OT - installing fans in an amp head

[ESPm2M]

I want to install two large computer case type fans in to my amp head but I am concerned about the fans creating noise in the signal.  Is this going to be an issue or are these fans so low voltage and possessing a minimal magnetic field that its not an issue at all?

Do they make fully shielded comp. case fans? I'll google it...

[b_rogers]

i think i remember someone saying to steal the power from the filament heaters and starve the fan.  so if its a 12v fan, run it at 6 volts..less noise

but i may be wrong...


Brent

[Alex C]

Here's a page by Paul Marrossy about how he added a fan to his Blues DeVille.  He used a separate 12V transformer though.

http://diyguitarist.com/GuitarAmps/Bluesdev.htm

Alex

[Peter Snowberg]

Keep in mind that the filaments may be running on 6 volts AC.

Run the 6VAC into a bridge rectifier and past a big cap like 2,200uF. You'll end up with something like 7.5 to 8 volts DC.... perfect for running a 12V brushless fan at lower noise levels.

Just make sure the fan is away from the first stage of the preamp and the reverb tank and you should be fine.

[ESPm2M]

Here's a page by Paul Marrossy about how he added a fan to his Blues DeVille.  He used a separate 12V transformer though.

http://diyguitarist.com/GuitarAmps/Bluesdev.htm

Alex

thanks for the link! I will definitely read through it.

[ESPm2M]

Run the 6VAC into a bridge rectifier and past a big cap like 2,200uF. You'll end up with something like 7.5 to 8 volts DC.... perfect for running a 12V brushless fan at lower noise levels.

Just make sure the fan is away from the first stage of the preamp and the reverb tank and you should be fine.

Thanks for the info!

I plan on installing two fans (one at each end of the head).  It doesn't have reverb, but will having a fan on the preamp/power section side (as opposed to the transformer and rectifier side) cause problems? BTW, I am referring to a Mesa Boogie Triple Rectifier head which I would cut a square into each side of the the head cabinet to mount the fans.

[Peter Snowberg]

The only way to measure what you'll get is to make a temporary installation. Move the fans around by hand and see what happens. Every fan make/model is different, as is every amp.

[petemoore]

I'm running mine at 117Vac, right off the line in switch, and noise isn't a problem...YMMV

[Aharon]

I want to install two large computer case type fans in to my amp head but I am concerned about the fans creating noise in the signal.  Is this going to be an issue or are these fans so low voltage and possessing a minimal magnetic field that its not an issue at all?

Do they make fully shielded comp. case fans? I'll google it...

Why do you feel you need TWO large fans in your amp?.
Is it overheating?.
The best way to try is to get a brushless 12VDC fan and run it at 6VDC with a wallwart.You can use a bracket,velcro or whatever to hold it and that way you don't hack into your amp.That may be all you need to keep the amp cool.
Aharon

[Paul Marossy]

I have used a wall wart to power the fan in two of my commercially manufactured amps. The three amps that I have built have fans that are powered by a well filtered silicon diode full wave rectifier off of the heater supply. I control the fan speed with a pot wired as a variable resistor. The idea is to move as much air as possible without it being too noisy. I also included switches on the fan power supplies to allow for quiet recordings.

The only thing to keep in mind is the current draw of the fan. Adding that to an already taxed power transformer can push it over the edge...

[ESPm2M]

I want to install two large computer case type fans in to my amp head but I am concerned about the fans creating noise in the signal.  Is this going to be an issue or are these fans so low voltage and possessing a minimal magnetic field that its not an issue at all?

Do they make fully shielded comp. case fans? I'll google it...

Why do you feel you need TWO large fans in your amp?.
Is it overheating?.
Aharon

Aharon, what can I say? Its another project that will be fun for me, will result in increased tube life, and just plain look cool in the end.  :lol:
The head is not overheating, btw.

[GreenEye]

Preface:  I love tubes, use 'em, and don't know much about 'em. :?

Not to knock the fan thing, but do fans really prolong an amp's tubes?  And if the tubes are getting cooled, wouldn't that affect the tone in a negative way, given that they probably sound better warm or hot than "cool."  I could see cooling a 7868, since those are so rare and expensive, but with an EL84 or something - shoot, let 'em burn, they're cheap.

[Paul Marossy]

A fan inside your amp will not lower the operating temperature inside of the tube that much, if at all. Therefore, it shouldn't really affect the tone, either. But, blowing air across the glass envelope does help the tube to dissipate the heat produced a little more efficiently.

Tubes cheap? I don't consider $150 to re-tube a Twin Reverb to be cheap...

[Aharon]

Aharon, what can I say? Its another project that will be fun for me, will result in increased tube life, and just plain look cool in the end.  
The head is not overheating, btw.
ESPm2M

Just curious that's all.Have fun.
Aharon

[ESPm2M]

Preface:  I love tubes, use 'em, and don't know much about 'em. :?

Not to knock the fan thing, but do fans really prolong an amp's tubes?  And if the tubes are getting cooled, wouldn't that affect the tone in a negative way, given that they probably sound better warm or hot than "cool."  I could see cooling a 7868, since those are so rare and expensive, but with an EL84 or something - shoot, let 'em burn, they're cheap.

Honestly, and incase you didn't pick up on it, its really about the fun/cool factor and it would be very much in the spirit of DIY.  

To attempt an answer to your question about tube cooling - When people refer to tubes sounding better "hot" it really means biased "hot" (biased with a higher plate voltage than is typical of that tube). Most manufacturers tend to bias their amps on the "cold" side especially in the case of preset bias amps.  Physically cooling the tubes increases the life of the tube filament, with no affect on tone.  Can someone check me on this?

[ESPm2M]

... what Paul said.

[GreenEye]

I'm all for DIY.  It'll look cool too.  I've got a Line 6 Flextone I head (I know, it might have well been made by Satan), and it's got two huge fans on it that'll kick on if it gets too hot.  The newer ones don't have fans I don't think.

[ESPm2M]

So I found some interesting parts that might suit this project...

Paul, or anyone else, do you think that the NTC Thermistor (found at the link below) can be used in a circuit to automatically control fan speed in place of the pot you used in your mod?

http://www.bgmicro.com/lmad.asp

Also, any comments on the Panaflo FBA12G12M 120mm 12v fans that are also there? I think they would be perfect!

thanks

[guitarhacknoise]

What about dust?

[ESPm2M]

What about dust?

A very good point, that I have considered. It shouldn't be a problem at all. First, the head is wide open in the back to begin with and it has a large grill vent on the top, so dust can easily get in as it is.  The solution to this is the cover supplied by Mesa-Boogie, that I put on it when ever it's not in use. As for the fan mod, I plan on putting some sort of thin fine mess over each fan on the inside to reduce excessive dust and dirt while in use.