Cabinet Construction Question

[Mason]

I’ve got a question regarding cabinet construction. I’m building a head cab for my AC30 and if you’re familiar with the traditional head cab for these amps you’ll know that there is a gap between the chassis and the floor of the cabinet. The chassis sits on a board that can be slid in and out from the head cab, see photo for reference.



My question is, would there be any benefit to routing out a portion of the board so that the chassis has open airflow? AC30’s can run pretty hot so letting the chassis “breath” so to speak sounds like it could be a good idea. Is it worth the hassle?

If what I'm asking is unclear please let me know and I'll try to better illustrate.

[sluckey]

Anything to increase air flow in that cab is worthwhile IMO. Maybe just a series of 1.5" holes rather than one big opening. If I had that cab I'd mount a small 12V computer fan on that board. Power the fan from the filament via a FWB and 470µF cap.

[Mason]

Yeah, I was thinking about a fan too. Trying to figure out the best implementation for that. Do you think mounting the fan at the end of the board blowing air across the chassis would be best, or is there another position that would work better? There will be vents above the power tubes and transformers to let hot air escape.

[shooter]

why not make the back "heavy gauge metal screen", mount a fan there?

[sluckey]

I'd try to mount the fan to blow directly on the power tubes.

[thetragichero]

i took thermodynamics three times before passing so i could be looking at this totally wrong: should a fan be blowing on the power tube or sucking air from the power tubes like a pc with one exhaust fan?

[sluckey]

If all the air the fan would be sucking could be guaranteed to flow over the tubes then suck would be fine. I doubt that's the case though, so aim the fan at the tubes and blow. I never studied any thermodynamics.   

[shooter]

   shouldn't matter since the 3rd law says something like, it all descends to "crap" anyway 


on the last transmitter I worked on the squirrel cage fan sucked computer room air threw a filter and blew on the tubes
everything else in the room exhausted air

[2deaf]

If ceiling fans are any indication, blown is better.

[acheld]

It gets complicated, but the practical effect is the same in this case.

In the case of a computer, you have heat sinks mounted on the CPU and GPU, transferring the heat to a radiator, which is then cooled by a fan.   CPU/GPU will generate a lot of heat in a small package, as we all know, and the thermal design reflects this.

In this case, you're really just trying to remove hot air from the cab to allow more efficient heat radiation from the tubes.  So blowing it in the cab, or sucking it out doesn't matter, as long as you are exchanging hot air for cool air.  As for blowing air on the tubes themselves, there might be marginal benefit.     

My thermo courses were decades in the past, but to understand how much benefit, you'd have to measure the ability of the tube to transfer heat in various conditions.  (LOL, I'm not going back there.)  I am sure all this has been measured 70-90 years ago . . . maybe someone knows where to find the data.  It'd be interesting!

Now that I think about it, this topic has practical value for my hot EL84s . . .   

In any event, sluckey's heater circuit rectifier-->computer fan is a great idea.

[thetragichero]

i am of course unfamiliar with vox chassis/cabinet designs because they've always looked suboptimal/clunky to me but as long as you have well-placed air inlet ports sucking the air out would be my choice

[Willabe]

I don't think it matters much, in or out, as long as there's air flow/exchange.

I seem to remember reading (Kevin O'Connor?) that blowing air on the power tubes can cause noise.