RIG COOLONG..SUCK OR BLOW?

[ve6pg]

..hi from tim...what is your opinion of cooling a rig?...remove the warm air, or blow cool into it?..and i dont want to hear about water cooled !

tnx..

..sk..

[WBear2GCR]

A bit depends on the rig the tubes, the sockets, the amount of heat and the layout...

In a Heath Apache they blow air with a fan inside the RF cage - the fan is running on one of those open frame AC motors, so
not much of a fan... the Johnson Valiant II has no fan. I put a small whisper fan to blow air across the modulator iron and the mod tubes.

Some rigs like the ceramic power tubes all use a pressurized lower chamber to blow an even flow of air through the fins, out and up... this is a very good way to cool, but depends on how the rig is set up. It has to be set up so that the lower chassis (or sub-section) can be pressurized and the air has to be directed up and then past the things that need cooling... one problem is that the squirrel cage blowers for this can be noisy.

You can use a larger one that is slowed down for less noise and less higher freq noise, but then you have to find a way to deal with a larger blower! You can find small blowers that put a lot of air out, but they wind up like jet planes!

Fans don't work well into back pressure, so blowers are needed for pressurized chassis setups (usually).

Oh - both of these were blow examples...
Suck works if you only need to clear out the hottest air from a cabinet... and works best if there is a good air path between the inlet point - then the thing that needs cooling - and the outlet (fan)... you see this on equipment racks quite a bit.

What rig do you want to cool? Maybe a jpeg?

                           _-_-bear

[K5UJ]

The design I like best is a little of both--the cabinet and fan or blower is set up so that it draws air in through things that might need a moderate amount of cooling if any, such as the power supply area, then blows out forcing air past the things that really need to be cooled, i.e. the tubes, either up through chimneys (better in my opinion) or across them if they are glass. 

The design that is better than all that is the one that doesn't need a blower at all (but you didn't ask about that).

[Opcom]

I can only speak from experience having tried all kinds of ideas. I have used both methods including taking air in at the top and exhausting it out the bottom of a rack. Despite the wailing of some engineers to the contrary, this does work if done right (a la Microvax 3300, 3900 still alive in my lab and 20 years old). OK that is only a 500 watt computer but it is not about what is being cooled, only the ways to do it.

Aside from the need to specifically treat tubes intended for forced air cooling, I prefer to have a well sealed cabinet and push cool air in, and direct some of it specifically, and let it out thoughtfully, making it do the most work.

To do so, there must be definite inlet paths for cool air designed in such a way as to cool the entire instrument evenly. It is not always easy to just add a fan and expect job done.

The biggest rig here has two internal blowers, taking inside air, pushing it through the tube sockets and and exhausing it inside, 2 FT away more or less. Then there is a large blower on top sucking hot air out of the rig so that the internal stuff always has cool air and the cool air is drawn in from the back though louvered doors. This also cools everything else inside.

If you are retrofitting, it is possible to create an (partial or full) air labyrinth from card stock, plastic, bakelite, or PCB material, so that the airflow is required to pass across certain components such as a transformer, heatsink, and power resistors. I did this with an old 4-tube type CB leenyar. All top and side vents were blocked except space for fans, and two fans were put there right above the tubes blowing down. Of the bottom vent, it was left open. This sounds weird but the amp and tubes ran pretty cool. Enough turbulence was generated to keep the other components reasonably cool and all was much cooler that the original no-fan design. This lived in the trunk of a car in Texas for several years.

If the top is perforated with many small holes, it becomes complicated unless you shamefully cut a hole. Alternately a square frame can be made the same size as the top, and you fill it with fans that blow air upwards. It is very difficult to blow enough air down through a perforated cover to do any good without a lot of noise

If there are vents on the bottom, a small 2" tall "fan deck" can be made that the item can sit on and air can be blown up into it. Care must be taken so that air can blow up around the tubes, etc.

