Hook Up Wire for Pre and Power Amps

It depends on what the wire is conducting. Line level signals are usually very low current so you can go for a high gauge wire... 20AWG+. Silver plate is nicer to solder but tinned copper will be fine as well. Power carrying wires will need to be rated for the current but the runs are short so you are fairly safe... just check they don't heat up on full load.
The most important thing is that you protect the signal wire from the RF interference of the power circuit. This can be done either by tightly twisting all wiring in the chassis or using shielded conductors for the power wires.

Thanks for your recommendations!  I have learned that solid core wire might have an advantage over stranded.  The 845 tubes I have in my amps draw as much as 1000VDC so will require a lower gauge for sure.  Correct?

The 845 tubes I have in my amps draw as much as 1000VDC so will require a lower gauge for sure. Correct?

Nope.  Gauge is on amps.  Insulation is on voltage.

So make sure the gauge is the right size for the current (A), but the insulation on that wiring has to withstand the V differential present, regardless of the current.

Best,

E

To clarify: 

The insulation needs to be greater than the voltage DIFFERENCE, not just the voltage.

For example, if the insulation comes near -200V and carries +1000V, then the insulation must be rated at least 1,200 V.