PNP differential pair in ltspice

[vixo]

I am trying to understand this circuit (below) as I'm trying to fix a piece of equipment. I tried to simulate it but the simulation (ltspice) is giving me strange results. I would have expected to get a high gain circuit, as the top resistor is 470 and the bottom is 30K. If I look on R5 to ground I get a signal which is only a few micro-volts around 15V.

I'm not sure if I need to be driving this circuit differently. I haven't simulated the whole thing because the schematic is quite big. I included a second picture that shows more of the circuit (this doesn't work either, so I tried to start with a smaller chunk and work upwards) but I would rather not simulate more of it.

Can anyone help me understand what I should do to see the normal circuit behaviour? I also included the ltspice file

any help much appreciated!

[mikerj]

In the simplified top diagram the constant current source Q3 is not biased into conduction, which in turn means Q1 and Q2 are also not being biased into conduction.  The lower diagram has additional components R3,R4 and V6 to bias Q3, but from inspection it looks like this would be turning on Q3 far too hard and likely saturating Q1 and Q2.  However the node "VM" may play a role in this and I don't see any other matching net names.

[vixo]

ahhh, thankyou so much. I biased it correctly and everything works as expected