[Amps] coax length between transceiver and amplifier

[STEPHEN L SALA]

I was wondering how long you can run coax between a modern transceiver and the amplifier?  And I have two cases:
 
1  HF
2  6 meters
 
Since my ham desk is in the middle of the room so I can have access to all sides of the U-shaped desk for wiring, and the desk is holding about all the weight it can support, it would be advantageous to put the amplifiers on a separate desk.  This would require  40 feet of coax in the internal run between the units for each.  
73
Stephen L. Sala (Steve) K7AWB Nine Mile Falls, WA DN17es