3-500Z Infrared Radiation

[KD1SH]

   Yes indeed, it is one hell of a blower; it could probably supply the airflow requirements for a good sized commercial broadcast tube with ease.
   I plan to do just as you suggest - mount the blower inside a baffled wooden enclosure - but that beast won't be in the shack with me; it'll be mounted remotely down in the basement somewhere, with a long hose and rubber vibration dampers.
   Good idea about the Mylar. Or maybe just an aluminum tube of the appropriate ID, and since I'll have air to spare, maybe a circle of small holes to allow some airflow around it. The problem with my plate-choke concerns is that it's all purely conjecture at this point. I'm thinking that, in order to conserve space, those three tubes will be mounted just close enough together to allow for mounting the choke in the middle - allowing room of course for the chimneys - and thus the choke will have cherry-red anodes only inches away on three sides. Being shiny white, the exposed ceramic core probably won't absorb much energy, but the enameled copper windings might be a different story.
   Looking at pictures of the innards of an Ameritron AL-82, it seems they've mounted their plate choke behind a fiberglass panel, but they may have had other reasons for that. The Drake L7 has no such shield; the choke is pretty snug to the tubes. The Amp Supply LK-550 has its trio of 3-500's laid out pretty much identically to mine but with no chimneys, so they're even closer than I'm planning, and the choke is snuggled right there in the center of them- nearly touching the tube envelopes. Those amps are all primarily SSB amps, though, while mine is intended for AM at legal limit, meaning cherry-red plates at buzzardly duty cycles.
  

A couple of things. You have enough blower there for several amps.
Have you considered mounting it in a wooden insulated box with baffles and use a 2 inch hose to connect to your chassis
It will be much quieter and still easily supply the 0.08 inch of water head pressure at the sockets.

As far as keeping the RF choke cool, you may consider getting some metalized Mylar film and rolling it into a conical cylinder with the diameter being a bit larger at the bottom and mount it half an inch using small angle brackets above the chassis to allow airflow and you may also drill a few 1/4 inch holes around the choke so that some of the air in the pressurized chassis flows upward from below. Mylar film can handle up to 400 degrees.
Consider making your conical cylinder 2.5 diameter at the bottom and 2 inches at the top. You need only make this shield rise 3 inches above the chassis.
Mylar is an excellent heat insulator and the aluminum coating will reflect I’ve 90% of the radiant heat back. Ideally, more  conicity will reflect the heat more upward toward the top of the camber so if you have space, make the bottom 3 inches diameter.

[Jim, W5JO]

   I plan to do just as you suggest - mount the blower inside a baffled wooden enclosure - but that beast won't be in the shack with me; it'll be mounted remotely down in the basement somewhere, with a long hose and rubber vibration dampers.

Don't forget to put a very good filter on that blower intake.

[KD1SH]

Yes. Gradual decrease in the basement spider population; gradual increase in back-pressure at the amp, accompanied by a foul smell. Not cool.

   I plan to do just as you suggest - mount the blower inside a baffled wooden enclosure - but that beast won't be in the shack with me; it'll be mounted remotely down in the basement somewhere, with a long hose and rubber vibration dampers.

Don't forget to put a very good filter on that blower intake.

[Opcom]

Have you considered a mechanism to hold the chimneys in place against the blower pressure?

Also make sure the blower motor isn't overloaded due to not enough airflow through the wheel (stall).

[K9MB]

  Yes indeed, it is one hell of a blower; it could probably supply the airflow requirements for a good sized commercial broadcast tube with ease.
   I plan to do just as you suggest - mount the blower inside a baffled wooden enclosure - but that beast won't be in the shack with me; it'll be mounted remotely down in the basement somewhere, with a long hose and rubber vibration dampers.
   Good idea about the Mylar. Or maybe just an aluminum tube of the appropriate ID, and since I'll have air to spare, maybe a circle of small holes to allow some airflow around it. The problem with my plate-choke concerns is that it's all purely conjecture at this point. I'm thinking that, in order to conserve space, those three tubes will be mounted just close enough together to allow for mounting the choke in the middle - allowing room of course for the chimneys - and thus the choke will have cherry-red anodes only inches away on three sides. Being shiny white, the exposed ceramic core probably won't absorb much energy, but the enameled copper windings might be a different story.
   Looking at pictures of the innards of an Ameritron AL-82, it seems they've mounted their plate choke behind a fiberglass panel, but they may have had other reasons for that. The Drake L7 has no such shield; the choke is pretty snug to the tubes. The Amp Supply LK-550 has its trio of 3-500's laid out pretty much identically to mine but with no chimneys, so they're even closer than I'm planning, and the choke is snuggled right there in the center of them- nearly touching the tube envelopes. Those amps are all primarily SSB amps, though, while mine is intended for AM at legal limit, meaning cherry-red plates at buzzardly duty cycles.
  

