Hi...this is regarding the apex amplifier AX20... When I first tested the amplifier using series load lamp I forgot to connect the two sides of the emitters of 2sc5200 and 2sa1943 together using the wire jumper....it resulted in burning of a 100 ohm emitter resistor of 2SA1837.
Now, after I connected the jumpers together, the 2SA1943 transistor sect ion is consuming around 2.5 amperes...what does it indicate ???? They are getting warm but the other transistors are OK....the lamp gliws brightly..... I am using a + - 35 volt dual power supply
Does it and indicate a short in the 2SA1943 transistors...???? All of them are getting hot....but not extremely hot. I suspect problem in drivers too....
Please advise....
Now, after I connected the jumpers together, the 2SA1943 transistor sect ion is consuming around 2.5 amperes...what does it indicate ???? They are getting warm but the other transistors are OK....the lamp gliws brightly..... I am using a + - 35 volt dual power supply
Does it and indicate a short in the 2SA1943 transistors...???? All of them are getting hot....but not extremely hot. I suspect problem in drivers too....
Please advise....
Attachments
Measure the voltage from base to emitter on EACH 2SA1943.
It should be around 0.6V or less.
You will likely find at least one of them which is much lower, say around 0.2V or less, and this one is kaput.
Hugh
It should be around 0.6V or less.
You will likely find at least one of them which is much lower, say around 0.2V or less, and this one is kaput.
Hugh
Hugh, if you mean the German phrase for "broken": "kaputt" is written with 2 "t".
Best regards - Rudi_Ratlos
Best regards - Rudi_Ratlos
I checked the output transistors..all of them are receiving .6 volt bias.... But the BD139 is receiving only 0.2 -0.3 volt bias only.....the 2SC5200 transistors are having zero bias voltage.....they are not heating up .......
Another interesting fact is that the pot which controlled the biasing voltage of the BD139, is varying only up to around 600 ohms, thus putting the BD139 at a maximum bias of .3 volts only....
Another interesting fact is that the pot which controlled the biasing voltage of the BD139, is varying only up to around 600 ohms, thus putting the BD139 at a maximum bias of .3 volts only....
Here are my findings :
2SA1943 seems to be biased at 0.6 volts....but 2SC5200s are at zero bias
BD139 is biased at 0.2 volt only....the pot which controlled its bias, didn't moved after a value of 600 ....ohms....I will try a new trimpot....
2SA1943 seems to be biased at 0.6 volts....but 2SC5200s are at zero bias
BD139 is biased at 0.2 volt only....the pot which controlled its bias, didn't moved after a value of 600 ....ohms....I will try a new trimpot....
Hi Rudi,
I had a look as I've not seen it with two T's. Interesting story. It went from the french word Capot to the German Kaputt to the English Kaput.
Can you measure voltage across emitter and collector of BD139 with reference to ground.
I measured it... The voltage across base and emitter is .38 during that time....
Voltage at collector w.r.t. ground: 1.34 volts
Voltage at emitter w.r.t. ground: 2.05 volts
Voltage at collector w.r.t. ground: 1.34 volts
Voltage at emitter w.r.t. ground: 2.05 volts
Though I didn't care much, the 3 LEDs were also not glowing....leaving the other two leds, shouldn't the power led turn on ????
I used bc547 instead of bc550 as in the pcb.....I hope it won't contribute to my problem....
I used bc547 instead of bc550 as in the pcb.....I hope it won't contribute to my problem....
Remove the load, then set the offset <10mV with respect to ground.
I suspect that the offset is high, we have two fundamental parameters on amplifiers: quiescent current and offset voltage.
Interesting that kaput is not accepted in my word checker! Thank you for your input, Rudi, nice to hear from you!
Hugh
I suspect that the offset is high, we have two fundamental parameters on amplifiers: quiescent current and offset voltage.
Interesting that kaput is not accepted in my word checker! Thank you for your input, Rudi, nice to hear from you!
Hugh
Sorry guys, I know this is OT but:
https://en.wikipedia.org/wiki/Caput
and Kaput:
Kaput originated with a card game called piquet that has been popular in France for centuries. French players originally used the term "capot" to describe both big winners and big losers. To win all twelve tricks in a hand was called "faire capot" ("to make capot"), but to lose them all was known as "être capot" ("to be capot"). German speakers adopted "capot," but respelled it "kaputt," and used it only for losers. When English speakers borrowed the word from German, they started using "kaput" for things that were broken, useless, or destroyed.
I will stop now.
Hi,
I did the tests without any load...the dc offset seems to be fixed at around 100mV. The pot was examined...it works properly.......I tried varying the pot...but it does not respond to that too....
I did the tests without any load...the dc offset seems to be fixed at around 100mV. The pot was examined...it works properly.......I tried varying the pot...but it does not respond to that too....
Hi,
To adjust the offset you must replace the 1K rezistor that connect's C - B of the BD139 with 1.5K, The same problem I had with AX14, i think it's the same problem.
Best of luck!
To adjust the offset you must replace the 1K rezistor that connect's C - B of the BD139 with 1.5K, The same problem I had with AX14, i think it's the same problem.
Best of luck!
You can do another thing, verify pcb with the schematic, in particular the
transistors pin B C E...........
transistors pin B C E...........