Cooling fan

[labb]

I have a build that the power tubes are running pretty hot and I want to add a cooling fan. Something I have never done before. Do I need to use a DC fan are can I use an AC fan and not have a noise problem. Thanks.

[jjasilli]

Have you searched the forum.  Lot's of older posts.  Note tubes are supposed to be very hot.  You probably don't need a fan.  AC fans move more air than needed and thus are noisy.  A 12VDC fan running of the 6VAC heater supply, rectified is about 9VDC.  This moves enough air and is very quiet.  Better not to blow air directly on the tubes.

[alerich]

I gutted a solid state practice amp and built a 50W JCM 800 clone inside it. All the tubes hang upside down (2xEL34 and 3x12AX7) and everything is really tight and close together in that small combo chassis. After about 5 minutes the chassis would get so hot you could not hold your finger on it for more than two seconds. That's too hot. I mounted a 12VDC computer fan in the bottom of the cabinet. The fan blows across the bottom of the cabinet and circulates air. I run it at 75% speed off of a 9VDC wall wart that I velcroed to the bottom of the cabinet. I wired an AC plug to the power switch so that the fan activates when the power switch is turned on. Works great and is pretty quiet. Might be too noisy for recording but it's a combo - you could just put the speaker cabinet in another room. For normal playing (particularly at the volume levels that I play at) it's a non issue.

jjasilli is correct that it is generally not a good idea to mount the fan so that it blows directly on the tubes but then again my old Boogie Mark II had a 120VAC fan (if I recall correctly) blowing right on the power tubes and I never had a problem with it.
 

[stratele52]

I have a build that the power tubes are running pretty hot and I want to add a cooling fan. Something I have never done before. Do I need to use a DC fan are can I use an AC fan and not have a noise problem. Thanks.

A picture of your amp will help to see if it need a fan . Tubes must be hot .

Tubes must be clean , no hand grease . Grease an dust keep the tubes warmer , not very good.

[labb]

Thanks alerich. That is pretty much my situation. I built a Bassman in a small chassis and the two 6L6's heat things up pretty good. I was thinking that if I could use a 120 vac fan that it would make things a lot simpler. I have a 12 vdc computer fan that I can use. I tried it with a 12 volt, 1 amp walwart and it actually ran at 13.8 volts. Was pretty fast and loud. Tried it at 6 volt off of a battery and it was very quiet. Haven't tried it at 9 volts. Think I will get a couple of 78xx voltage regulators and play with the speed a little and see where it falls. Don't think you have to move much air. Just some forced circulation.

[stratele52]

Fan running  faster are more noisy than those running a lower speed . Computer fan run too fast for the need of cooling an amp but are cheap and easy to find on any store .

A very slow fan will do the job with less noise. You just need a "small" but continuous air circulation.

Which one/ model we should buy  ?? 

[Jack1962]

I have used  both AC and DC fans in amps tube and solid state , if you use a AC fan all wires and the fan need to be a good distance from the amp circuitry( basically a pain in the rear) DC fans(brushless) are really your best choice , I like to use computer fans they work real well . Most of the time a cooling fan won't be able to cool off the tubes enough to be a problem , however if your in a warm room or a hot room a fan can be your amps best friend.