Hi folks,
I am struggling with an amplifier I have replace the output transistors in.
The service manual states that it is critical to set the quiescent current when any components have been replaced. Just incase I turn the unit on normally and they all blew again, I used the lightbulb trick and all was (seemed) fine.
The light bulb lit and then dimmed immediately. I also put a known good unit onto the light bulb and it behaved the exact same way - so I deduced that all was well.
When checking the quiescent current I had an imbalance. They say you should set in to measure 6.6 to 8.8mV across R's 4, 14, 44, 45.
One side read "zero" across the resistors ... the other read -76mV. I could not set them and assumed it was because of the lightbulb.
So I removed the lightbulb - after all, it didn't "light" brightly and behaved in the same way as the known good unit... I got sparks (from R42) and blew the output transistors again...!
My question is - should I be able to set the quiescent current whilst using the lightbulb trick...? I know voltages would be lower overall but should I be able to get an idea is setting the quiescent current will work...?
Appreciate any help,
Cheers,
Tom
I am struggling with an amplifier I have replace the output transistors in.
The service manual states that it is critical to set the quiescent current when any components have been replaced. Just incase I turn the unit on normally and they all blew again, I used the lightbulb trick and all was (seemed) fine.
The light bulb lit and then dimmed immediately. I also put a known good unit onto the light bulb and it behaved the exact same way - so I deduced that all was well.
When checking the quiescent current I had an imbalance. They say you should set in to measure 6.6 to 8.8mV across R's 4, 14, 44, 45.
One side read "zero" across the resistors ... the other read -76mV. I could not set them and assumed it was because of the lightbulb.
So I removed the lightbulb - after all, it didn't "light" brightly and behaved in the same way as the known good unit... I got sparks (from R42) and blew the output transistors again...!
My question is - should I be able to set the quiescent current whilst using the lightbulb trick...? I know voltages would be lower overall but should I be able to get an idea is setting the quiescent current will work...?
Appreciate any help,
Cheers,
Tom