If it is practical only to draw air from the item at one point, and it is the case that the item has well defined air inlets elsewhere, an internal fan can be put in to circulate the air inside more completely mixing it so that the temperature will be more even inside regardless of where the exhaust fan is.

If there is but one fan for the entire unit, try to channel air over the components starting with the ones that run coolest, end ending with the tube or the hottest one as the air exits.

I do not put plastic or cheap fans sucking out right over large tubes. It is not the hot air but apparently the invisible radiation of heat that will overheat the fan motor.

If the gear is physically large like a rack and dissipates at the KW level, find a blower from a 6000 series VAX minicomputer. I am not joking. Quiet at 12VDC, moves a ton of air at 24VDC. The centrifugal turbine-style fan comes with a rectangular or trapezoidal plenum and can be separated from that. It is meant to stand vertically but I have run them horizontally, plenum down, on tops of (well-sealed) racks and they do a very good job. Almost no one uses those machines any more and there ought to be lines upon lines of them sitting there gutted for the boards by now. sadly.. but the fans live on.

If you choose to take air in from the floor, try to take it from about 1 FT above the floor, through a grille/panel(s), and have the hot part of the equipment start above that, so as not to suck up the dirt from the floor. i.e. put the iron on the lowest level and draw air in above it for the MV rectifiers and bleeders ets.

To avoid the dust issue I have also done a few well sealed racks where the blower takes air from head level and moves it down through the rack and exhausts beneath the lowest equipment, or under the rack to the floor, the casters making the exhaust space. When blowing cool air down, it is important to have as much turbulence insde the enclosure as possible so that there is no question that everything is cooled. This does not mean a gale of air at each item, but it does mean a breeze. It is easy with SS gear that has heatsinks, but planning is necessary for tube gear where there are many diverse hot things. A cigarette will indicate spot air movement if there is any doubt. or a wet finger but that is less effective if the breeze is slight. The point is to provide more movement than convection. Even just a little more is useful for minor items like a 12AX7 etc. especially if in a shield.

In the case of the pictures there with top mounted blowers, if there was a tube inside that required "air system socket" cooling such as a 3-500Z or 4CX250, no special considerations would be necessary other than to cycle cool air through the cabinet so that the special device's blower would always have cool air to draw in. Otherwise, a dryer duct hose or a few smaller hoses could be attached to the backside of the dual squirrel cage blower, and half the blower air sent to just the high power section(s) or any hot spots.

If you are building the equipment, all the options are yours for cooling and you can consider all kinds of flexible solutions. Whether to blow or suck, all that matters really is that moving air touches everything and that the air volume has either a definite entrance or a definite exit. If the heat load is considered, and the blower sized for the air volume volume in CFM to remove x BTU/Hr. of heat at Y temperature rise, then anything will do.

If you have pets or a dusty place, use a filter. The metal mesh kind is washable.

[W2PFY]

..hi from tim...what is your opinion of cooling a rig?...remove the warm air, or blow cool into it?..and i dont want to hear about water cooled !

Tim, what rig do you want to cool? Maybe someone has done it. Maybe that person will offer you the answer? That's a very broad question.

[W1RKW]

sucking heat through the fan may not be good for some fans or blowers.

[Ed/KB1HYS]

Filter over the intake regardless of method.  Dust and crud will reduce cooling efficiency, and makes maintenance a pain. 

[ve6pg]

..well, one rig is a kenwood ts950sd, which i use fer cw, and general listening...it just seems to be getting hotter the last few months...the other is a viker 2...

..sk..

[K1JJ]

I'm not sure this directly addresses your question, Tim, but maybe others can use this info...

With most external anode tubes, air should be forced thru the bottom to top. I learned the hard way. Sucking air out the bottom of the tube (vs: blowing it into the bottom) is bad news. The tube seals on SOME tubes are physically bypassed by the air pulled through the fins when run "backwards". The seals get air starved. I burned up a nice tube doing it once.  It's so much better to have air blasting directly on the seals. Those seals can get pretty hot with just filament power and allow gas to enter in extreme cases. After just a few months of abuse, my tube shorted under HV - bang! Lice all done.

