Simple remedy to heat soaked amps!

[soundofvoid]

I use modified GTA SE-100 tube amps and the issue of reliability has always been a concern to me...
"Thermionic" is a old tube term that describes exactly that:you need heat to get those electrons fly!
Also massive transformers working on high voltage and resistor banks exude heat!
The result is a very hot device that a)Plays music the way no SS amp can!
b) works great as a heat source on cold winter nights!
c)It's internals operate in a very unforgiving environment that
stresses their reliability and shortens their life span!
Having the privilege to start the modification from scratch i had taken great consideration on dealing with the heat issues that tantalize every tube amp.
I have hand picked all parts to work safely up to 105 deg Celsius (e.g.most of the original caps
were of the common 85 deg variety),upgraded critical resistors to the next wattage level,
installed separate heatsinks on all big wirewound resistors,arranged wires away from overheated places inside the amp and sometimes moved parts so i could keep a constant air flow from bottom to top.All this worked nicely and have produced hot running but reliable amps.
BUT my mind was not at rest.Sometimes on hot days and long listening sessions i could measure chassis temperatures over 65 deg!That is an amp casing that is way too hot to touch!
Forced ventilation was troubling my mind but i had to find a way to implement it effectively.
A quick search in the net provided various solutions (in the form of 12V fans) and i had to pick a winner.After a lot of consideration i decided on buying 3 fans (12X12cm version) from Scythe.
These are model S-Flex SFF21D.
They are guaranteed for 150000 hours, work on 8000 rpm/12V,6000rpm/9V, consume only 0.1 amps on 12V, they have absolutely no vibrations and a noise level of only 8.7dbs!
This is all achieved with the use of a Sony patented "Fluid dynamic bearing".
Next step was to make sure that i had taken all reasonable precautions to make sure that no
electric "pollution" was entering the amps chassis.
I glued a round piece of copper sheet and mu-metal sheet to the center spinning core of the fan
(mu-metal to the core and copper to the amp)and i glued them on the fan side facing the amp.
Next i had to decide where exactly to put it!
Cutting the amps chassis was out of the question but the good thing is that the amps bottom is
"grilled" so i could force the air to come into the amp from the underside.
My amps are on dedicated platforms made from solid steel feet with bronze spikes and cups and 3 cm thick HDF shelves.Their weight is around 15 kilos.
With the use of a Parts Express sourced jig, designed to cut round holes in speaker baffles
i have cut 12cm diameter holes through the HDF, exactly where the amp needs the most cooling
(in the middle of the right side).The fans were screwed on position from the underside of the HDF
with a in-between layer (2mm) of silicone.
A small multiple voltage (15-12-9-6V)power supply was used to power up the three fans.
Without the amps in position, i could hear nothing from a distance of 30 cms from the fans.
I placed my hand on the platform and again could feel no vibration at all.
The amps weigh around fifty kilos each and could certainly damp a little vibration with their mass
but it's a good thing to start without vibration at all!
Then i placed the amps on their position and fired up everything.
Tubes are very picky with vibrations and EMI and although i had taken every precaution you can never know what will happen...
I couldn't hear anything - not from near the amps and certainly not from the speakers.
I turned on and off the fans with music program playing and without, to see if there was any difference, audible or other...
I couldn't detect one!
Of course the real test is the temperature drop and after a four hour high volume listening
i can report that the chassis was never more than 45 deg!I could not expect anything better!
If anyone of you has similar problems with heat soaked tube amps or even class A SS amps
this is a solution that you could seriously consider.It's cheap, easy to install and works!
Of course before you cut any holes in your rack you should check with a working fan in hand
to see if your equipment picks up noise from the fan.If not, you can go on and do it!
Success is guaranteed!
If someone has another solution to the problem, all of us would love to hear about it!

 

[soundofvoid]

And here is a little photo show of the parts and process:
A) The type of 12cm fan used for cooling.
B)The router with the jig for cutting perfectly round holes.
C)One fan in place for my right channel amp.
D)With the amp in place nothing can give away what is happening underneath.
E)View from the underside-not very easy to take this photo.

 

[kach22i]

Cool, thanks for the photos it makes it clearer for me.

 

[soundofvoid]

And here are two more: A simple "walkman" type 3.5mm mono female plug was inserted in the power line coming from the 12Volt power supply.From there with the use of a similar male to female Y adapter i divided the power to the two lines.(Attention:these are audio, not power plugs but they can deal with the minute power requirements (0.1 A) of the fans.I had them lying around,so i used them!If you use such a simple solution remember to preserve polarity and to FIRSTLY connect all plugs BEFORE turning the power on!Plugging/unplugging with the power on, will cause a short circuit and probably blow a fuse in the power supply or disable a fan!I also installed a simple switch before the PS so i can turn it on/off without having to pull the plug.
Another small detail regarding the placing of the fans into the round holes is that the fans have "ears"
in both sides.From the side facing the amp, these ears have to be cut so the round part can be inserted
in the hole.Make sure that this is a tight fit so that there are no air "leaks" around the hole.
Voila!That is all...

