Large resistor between anodes

In a few pre schematics I've seen a large R connecting the anodes of the two stages (directly, after load Rs). For example an earlier V72 has 4M, but missing from the earlier V41.  A later version omits it again.  REDD47 has a 2M.

Is it some sort of reference for the 2 plate DC, or some sort of feedback leaking a bit of music from stage 1 directly to output?

It is often intended as negative feedback. Think of it as an op amp. The anode of the second tube is the output, the grid of the second tube is the -ve input and the resistor between the anodes is effectively the feedback resistor between the output and -ve input. (Think of the cathode of the second tube as the +ve input which in this instance is grounded).

Add a resistor in series with the -ve input and you have a regular inverting input - but hang on, there is no input resistor!. This is what confuses most people. In fact there is an input resistor - it is the output impedance of the first stage which is the anode resistor in parallel with the the internal anode resistance of the tube.

Cheers

Ian