Any opinions on Cooling fans for Tube Amps?
- Thread starter pantoramasan
- Start date
triode17
Super Member
Let me open up a bigger question, why is everyone so concerned about power transformer heat? They naturally run hot. Just because you can't keep your hand on it for more than a couple of seconds, does not mean it's overheating. I just looked up specs. of magnet wire and found that in general, the wire must withstand a minimum of 155 deg.C. or 311 deg. F. That's damn hot!
Having designed and built a few tube amps now, if the transformer is overspec'd (larger than needed), it will run relatively cool, but the cost is high.
For commercial applications, like Dynaco ST70, yes the tranny runs quite hot, about 75 deg.C. (167 deg.F.) on the laminations but that was a cost cutting measure to keep a price that an average person could afford. So, I wouldn't worry about the heat in a commercial product but in a custom designed amp, it can become a concern.
Having designed and built a few tube amps now, if the transformer is overspec'd (larger than needed), it will run relatively cool, but the cost is high.
For commercial applications, like Dynaco ST70, yes the tranny runs quite hot, about 75 deg.C. (167 deg.F.) on the laminations but that was a cost cutting measure to keep a price that an average person could afford. So, I wouldn't worry about the heat in a commercial product but in a custom designed amp, it can become a concern.
triode17
Super Member
sKiZo - A few comments about your Dyna clone. First off, nice work. But I see a potential trouble spot, the distance between the KT120 pairs. According to the Bible (aka the RCA, RC-30 tube manual), power tubes should be spaced at least 1.5 tube diameters away from each other. If not, they tend to heat each other. This causes the plates to get hotter than normal, which in turn can cause the plates to emit gases trapped inside them. In turn, this can cause the ('silver') getter flashes to wear out faster, thus shortening the expected tube life. Your passive cooling design may not be enough and short of making a new top panel, I would test the air circulation by placing a lit cigarette or incense-stick under the unit by the inlet vents.
If the circulation seems too slow, then add a 4" fan, running at half voltage, blowing into the bottom or side of the cabinet should give a nice, cool flow.
One more thing, the P.Trans. temp may not have reached equilibrium in just an hour. Mine seems to take about two hours. Also, measure the hot spot, which is the laminations, not the end bell cover.
If the circulation seems too slow, then add a 4" fan, running at half voltage, blowing into the bottom or side of the cabinet should give a nice, cool flow.
One more thing, the P.Trans. temp may not have reached equilibrium in just an hour. Mine seems to take about two hours. Also, measure the hot spot, which is the laminations, not the end bell cover.
