[Amps] Holes vs. screen for chassis ventilation?

[John Lyles]

For high power HF and VHF amplifiers where I need to pass air through a hole, I have been using copper hardware cloth, sold by McMaster Carr, instead of aluminum screening. 
It is made from heavy copper wire, and I use a resistance soldering (hot lips we call them) device to solder all the way around the circle or square, to prevent unraveling
of the mesh when it is handled. The solder is applied to crossing wires, a little spot at every crossing. For VHF I am using same stuff with smaller holes, but still allowing 
good airflow, and also putting a long tube (5 inches) to act as additional suppression. The screen wires need to be placed in direction of wall current flow in a cavity circuit, if 
used there. If at the top above the anode, beyond the short circuit (in a quarter wave tuned circuit) then this doesn't matter. I soldered the entire mesh into a copper ring, 
using a hot plate, and had the entire assembly silver plated (it looked rather crude after soldering).  It now looks very professional and has low resistance to RF current. 

This is in the two air ports for the 3 megawatt 200 MHz cavity amplifier that I am about to energize the first time either this week or next. 

73
John 
K5PRO