Chassis ventilation - Worth the effort?

[soundguruman]

I can't figure out if you're trying to be a dick or be helpful

Of course your amp needs ventilation, and a fan would be even better.
The cooler it runs the longer it will last, and it will make the tubes last longer too.
I have been using 12VDC fans and running them on 7-9 volts.
This keeps the noise at a minimum.
I try to use Evercool, aluminum frame case fan, because it's not plastic.
80-120 MM
Don't use a filter it blocks the airflow. But do use a fan guard, and protect your fingies.
The reason manufacturers don't use fans is that they are trying to maximize profits.
They also want the life of the amp to be short, so you will buy more amps, and more tubes.
Almost any amp would benefit from increased cooling, of course.

[Gaz]

Ok, thanks that is helpful! For tubes, is it optimal suck the hot air away or at the tubes?

[soundguruman]

Ok, thanks that is helpful! For tubes, is it optimal suck the hot air away or at the tubes?

In a tube amp, the tubes get very hot. Much hotter than a transistor amp. The tubes don't have a heat sink.
In that case you wanna blow cold air into the tubes. Because........the fan blades and motor can overheat when you suck heat out.
Unfortunately, all the fans have plastic blades, and the motors have lubrication that will break down when they get very hot.
So by blowing air IN, the fan always stays relatively cooler than sucking heat out.
And then you have your fan INTAKE, there must always be an exhaust vent too, where the hot air exits.
And the best place for the exhaust is the TOP of the case. Heat rises, although many manufacturers seem to have forgotten that.
The next best place being a rear exhaust.

What I was trying to demonstrate when I was being a dick, is that the designer put the vents there for a reason.
These vents are not for show.
When somebody decides they don't need the vents, they have decided that they know better than the designer.
And usually they don't know more.
The Hiwatt is one of the most beautifully built amps ever. It is an example of masterful craftsmanship, reliability, and design.
And it costs Hiwatt plenty to punch out those chassis vents. Why would they spend the money if it was not needed?

But then there are plenty of transistor amps, not Hiwatt, where the designer assumes heat travels DOWN.
The transistor is on TOP and the heat sink fins are pointing down.
Now we do know better. These are the amps that last about as long as the warrantee, then POOF.

[Gingertube]

That HIWATT Chassis picture is an excellent example of how to do the venting.
It (as shown) does 2 things:
1st it allows convection air currents around the hot devices (tubes in particular) to keep them cooler.
2nd it restricts the paths (from the local hot devices) by which heat can be conducted to other parts (this is the action which is often forgotten).

Note also that heat shield (vertical plate) which blocks tube heat from the components on the other side (Electrolytic Filter Caps in particular) - another simple but excellent idea.

Reeves built stuff to MIL SPEC or at least his builds were heavily influenced by his previous experince of of MIL SPEC construction and wiring.
Probably one of the best examples to follow when planning layout and construction.

If you need extra cooling:
A rectified 6.3V AC Heater supply will give you around 8 Volts DC.
A 12V DC Fan will run slow and quiet on that supply but give sufficient flow to assist the convection air flow.
Accoustic Fan Noise is minimized AND fan efficiency is maximised by blowing into the chassis, never try to suck air out of the chassis.

Original Question:
Worth the effort? - Absolutely, unless you are a commercial builder who is only interested in the amp lasting 3 weeks longer than the warranty period.

Cheers,
Ian

[soundguruman]

That HIWATT Chassis picture is an excellent example of how to do the venting.
It (as shown) does 2 things:
1st it allows convection air currents around the hot devices (tubes in particular) to keep them cooler.
2nd it restricts the paths (from the local hot devices) by which heat can be conducted to other parts (this is the action which is often forgotten).

If you need extra cooling:
A rectified 6.3V AC Heater supply will give you around 8 Volts DC.
A 12V DC Fan will run slow and quiet on that supply but give sufficient flow to assist the convection air flow.
Accoustic Fan Noise is minimized AND fan efficiency is maximised by blowing into the chassis, never try to suck air out of the chassis.

Cheers,
Ian

That's a cool post.

[Gaz]

Yeah thanks guys for the helpful suggestions and info, I think I'll probably go with the fan route if anything.

I just thought maybe the chassis venting could be done better by allowing a way for air to flow through the chassis rather than just rise out of the little slots. I'm also wondering if it was so great then why didn't they do it on all their amps?