 

[amirm]

[posting this here also just in case people don't read the duplicate in the amp thread]
Great write up although if there were more paragraph breaks it would make it easier to read .

I have hand picked all parts to work safely up to 105 deg Celsius (e.g.most of the original caps were of the common 85 deg variety)

This is great advice and generic to many more situations. Caps are made up of chemicals that create the functionality of a capacitor. Put them next to something warm though, and the chemicals dry out, losing their functionality. The caps look like this btw:

Look at the top of any of these electrolytic caps. If it is not flat but bowed out, it means the above has happened to it.

As noted, caps come with different temperature ratings. In a tube amp, they must be the 105 degree variety. Anything else is criminal . It is a hot environment and even if you don't hit 85 degree, it is still warm enough to dry it out over time, significantly shortening the life of your gear. Once the cap goes, it might take other devices with it!

The issue is not limited to tube amps. Next time you are buying a PC power supply look inside it and see if you can see the cap temp rating (it will be either 85 or 105 as mentioned). If it is 85, put it down and don't buy it. Likewise, if you ever buy a piece of electronics and have the opportunity to open and see the inside, find where the heatsinks are and look next to them. If there is an electrolytic cap very close to the heatsinks, then it is a bad design. If the rating is only 85, then it is a terrible design!

Here is a picture from a short little article explaining the same:http://images.google.com/imgres?img...&ndsp=21&tbs=isch:1&ei=TZrhS6jiDojAmQP_sKz-Dw

You can see the 105 degree rating after the PL letters (which don't mean anything). Just look for degree C symbol and the number next to it is the temp rating.

There may be more elegant solutions out there but this one works,it's cheap and you can
do it easily on your own!

This is a very good solution. The only thing that would make it better is an alarm that would tell if you if the fan is stuck. The problem with active cooling (i.e. using a fan) is that when the fan stops, it makes the situation worse than no fan at all. The fan blocks convection so damage occurs that may not happen otherwise. You are using pretty high quality fans but still, failures occur, including the wiring or the power supply to the fan.

If you have an automation system like Crestron/AMX, it is easy to wire that up to provide this feature (path I am taking). Otherwise, the circuit is dead simple and you could build one yourself if you are handy at all with soldering iron. There are also various temperature activated sensors that could be used to say turn on a buzzer. All require some type of DIY skill but that is what this thread about, no?

 

[soundofvoid]

Nice idea Amir!A buzzer connected to a thermal trigger!I will look into it!I only hope i can hear it when listening at high volumes...
Maybe it's better to trigger a pulsing high power led!You can't miss that!

 

[Gregadd]

A flashing LED might also work.

 

[nsgarch]

Cooling my MC275 w/ case fans

Here's my cool McIntosh MC275. I use two 80mm 12VDC double ball bearing case fans http://www.vantecusa.com/en/product/view_detail/111 (Vantec SF8025L Stealth, $10 ea.) wired parallel to a RadioShack 9VDC wall transformer (9V to slow them down a bit.) They're inaudible from 16" away. The cage stays at room temp. and even the power transformer remains barely warm to the touch.

They blow upward, drawing air thru the front of the cage as well as from under the chassis (and up thru the tube chimneys.) I feel it's better to exhaust the hot air buildup from inside the device, rather than to blow cool air at the glass tubes. Also, by doing it this way, the velocity of the air entering the amp (at many different places) is much too low to pick up any dust.

It's heat buildup that destroys equipment. By using exaust fans, the tubes, trannies, etc. operate at the same temperature as they would without fans, except the heat they throw off is removed immediately, instead of building up until convection can remove it -- and convection isn't always enough in certain situations.

The only company I know of that blows air right at the tubes is Audio Research; and I can say from personal experience, it's better to exhaust the heat.

 

[soundofvoid]

That's a nice one!An MC275 with double exhausts!What is the clearance from the top of the tubes to the cage roof?
You could fabricate another cage (i guess you don't want to mess with the original one) ,perhaps a bit taller so that you
could incorporate the two fans so that their bulk would be under the top producing a nice flat top surface...Just an idea...
I agree that it is heat that produces the most problems in tube and class A SS amps.
If you want your gear to last this is a top priority issue to deal with...

 

[MylesBAstor]

Here's my cool McIntosh MC275. I use two 80mm 12VDC double ball bearing case fans http://www.vantecusa.com/en/product/view_detail/111 (Vantec SF8025L Stealth, $10 ea.) wired parallel to a RadioShack 9VDC wall transformer (9V to slow them down a bit.) They're inaudible from 16" away. The cage stays at room temp. and even the power transformer remains barely warm to the touch.

