from a reputable distributor rather than somewhere like ebay. What makes you think your parts may be fake?

 

[amplidude]

I'm sure the amp didn't blow up because fake mosfets or not, but now that you have some burned mosfets you can open one, apparently the die on fakes are smaller, the are pics on diyaudio of genuine verses fake die.

 

[chalky]

Yeh put it face up in a vice and squeeze - that usually cracks it open and leaves the die intact.

 

[Fetamp]

Reborn.....

 

[amplidude]

Very good.
Did you change many parts? And have you tried a power up.
Mistakes happen, I mixed up a P and N channel mosfet today, luckily I had fail safe resistors on.