PreAmp Biasing Trimpot issue?

[lesabb]

I am newbie and trying to build the pre-amp section of the Neve 1073. I decided to bread board the BA283AM ONLY as per the attached schematics. I think there is a problem but i can’t seem to find it. The collector voltage on the 2N6248 is 20.6V. Shouldn't it be higher? When I turn the trimpot nothing happens. The Base voltage is ~10.6V and the E is at ~ 10V, which I think is OK but a bit higher than previously reported (~3V). Consequently, the C voltage of Q1 is at ~10.6V (much higher than the reported 3.6V). The transformer is connected to the 24V PSU and to the output of the BA283AM as per the schematics.Any troubleshooting ideas? Thanks

Luc

[Seekonk]

I don't see any bias turning Q1 on.

[lesabb]

THis is what the whole thing is like.

[Seekonk]

Obviously the output transistor it being turned on much, so the issue is in Q2&3. These should follow .6V drops.  When you get enough voltage 47 ohm, Q1 will stabilize the circuit.

[lesabb]

I don't know if I understand but the Q1 & Q2 Vbe is 0.6V drop

[Seekonk]

Q2&3 are a simple darlington.  Problem should be obvious from the voltages.

[Andy Watson]

The Base voltage is ~10.6V and the E is at ~ 10V,

Either the emitter resistor is not 1k2, or the collector resistor is not 68k - or possibly Q2 is dead or wrongly connected. 10V across 1k2 would require a current of 8.3 mA - so either the collector circuit of Q1 is wrong - too low resistance, or the emitter circuit has too much resistance.

[lesabb]

Thanks, I forgot that I was using MPSA06, not BC184C! Pinout is the opposite! HOWEVER now when i power up, the 47R smokes! I will go back and re-wire. My 47R is a 2W resistor.