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Lookig for 12v....?


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5/22/2000 3:14 PM
Casey4s
Lookig for 12v....?
Hi,  
 
I am in the process of building an Ampeg SB-12 clone/variation. It started life as a 2x6L6 amp, then to get a little more headroom I went to 2x7027A, but now I decided to use a pair of GE NOS 6550s. The problem is that the cabinet (head) is already completed (ID=15"x8"x8") and the chassis is 13"x7"x2". With the 6L6s or even the Tung-Sol 7027s there was adequate room for VENTILATION! But with the taller fatter bottles of the 6550s with increased heat from twice the heater current, then add in 2x12AX7s and a GZ34, it seems like a lot of heat. I do have room for a small computer fan that would really make a difference in heat dissipation.  
 
Where do I find a power source for the fan without toasting the fan? I initially thought I would simply hook it up to the filiment supply, but something says too much "current"!!! and I don't want to get a "wall wart" in the act. Does anyone have any suggestions? Is there a better way to get a fan in there? Obviously I don't want a noise problem from either the fan itself, or from the fan reaking havvoc with the circuit.  
 
Suggestions appreciated...  
 
Casey4s
 
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5/22/2000 3:25 PM
anonymous
casey,  
 
how much room do you have underneath the chassis? your best bet is to go to radio shack or some such place, and pick up a small tranny. then rig up a completely separate supply, tying it only to the line switch on the primary of your original PT.  
 
as you said, if you're stressing out the filament winding already, don't make matters worse with a fan. the separate supply gets around that problem.  
 
hell, you might even use it for some DC filaments, maybe for the input stage?  
 
ken
 
5/22/2000 8:06 PM
Reid Kneeland

Why not just use a 115V fan? Or a 230 run at 115, which will be very quiet (mechanically, that is... electrically is harder to predict).  
 
Reid
 
5/22/2000 9:32 PM
Stephen Conner

Reid has a good point... an AC fan would save you a transformer. I have heard of 230 volt fans run at 115V, but some AC fans are amazingly quiet even at the proper voltage. You can also slow a 115V AC fan down by connecting a cap in series with it (a plastic film cap of a few uF rated to take mains voltage)  
 
If you have trouble with noise and vibration, you can mount the fan on those rubber doohickeys you use for mounting reverb tanks. Works for me.  
 
Steve C.
 
5/22/2000 9:42 PM
Casey4s

Hmmmm, I never really thought about an AC 115/230 fan. That sure would make things easier. I will have to look around and see what I can find size wize. One of those little computer fans is the perfect size for the space I have available. I already intend to mount it in some kind of "shock mount".  
 
Thanks for the ideas guys, I hope to fire this puppy up next weekend ;o)  
 
Casey4s
 

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