No top on mine at the moment either. I built an Oak piece for it to sit in, and I incorporated an 80mm computer fan in the top blowing down on it. After playing for over an hour, the heat sinks were cool to the touch. So that was a good thing to find out. Now, if it should have some heat build up to work properly, I might need to reduce the speed of the fan. I didn't hear anything that would make me think it changed the sound though. Have any thoughts?
I'm anxious to get the 2 RCA clear tops I ordered Sat. night to see if they will rival the Balwin/Raytheon long black plate that I have settled on as my best tube so far. Then I think I'll see about doing some of the mods. Jim.
Well, if you're using a computer fan, likely it's running on a DC power supply. That ought to produce less noise, if any. I use a Thermaltake USB fan, and I do not hear any RFI noise as a result of placing the unit behind my amp. (I don't remove the top of my stock amp for cooling purposes - the fan blowing from the rear is sufficient).