21st Century updates for a KWS-1

Since I acquired a KWS-1 and PS from the scrap pile, while restoring the unit I am considering updating some parts of the setup, with 21st Century updates. This rig is no Virgin, missing original parts and might just work better when the mods are completed.

1 of the main problems with the KWS-1 combo was the forced air cooling setup of the PA tubes. The original Collins setup has a blower motor unit consisting of a 5 1/2" diameter by 1 7/8" wide blower fan, mounted to a 115V motor. The motor I am guessing spins about 3K (?) RPM, as I can find no information on this. With 1 1/2" ID air duct being used between the blower motor and the PA cage. Even with my shoddy ME skills, it is easy to see this factory setup was lacking severally. Has anyone ever operated a KWS-1 where the PA tubes weren't frying eggs at the same time?

With the 250Bs installed in the final PA cage, each tube needs 6.4 CFM of air being pushed over it's fins according to the spec sheet. With 2 tubes in the cage that comes out to 12.8 CFM to cool the tubes properly at max. With the size of the factory blower motor setup, CFM capacity of the 1 1/2" ID duct and the rather large frictional losses (90 deg elbow) in the PA tube forced cooling system, it is easy to see why the KWS-1 suffered from serve PA tube heat problems. The main cause of why the S-1's VFO isn't as stable as the A-4s are? The CFM capability of the 1 1/2" duct is under 10 CFM with the factory blower motor setup in the PS. That is with no frictional losses. The frictional loss of the 90 degree elbow, can be as much as 30% in some cases. That is 1 reason why the PA section gets mighty toasty.

There is another reason why the factory forced air cooling system is inadequate. The blower motor setup is sucking in far hotter air, then the ambient air temperature is at, that resides in the PS's oven like box. Then it blows this hotter air across the tubes to cool them. If it had a ambient temperature, fresh air intake system, the PA tube's forced air cooling system would be more efficient. The blower setup can actually be moved in the PS box to the left and back. Drilling new mounting holes and tapping them out isn't much of a problem. This would help facilitate a fresh air intake system.

With today's blower setups, such as the 1s being used for wood stoves, you can get more then enough CFM output to cool the 250Bs. These units are actually a little smaller in size then the original Collins factory unit and run off 115V. Using 2" ID vinyl duct hose and softening the frictional losses, with either 2 @ 45 degree elbows or a plenum chamber mounted to the outside the PA cage will help cool the tubes more efficiently also. The plenum chamber will provide a higher constant static pressure then the factory setup did, cooling the PA tubes more efficiently. The newer blower setups are rather cheap on Zoro's website. (Grainger) The vinyl duct hose is the same stuff being used a coin operated car wash vacuum setups and is very tough stuff. The purists might be wringing their hands about this mod, but if it makes the rig preform better, it's worth considering, I reckon.

 

I took the original blower setup out of the power supply and cleaned it up. The piece looked original with the fan motor a 1950s piece of iron. Steel round fan blade and a steel cooling impeller on the back of this electric motor. Heavy duty piece but with a fan exhaust opening of 1 7/8" X 1 7/16" wide, it can't produce the needed CFM to cool the tubes properly. I will use the original blower motor mounting pedestal, as that is still more then robust enough to handle the new blower motor setup.

I can see why the blower motor setup was mounted as it was from the factory. Art and the boys wanted a straight shot from the blower exhaust to the 90 deg. elbow that the bottom of the air duct was connected to. Since the blower setup of today can be mounted in any orientation, the actual exhaust port of the blower motor can be orientated so that it is pointing straight up to the PA tube cooling chamber. The bottom 90 deg elbow will be eliminated from the system and the air flow will have a straighter shot to the PA tubes. The blower motor will be sticking out a touch and a little sheet metal work will be in order, but the plasma cutter will make short work of that. Today's blowers are very quiet so noise shouldn't be a problem either.


Art was all about performance in his radios, I don't think he minds someone 60+ years down the line, improving/restoring 1 of his rigs to get it back on the bands.

 

Here are some pics of the original blower setup.

 

Having just acquired (and still getting it runing) a KWS-1...

...it seems to me that the most you can do with cooling the 4cx250s is going to be determined by
the available "window" that the plate fins form. That's a restriction. So, all you can do is to put
pressure behind the air. The more pressure you can build, the more air you can push. It's a matter
of velocity, not volume.

