Vent holes for heat. What size diameter?

Hello,

I'm curious about what size and how many holes one can drill in a case and still maintain the same shielding the case provides?

I have a dual LA2A with 8 tubes and some sand resistors on the AC heaters, all of which build up a bit of heat. Been thinking of drilling some vent holes above the tubes but don't want to compromise the shielding of the case.

I think they would have to be quite small. The holes would have to be much smaller than the wavelength of the frequencies you want to keep out. So bigger holes means higher frequencies get it. I think mobile phones are in the 1Ghz range which has a wavelength of less than 1 foot so 1/100 of that would be ~1/8" hole. But I could be talking out of my petard.

Safety agencies have rules about the size of holes they allow to prevent human fingers touching hot or energized inner goodies.

They use a probe that IIRC was 1/4" or less to confirm.

JR

JW said:

Hello,

I'm curious about what size and how many holes one can drill in a case and still maintain the same shielding the case provides?

I have a dual LA2A with 8 tubes and some sand resistors on the AC heaters, all of which build up a bit of heat. Been thinking of drilling some vent holes above the tubes but don't want to compromise the shielding of the case.

Click to expand...

Any holes will decrease shielding to a degree.
Question is to what degree and what is acceptable.
Need to consider what frequencies / range of frequencies is of concern ?
Basically smaller holes maintain shielding effectiveness to a higher frequency.
Also the material depth (in this case the thickness of the enclosure) is a factor - the thicker the panel the better the shielding.

Where to start ? 3mm diameter holes (or 1/8" if working Imperial) is typical ime.