However, it IS quieter to suck air out rather than push air in. The turbulance at the tube anode seems less from noise tests I've done.

Glass envelope tubes may and may not have this problem if air is pulled from the bottom. Try it and see if air can pass onto the seals and keep them cool with the fils on.


In contrast, the best way - blowing air in thru the bottom puts the COOL air directly on the seals and then works its way up thru the plate fins or glass envelope.

Pulling ventilation air out of the cabinet is another matter and is always a good idea - IF you can stand the extra noise.

T

[Pete, WA2CWA]

..well, one rig is a kenwood ts950sd, which i use fer cw, and general listening...it just seems to be getting hotter the last few months...the other is a viker 2...

..sk..

The 950SD has a fan in it. Check it; maybe it's not working or there's a lot of accumulated dust and critters that are restricting air flow.

Viking II: Get a muffin fan 3 or 4 inches square (voltage your choice); position it to suck; put 4 rubber bumpers on each corner; set it on top of the cabinet over the finals. Sucking keeps the dirt and dust out of the inside enclosure. I've run my Valiant, Viking II and Apache for years like that after the Apache fan (it blows) got noisy and I had to shovel out all the dust bunnies that were in the final enclosure.

[ve6pg]

..all good stuff...i think i will open up the 950, es see what's what in there...tnx guys..

..sk..

[Opcom]

The question was broad and required a lot of detail to even halfway cover. haha only to find it is a classic 100W radio that shouildn't be modified.

I'm not excited by the perforated lid of the viking II from a top cooling fan point of view. It would be made more effective if a foam seal or bead was put around the perimiter of the fan to help more air to be evacuated through the perforations and avoid side-suckage. Elevating the sealed fan to 1/2" will also improve efficiency as the center hub of the fan does not help the situation if close to the perforated panel. But whatever, anything is better than no fan and many people do exactly the fan-on-grommets thing for desktop radios. My defect is a like for overkill.

[Ralph W3GL]

      Actually, as I recall, the TS-950 has two fans in it just like the 940 an earlier 930.
      One in the power supply area that is programed to run at all times and one in the
      RF final area that works from a thermister to run the fan when the sink reaches a
      given temp.

      The setting of the temp  is adjustable and should be described in the maintenance
      manual.

      One caviot: those crappy fan moters are prone to fail with heavy use!  I have replaced
      4 or 5 of them between a 930 and my 940 since 1993.  Granted  the 930 ran 24/7 and
      the 940 did the same for 6 years till I dumped the Winlink operation here.

      Kenwood tells you to lub the shafts at least every 6 months.

      Good luck Tim.

[Pete, WA2CWA]

Yep, two fans in it.
From East Coast Parts:
Discont.    F07-0887-04       COVER (REAR FAN) TS-950SD             
Discont.     F09-0423-05      (D) FAN TS-950SD


Rear shot of TS-950SD:

[WBear2GCR]

so, lemmmeee seeee... maybe I can sum this up??

Ya gotz ur single ended pushing, ur single ended pulling and yer push-pull blowing/sucking AIR combination??

OH GEEE!       

I apologize it is late at night.

                    _-_-bear

[KM1H]

If its like the 940 you can change the PS fan speed and the PA module on temp. I did that in the 90's to both my 940's otherwise they fry in heavy contesting.

Also both fans and heat sinks easily get crudded up and they do require occassional lube.

Carl

[WU2D]

Filter over the intake regardless of method.  Dust and crud will reduce cooling efficiency, and makes maintenance a pain. 

Great advice Ed. This is the key to not having to clean dust out of rigs - computers etc...

Filters are easier to clean than the whole radio!

Mike WU2D