The blower is intended to work into a back pressure - it's not a free flow situation.

So, I doubt that the hose or the bends greatly effect the cooling.

If the blower is going to get changed, it would need to be one whose spec for not just CFM, but
one where the pressure for a given flow resistance would be higher.

 

100% correct, if you go with the stock factory blower location setup. Static pressure is measured in water inches. For such a tiny blower system such as this the water/inch ratio is .5 or lower I am guessing.

So how do you bring this blower setup into the 21st Century? Time to think outside of the box literally? The simplest and easiest way to build static pressure in a air/cooling system is to make the duct work as short/small as possible. What would even be better, would be having no duct work at all, with the blower right there, next to the tubes themselves. A inline blower's exhaust port can be pointed directly into the cage to maximize static pressure, I reckon. Something along the lines of a inline bilge air pump on a boat. Those units are way to big to be used here, I will have to find something used in an appliance application it looks like. Shouldn't be hard finding a 12V source for the blower setup in that 250 LB PS. 3D printing might just come in handy.

There won't be much problem of back pressure forces in the PA cage either, which is a very good thing. Once the air from the blower crosses the cooling fins of the 250Bs and gets heated, it will rise along being pushed over to the large vent area behind the big caps. The hoter air will flow towards the cooler air just as it always does. With moving the blower closer to the tubes, you can use a smaller blower unit to get the job done. So you can have a nice quiet blower assembly and still get the job done in the PA tube cooling area. No sense in hacking up this classic I have decided, as it does kind of grow on you when you spend some time with it.

 

I never really though the original blower was not good enough.

I did have to remove mine and clean it up. Because the blower would not come up to speed. That was many years ago.

The air hose looks like a radiator hose from a tank. It is fairly quite for the amount of air that it moves.

I think one thing that some may do, Is power it on with no hose or the blower does not start up properly because of old age and setting unused.

Have Fun.

 

Being no expert in matters of air flow, I offer an extremely questionable opinion...
... seems to me that the location of the blower makes almost no difference. The reason
this seems correct to me is that the hose and that volume "looks" like a reservoir more than
a resistance. Once the pressure in the hose, no matter what length is reached and becomes
essentially equal at some level it simply "bleeds" off through the 4CX250. As far as I can see
the only way to get more flow through the tubes, regardless of where the blower is (pretty much) is
to increase the pressure of the incoming air.

This assumes that the volume that the blower can move is sufficiently greater than the volume
required to pass through the tube fins, which I think it is.

The only reason that I can figure that might effect this is IF there is loss of pressure due to frictional
forces in the "transmission" line, aka the air hose. But assuming there is not that much, then the
determining factor will be in the vast majority only the pressure that a given blower can produce...

 

You can use the output of a Henry to get plenty of air flow.



May be a bit of a overkill, A Henry feeding a Collins.

 

You have to remember then even air has some weight to it. For clean dry air at sea level it works out to about .075 (?) lbs per cu ft if I remember right. So you have to take this fact into account. If you have a 3 " round duct that is 1' long it might have say 10 CFM inside that duct. If that duct is now 100' long you have 1000 CFM of air that now needs to be moved by the blower motor. If you want the same airflow rate coming out of the 100' length of duct as the 1' of duct you will have to increase the CFM and static pressure of the system to make that happen. The heavier an object is the more force it will take to move it.

If you have a water hose that is 10' long and another 1000' long both of the same ID and water head pressure at the hose spigot, which length hose will have the fastest flow rate at the opposite end of the hose spigot?

 

Lets go with the known facts. How much CFM and static pressure can be produced by a Collins factory blower fan blade setup that is 5 1/2" in diameter and 1 7/8" wide and spins at 3k RPM? Take it up to 4K RPM makes little difference. What is this figure?

Once we get the CFM/static pressure rating of the Collins factory blower, it should be easy to calculate the CFM airflow rating of 1 1/2" ID duct at the Collins factory blower static pressure rating. What is the number for this calculation? Does this figure come out to more the 15 CFM at the end of the 40" duct length while passing thru 2 @ 90 degree angle elbows into the PA cage itself?


Since the 250Bs have almost a 400 degree F anode rating, what do you believe would be a good operating temperature for the tubes in the PA cage, if the PA tubes received the proper forced air cooling?