3 phase blower on single phase how to?

[KA3EKH]

Bearings, balancing and the entire like are good but a one horse 3400 RPM blower is going to drive you out of the room! Don’t know what your requirements are going to be for that PA tube but I recall in a couple of the low power TV transmitters that I use to take care of in the analog day (5kW) that’s the blower that they used and it was good for fifteen inches of water thru a six inch duct. But you’re a big guy and should be able to take it, the noise at least. When they are set up right vibration was not a big deal and in continuous service they ran for four or five years before having to be replaced. Near the end of analog was replacing all the blower motors with Baldor units that I think were built in China that cost less than repairing the American motors and were just as reliable. If noise becomes an issue you can always put the blower outside or another room and use six or eight inch duct to connect, I never did that being every transmitter I work with was always in an unmanned aria but there would be something to be said for having air ducts and motors that start in another location when you turn on the transmitter.
Looking at the schematic I just wanted to warn you about what will happen if somehow your HV gets shorted to ground R6 and R15 will open dramatically! The same TV transmitters that I was talking about above had a 10 Ohm 225 watt resistor in series between the HV- and ground and when the PA tube would short out with 5Kv on the plate that resistor would explode. The stupid French tetrodes that they used would occasionally dead short every now and then and that ten ohm resistor was a sacrificial component to prevent real damage to the power supply, so of course it was installed down between the HV filter capacitor and input choke so there you were in the middle of the night fishing around to replace a huge resistor that you could not easily reach and was imposable to get a soldering gun down to. So I repositioned that so it was out in the open and easy to access so keep that in mind when laying out parts. D2, D3, D4 and D5 are going to save your meters but I am wondering what C9 and C18 are for? Remember if R6 or R15 open they will have 5Kv across them and not be real happy about it. R16 and R11 may be toast when R6 or R15 open too. Don’t get me wrong, I am not saying don’t do it this way because what your doing is standard in almost every vacuum tube broadcast transmitter just trying to point out that you want to have easy access to all that stuff so if in the event something in the tank fails or if you have a HV interlock and decide to test it or somehow forget that the HV is on and it does its job that’s the type of damage you can expect to see. Also why tubes instead of diode stacks?   

[W7TFO]

Also why tubes instead of diode stacks?   

'Cause guys like us are sick of solid state crap.

"We have MV rectifiers and are not afraid to abuse them!" Quote PJK.

73DG

[K1JJ]

A few tips about using remote-located blowers. Getting a quiet shack can certainly be a challenge sometimes:

For remote blowers, I have found that the ducting material needs to have a smooth inside, otherwise ribbing will cause air turbulence producing more back pressure, more air noise and less air flow. Thus, the blower needs to run faster = more noise, etc.

I once tried using 4" diameter PVC pipe as the ducting. The concept sounded good on paper, smooth inside, etc. The run was about seven feet from the blower mounted outside the wall to the tube chassis. But alas, the blower sounds were amplified like a trumpet!  It was like the blower was in the room, but even louder.  The PVC pipe had no sound absorbing qualities. The solution was to get some flexible fiberglass ducting on the internet that had a smooth interior. This solved all noise problems. IE, we need a ducting made of material that does not conduct noise well.

I also tried an outside-the-house blower that pushed air in. The downside was the weather moisture caused rusting of the tube and chassis components. In the winter it was murder when pushing in the cold air.  So, mounting a blower on the outside wall in a warm room is better.

Last, be sure to mount the blower on rubber or styro insulation, etc., without screws making a direct connection to anything that can transfer vibration.

Another experiment was to use acoustical panels on the walls and ceilings to reduce reflections.  A friend tried this and it was a bust. Small return for big effort.

I spent a lot of time making acoustical measurements with a meter and then adjusting all of these parameters. When using a big blower, eventually we can find a way to get it to run quiet.  For BIG rigs, sometimes the only way is to run the entire rig in another room remote.

The pleasure of operating in a quiet or almost quiet room cannot be emphasized enough.

T

[Opcom]

I've got to get this blower spun up and see just how much noise it makes. I don't 'have' to use it, but if I do, then it leaves open the possibility of using a larger amplifier tube in the future.

The MV tubes are nice, about the largest commonly available size, and good to look at. Since the 3CX3000A7 does not glow, the MV rectifiers will serve that function.

That is one reason I want the amplifier to be in the room, so it can be seen. I don't always get what I want but it's worth trying for.

[KL7OF]

flex connection between the fan and the ducting can help eliminate noise transfer .

[N2DTS]

Its really nice having a silent transmitter in a quiet room.

One idea to remember is that they make in duct fans as booster fans for heating systems.
You can get a cheap plastic blade four inch one at home despot and better metal blade ones on line.
They are quiet and move a good amount of air.

[Opcom]

As it turns out this is the only 3600RPM blower here. The others are 1720, etc. Almost every blower that is not a 3000+ RPM unit has not made the pressure needed to do this job, but I have only 5-6 blowers on hand.

I got this monster fired up. The schematic posted using an 80uF cap to start it worked well. It took about 15 seconds to get up to speed. It was run off a 120->240V 1KVA transformer for this experiment, and that may have limited the juice to some degree. When running the amp draw on the 120V side was 9A. This would be 4.5A on the 240V side, which is close to 4.4A the motor's rating. I need to measure the amps on each of the three wires on the motor as they should be balanced as well as possible consistent with the fan actually running.

It is quite noisy but I have hopes of noise abatement. I will work with this some more and make sure it is usable, does not overheat, etc.

[KA3EKH]

Another thought about the design, what’s the insulation value of your filament transformer L2? I am use to broadcast service where the transmitter is on all the time but in Ham service the transmitter is almost never on compared to the amount of time spent in standby. On the broadcast transmitter that I have running on 160 what I do is use the key line to control the plate contactor so the HV is off until you switch the transmitter into ON, but looking at your design it appears that you have your HV set so its ON and are using X64 and R18 to cut off the tube when not transmitting or in standby. This is going to crank the cathode filament voltage way up and if L2 is not built with the right amount of insulation bad things may happen, also C5 will need to be able to withstand the high voltages that will appear on it at that time.