[defaced]

I just thought maybe the chassis venting could be done better by allowing a way for air to flow through the chassis rather than just rise out of the little slots. I'm also wondering if it was so great then why didn't they do it on all their amps?

Is there a clear use for the round holes at the front of the chassis? If not, then I'd say you've got a ventilation circuit going on.

[Gaz]

Is there a clear use for the round holes at the front of the chassis? If not, then I'd say you've got a ventilation circuit going on.

Good point, I'd bet those are there for the same purpose, but I don't know about ventilation since Hiwatt cabs have no grill or anyway for air to get in the front. I don't know if I understood you correctly, but thanks for pointing that out.

About adding a fan, I've been doing some research about positioning the fan, but can't find much info about good specs for the application. I know I'd like to use a 12VDC fan, but I don't know what good CFM and noise ratings are as well as bearing type.

Thanks.

[defaced]

Good point, I'd bet those are there for the same purpose, but I don't know about ventilation since Hiwatt cabs have no grill or anyway for air to get in the front. I don't know if I understood you correctly, but thanks for pointing that out.

I'll step through what I'm thinking starting at the exhaust since that's where the "pull" is coming from.

1) The heat from the power tubes rises upwards and out the vents at the top and back of the head shell. Most of the heat will rise upwards, this will create a negative pressure on the vents around the base of the tubes. Note the upright metal between the power tubes and the preamp tubes. Many state this was done as a shield, but it will also act as a louver to direct air flow. This is important for later.
2) The negative pressure pulls air in from the inside of the chassis which creates a negative pressure on the holes at the front of the chassis
3) The negative pressure on the holes at the front of the chassis pulls air from the empty space inside the head shell, this creates a negative pressure on the air inside the head shell
4) The negative pressure on the volume of the head shell pulls air in from the vents, mainly the back vent because the top vent is expereincing positive pressure due to step one (air flow, like electricity, has to have a circuit) The metal shield that I said was important in the first step helps direct air around the transformers and into the front of the head shell space

I think the Hiwatt cooling system is more than just the vents, it's the entire layout of the chassis and components. If it isn't copied directly (or modified to be significantly better), just making holes isn't going to do you much good, though understanding how it works may help you with your fan layout to make it more effective.

So about your fan. Here's what I suggest, go to Newegg.com, look at fans there. Find one that has 8 bazillion reviews and great ratings, buy it. Yes, it will probably be plastic, so position it accordingly. I would advise getting the largest in diameter fan you can because it will usually have lower noise and flux (basically air pressure, you don't want a big thermal gradient from one side of the tube to the next assuming you'll be blowing these at the tubes sticking out of the chassis) for a given CFM rating. I seem to remember ball bearing being the prefered type, but a quick skim of a review site that has a "fan shootout" or similar will usually contain those sorts of generalities.

[Gaz]

Thanks, Defaced! I like your analysis. My layout would be quite similar, so I think I could get it to work. My only practical problem doing my own metal work would be making the oblong slots around the tubes. I know I've read before you've done a lot of metal work - any tips? I was thinking I could save my self a lot of filing by just drilling some 1/4" holes around the sockets...

That's a good idea of researching the fan as well, appreciate it.

[defaced]

You're welcome. Keep us posted on the development of the project.

[trobbins]

I've got a 100W PA amp from early 60's that has a very similar strip of 4x EL34's and rear plate. The valve sockets are sunk below the chassis (which is actually a right royal pain for allowing a good grab of the valve) but does allow the same sort of airflow scheme. With no fans in those days, and some electros and early SS diodes under the hood, the aim was to get as much free air convection from chimney effect as possible going on. Although my amp did actually have two damper diodes with 18W of heater power under-chassis as well, not to mention the 5-10W ww screen stoppers.

[soundguruman]

The screen stoppers don't get hot until the tube goes bad.

[trobbins]

Unless of course you enjoy a cranked amp at +11.

[J M Fahey]

I often use 12V PC PSU fans with rectified 6.3V .
Not really trying to blow air straight at the tubes, I may even put the fan at the other end of the chassis, in my case I find that just *moving* air there, even at low speed, is much better than any passive convection.
The inside cabinet temperature goes down to bearable.
Specially in amps that run *very* hot, such as Matchless.
Even a small CPU Cooler type, at reduced voltage helps.
JM2C