They blow upward, drawing air thru the front of the cage as well as from under the chassis (and up thru the tube chimneys.) I feel it's better to exhaust the hot air buildup from inside the device, rather than to blow coo; air at the glass tubes. Also, by doing it this way, the velocity of the air entering the amp (at many different places) is much too low to pick up any dust.

It's heat buildup that destroys equipment. By using exaust fans, the tubes, trannies, etc. operate at the same temperature as they would without fans, except the heat they throw off is removed immediately, instead of building up until convection can remove it -- and convection isn't always enough in certain situations.

The only company I know of that blows air right at the tubes is Audio Research; and I can say from personal experience, it's better to exhaust the heat.

I agree. Years ago used fans in the sucking manner for some old cj amps. Put the fan on top, used some rubber damping compound on the bottom of the fans to quiet and dampen and hooked them up to a variac.

 

[kach22i]

I thought that for negative draw fans to work you need to seal the path from intake opening to exhaust vent.

You are really creating a vacuum or difference in air pressure type system.

 

[MylesBAstor]

I thought that for negative draw fans to work you need to seal the path from intake opening to exhaust vent.

You are really creating a vacuum or difference in air pressure type system.

Always kinda thought heat rose

 

[kach22i]

Always kinda thought heat rose

It does, but fan draw is still fan draw.

Now if you mean to say the flow into the fan is increased by the flow of rising air, then fine. However if that flow is not of adequate pressure the fan will draw air in from the nearest source, which is at it's perimeter or sides and that includes above it (and above the cage) and all around it equally.

Like a car's radiator fan shroud.
http://www.car-stuff.com/fanshroud.htm

As the fan shroud holds the fan securely in position, it facilitates highly efficient dispersal of heated air that is then released from the coolant.

Single with shroud (homemade a lot of work for nothing?):
http://www.rx7club.com/showthread.php?t=808292

Single shroud:
http://www.mcjackscorvettes.com/newaftermarket.htm

Dual with shroud:
http://www.macsradiator.com/browseproducts/27-inch-puller-fan---shroud.HTML

EDIT:
In architecture there are/were negative pressure toilet exhaust fans which pulled air from a fan on the roof (in large multi-story buildings). However one little leak in the system and it pulled air in from the air leak typically in the attic and not in the stinky toilet room. Positive pressure fans pushing the air (located in the room not roof) and not pulling the air end up being more fool proof and specified by engineers/architects and are more common now.

 

[MylesBAstor]

It does, but fan draw is still fan draw.

Now if you mean to say the flow into the fan is increased by the flow of rising air, then fine. However if that flow is not of adequate pressure the fan will draw air in from the nearest source, which is at it's perimeter or sides and that includes above it (above the cage) and all around it equally.

Possibly but it did seem to work. It might be also that the cage is not totally open and that helps.

 

[nsgarch]

I thought that for negative draw fans to work you need to seal the path from intake opening to exhaust vent. You are really creating a vacuum or difference in air pressure type system.

Ducts and shrouds are not necessary in this case. Here, the cage itself acts as an exhaust plenum. Since only two of the six sides of the plenum "box" are perforated (the front side and the top side the fans sit on) even at low fan speed, plenty of vacuum is built up inside the cage. You are not incorrect, but intense vacuum is not required in this situation. Only a slight negative pressure, enough to assist/boost the flow resulting from natural convection, is sufficient to keep the whole amp quite cool.

 

[kach22i]

enough to assist/boost the natural convection

I'm sure it does that and does what you want it to - and helps.

Just trying to clarify the engineering concepts a little.

 

[nsgarch]

I'm sure it does that and does what you want it to - and helps. Just trying to clarify the engineering concepts a little.

??? What "engineering concepts" are you referring to here? Are you implying my solution is somehow unsound, or even (God forbid!) sloppy?!

Actually George, I think this solution is quite elegant as an "engineering concept" . And actually more effective than the two possible extreme solutions: 1.) your ducted exhaust fan (fussy to build and with lots of air intake noise) or 2.) an 'amplifier-sized' exhaust hood (which would only keep convection heat from getting into the room, but not cool the amp.) As a design architect, I take great pride in my ability to take ordinary textbook technology and make something more sublime out of it

. . . . . any technician
can light up the nighttime.

But only an artist
can light up
the day . . . .

 

[kach22i]

Actually George, I think this solution is quite elegant as an "engineering concept" .

I like what you did, and I bet it works. The alternate solutions would be very messy.

I also like what "soundofvoid" did too.

One is push, one is pull but they both get the job done in a clean way.

 

[Gregadd]

Always kinda thought heat rose

Heat radiates 360 degrees. Hot air rises.

 

[soundofvoid]

This is the part where your Mama comes in yelling:"You all shut up!Just eat your cake, drink your lemonade and go out to play!"