@MathematicalOrchid I think correct heat dissipation requires some gaps between the "boxes" so its not just to get to them ... but yes that photo is mostly empty ... Would be interesting to know the temperatures ... In one of mine previous jobs we had a small Internet backbone hub in a basement and that beast was at 48C (degrees Celsia) with open windows and -6C outdoor temperature and cooling fans spinning laudlly... and that was around 2003 now imagine old TTL or even tubes ... – Spektre Jan 25 '19 at 9:43