OT - Fan in Solid State Combo

[nicksmurf111]

I have a Yamaha G50-112III.  It has a jiant aluminum heat sink behind the speaker.  I believe the amo is rated 50 watts into 8 ohms, and I usually push a 4 ohm load without trouble (probably putting around 70 watts into it at least).  I was checking how hot the heatsink was just now after playing at full volume for a half hour.  It's hot enough to scold me If I grab it hard.

Is this bad for the transistors?  Should I stick a fan at one end of it?  I could wire up a computer power supply type fan.  Could I wire it right to the amp power supply without inducing hum into it?  Or should I wire up a seperate tiny transformer, bridge, filter caps for the fan?

I know a lot of tube and solid state amps with the components tucked inside have fans, but I have a jiant heat sink sitting there.  The only problem is it seems to be getting so hot I'm worried about my transistors frying.  (I'm not biasing the amp, I've blown to many bias circuts on other amps with dirty trim pots).

[Peter Snowberg]

Sure, you can just get a DC brushless fan and point it to the heat sink. If you are driving more than the rated load, you might also want to think about adding some more surface area to the sink by bolting on an additional sink and using heat sink grease between the junction.

You probably will not get noise from the fan, but I would locate it as far from the preamp as you can.

Thanks to all the CPU fans these days, you can now get cheap units with thermosatic speed control. That helps to reduce ambient noise when it isn't needed.

Most power transistors are built to be able to run hot enough to burn you without problems, but the life of the parts and the solder connections between them are reduced.

Take care,
-Peter

[nicksmurf111]

The amp is rated to drive a 4 ohm load.  I was just worried that it if I played it really loud for really long that it might fry a transistor.  I donno if it's worth the fan or not, extra noise...

[Nasse]

I dunno nothing about your Yamaha amp but because yammy is wellknown and respected thing in a bisnes it should do without additional cooling. And maybe the circuit has some thermal protecting, who knows. But if you play with a loud band in big venue so 50 watts solid state may have some hard work to do. If I were you I would put a switchable fan so you can switch it off when the noise disturbs.

I have this high fan noise all the time, my computer has some extra cooling and not the quietest one. I am trying to listen soundfiles from smallish mutimedia speakers :mrgreen:

[brett]

If you do put in a fan, you might want to try running a computer fan at under the rated voltage.  For example, a 12 volt fan run with 6V is a lot quieter, but still pushes lots of air.  If you have a thermometer, you could check that your trannies are running at uner 150C (about 300F).  I believe that even rugged trannies (like 2N3055s) running case temperatures above 150C might be getting close to their limits.