..I built two of these PCB ax 14, both have the same problem, BIAS did not come to a standstill at zero !! I verified the operation P1 is ok, BD139 is on heat sink with insulation, the welds seem ok .... the PCB is very simple ... the margins of error are low .... I have not yet found the problem
... I made measurements on this pcb, ... near the R16 I measure 0Volt .... All this because the BD139 is not placed on the heatsink of the transistors? strange
They are only passing 1V so they are fine. That -54V is measured to ground. C-E is only 1V.
Everything looks right up to q8 and q9. Make sure they are not faulty and check the pins are correct per the data sheet.
The base of Q11/Q13 should have around 1.1v (+&-).
Where did you buy the transistors from?
... I made measurements on this pcb, ... near the R16 I measure 0Volt .... All this because the BD139 is not placed on the heatsink of the transistors? strange
It looks as though you have a short to ground on the collectors of Q8 and Q9. Have you checked them for that?
OK, quick check in to make sure I am on track.
AX14, first channel hooked up and measured. All .33ohm resistors measuring 10-11mv as is the output. All settled down once the heatsink warmed up, sitting on a steady 36C, its a fairly substantial heatsink (as per pic).
So does this all seem to be within spec?
Thanks.
Edit, after 15-20 mins the heatsink has cooled to 33c.
AX14, first channel hooked up and measured. All .33ohm resistors measuring 10-11mv as is the output. All settled down once the heatsink warmed up, sitting on a steady 36C, its a fairly substantial heatsink (as per pic).
So does this all seem to be within spec?
Thanks.
Edit, after 15-20 mins the heatsink has cooled to 33c.
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Thanks Prasi.
R23 is soldered under the board bypassing C13 so both options there.
The heatsink its mounted on is part of the case which I got from Aliexpress. Will post some pics once its all together.
And thanks for the board design etc. and help during my build. The boards are great to work with, very clearly labeled and all components fit well. Nice straightforward build.