Apex AX 20 amplifier problem....

abys

Member
2016-05-07 11:36 am
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....
 

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abys

Member
2016-05-07 11:36 am
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....
 

abys

Member
2016-05-07 11:36 am
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....
 
Not exactly. The source is "caput" - latin.
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.