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I don't get any signal on the load, what am I missing? Shouldn't it amplify the input signal?

I have 50mA from the current mirror, the Vbe on Q10 and Q11 is around 0.75v

the differential amplifier

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    \$\begingroup\$ First rule of debugging: look at the intermediate points. Including the input. Figure out precisely where and how your expectation is not being met, then understand why. \$\endgroup\$ – Chris Stratton Dec 15 '18 at 15:59
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As Chris says in comments, you should be able to solve this yourself by probing different nodes and seeing where their behavior is not what you expect.

In particular, check if all the transistors are biased into the correct mode of operation.

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  • \$\begingroup\$ Sure, but there's a reason that comment was posted as a comment and not as an answer - and that is that it is a suggestion for how to find a solution, not itself a solution which is what the answer field is reserved for. You've been here long enough to know that. \$\endgroup\$ – Chris Stratton Dec 15 '18 at 16:53
  • \$\begingroup\$ @ChrisStratton, go tell it to the guy who actually gave the solution. \$\endgroup\$ – The Photon Dec 15 '18 at 16:54
  • \$\begingroup\$ Unless you want to argue that the question should be disallowed (I don't see your close vote, or anyone's) then stating the solution is precisely what the answer form is reserved for. \$\endgroup\$ – Chris Stratton Dec 15 '18 at 16:55
  • \$\begingroup\$ @ChrisStratton, giving a clue to the solution for homework-like questions, or answering a different question (for example, for X-Y problems) is entirely common and accepted here. \$\endgroup\$ – The Photon Dec 15 '18 at 16:56
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The capacitors C12 & C13 are blocking the base currents. Add a 10K resistor from each input transistor's (Q10 & Q11) base to ground to allow a DC return path to ground.

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