HI,
I'm really trying to keep all question here on the group and not in private email.
I was trying to bring linear PA back to life ¨C as I see, the problem is that I have +12V on gates of BS170
in TX after the bias schema and I can`t find a reason of it. Seems that everything in this part is working,
BIAS+ signal is ok (5V),Q205 is switching, Q202 is also switching, for Q201 ¨C I don`t know as it is getting
+0.4V on TX after Q202. Just in case I ??replaced Q202 and Q201 ¨C no effect. +12 V on TX ¨C as I see it
overloads the Q203/Q204 pair and it doesn`t work at all.
So, the questions that could help me:
1.??
Having 12V on the gates tells me you have miswired something, inserted it backward
or plugged a part into the wrong holes.? Also with 12V on the gates if the source
resistors are not burnt out that would be a surprise either that or you have destroyed
the BS170s.? FYI 12V applied to the gates basically turn the mosfets full on (saturated)
and the operating current for that stage should be quite high (greater than 1A) which
would be destructive.
>>>What is the proper bias voltage on Q203/Q204 ¨C as I remember from SoftRock similar schema, it should be about 2.5V, right?
2.?????? Is 0V on RX and +0.4V on TX on base of Q201 correct?
3.????
Those sounds reasonable. Its the same circuit.??
>>>Maybe you do have a bias circuits schema with proper voltages on RX and TX? Or maybe you remember anybody posted it in the group?
No I do not, best I remember its not been asked before.
Allison