A couple of things. You have enough blower there for several amps.
Have you considered mounting it in a wooden insulated box with baffles and use a 2 inch hose to connect to your chassis
It will be much quieter and still easily supply the 0.08 inch of water head pressure at the sockets.

As far as keeping the RF choke cool, you may consider getting some metalized Mylar film and rolling it into a conical cylinder with the diameter being a bit larger at the bottom and mount it half an inch using small angle brackets above the chassis to allow airflow and you may also drill a few 1/4 inch holes around the choke so that some of the air in the pressurized chassis flows upward from below. Mylar film can handle up to 400 degrees.
Consider making your conical cylinder 2.5 diameter at the bottom and 2 inches at the top. You need only make this shield rise 3 inches above the chassis.
Mylar is an excellent heat insulator and the aluminum coating will reflect I’ve 90% of the radiant heat back. Ideally, more  conicity will reflect the heat more upward toward the top of the camber so if you have space, make the bottom 3 inches diameter.

I considered suggesting thin flashing aluminum coiled but it has no insulating properties.
The Mylar is a very good heat insulator.
The aluminum metalized surface reflects more than 90 percent of the radiation that hits it.
Mylar is easy to roll onto a cone and pin so it stays together and then punch the holes for the angle brackets to support it.
You need to consider the effects of metal close to an open solenoid winding like the RF Choke because of the capacitive effects and the close proximity can affect the Q of the choke. By using a conical section, you minimize this affect. A good rule of thumb for enclosing inductors is to allow a minimum of the diameter of the solenoid on all sides.
That would require over 3 inches of space.
Another possibility is to make a skeleton heat shield that puts a flat aluminum plate between the chimney and the choke. Kind of like a wall that casts s shadow on the choke in the direction of each tube. It would be like a box with corners open .
The conical shape will deflect heat upward snd out of the system.
Add the airflow and you have a cool RF choke.
MB

[KD1SH]

  I've got some of the original Eimac chimney clips, but probably not enough for all three chimneys, though I should be able to kludge up some of my own based on the originals.
  I will probably wind up using some sort of diverter valve, or waste gate, to dump excess airflow, since I will certainly wind up with vastly more than I need, and there's probably a flattening of the cooling efficiency curve at some point. I will probably settle for something like 150% or 200% of Eimac's minimum. That's just for comfort, really, since Eimac's airflow specs were calculated to allow for maximum rated plate dissipation, and I don't intend to exceed that.
  I'm thinking that I might even - inspired by this latest heatwave here in the Northeast - provide for an air discharge hose to exhaust the heated air back into the basement rather than here in the shack. The basement tends to run a good deal cooler than up here. It'll be quieter, too.

Have you considered a mechanism to hold the chimneys in place against the blower pressure?

Also make sure the blower motor isn't overloaded due to not enough airflow through the wheel (stall).

[K8DI]

Coming in late here, but have you considered a hollow/tube form for the plate choke, mounted to the chassis with a hole under it, so the same pressurized chassis air that blows through the sockets blows up the center of the choke, cooling it from the inside?

Ed

[K9MB]

Coming in late here, but have you considered a hollow/tube form for the plate choke, mounted to the chassis with a hole under it, so the same pressurized chassis air that blows through the sockets blows up the center of the choke, cooling it from the inside?

Ed

I see no reason it would not work and he has tons of air. Nice simple solution.

Edit:
The only downside I can see, upon reflection is that the focus has been on limiting the amount of heat producing radiation striking the choke as well as removing enough heat to prevent damage to the coil. Your solution will eliminate any heat that builds up on the hollow tube, but the heat gradient from winding to form and through the form might be long, given the liklihood that it will be a poor comductie of heat and the coil will still be hot. I still believe that a hollow shield around the choke that reflects and insulates is best. 73, MB

[W4DNR]

[quote author=KD1SH
if I were sitting on a skateboard and holding this thing, it would send me zooming around my shop. Sounds like fun, actually; if I had more room in my shop I might just plug in a long extension cord and try that
[/quote]


Do you charge admission ?   W4DNR

[w8khk]

[quote author=KD1SH
if I were sitting on a skateboard and holding this thing, it would send me zooming around my shop. Sounds like fun, actually; if I had more room in my shop I might just plug in a long extension cord and try that

Do you charge admission ?   W4DNR


When not decommissioning bounce-houses, Bill puts on quite a show with his airboat skateboard.  He has a very long extension cord.  It is exciting, and can potentially put undue stress on the ticker.  Don, you may have second thoughts about attending, especially when exhibiting that "Do Not Resuscitate" placard.

[KD1SH]

My wife would probably pay people to come and watch. But, like they say, people who attend such events probably just want to see a ham crash.

[quote author=KD1SH
if I were sitting on a skateboard and holding this thing, it would send me zooming around my shop. Sounds like fun, actually; if I had more room in my shop I might just plug in a long extension cord and try that

Do you charge admission ?   W4DNR
[/quote]