Print

[VE7RF]

10 kw CCS on 6M..using the 3CX-6000A7...Part 9.

Ok, here the hb plate choke is wound on a solid teflon rod.  It sits dead center on top of the square copper plate. Copper plate bonds all 4 x bypass caps....and is also where the 6 kv will terminate.  The square copper plate heatsinks the tops of the 4 x caps.  The chassis  heatsinks the bottoms of the same 4 x caps.

The termination for the top of the winding....will be wired straight across  to the outer circumference of the anode.  The  .515" thick walled  teflon chimney as sold by ICA manufacturing, is 6" tall.   Scott had him cut it down a bit, down to 5" tall.    Done that way, the top portion of the anode is then exposed, and a copper strap will be wrapped around the entire circumference of the anode.

This strap will be used to terminate the B+.  It will also be used to terminate the plate block cap assy.

https://www.youtube.com/watch?v=TdANa0lVpeI

[VE3WGO]

I have seen various ways to connect to the anode of these ceramic tubes over the years.  Sometimes just a strap around the outer perimeter of the anode cooler fins with a single connection to the HV and output network, sometimes a connection to the top cap, and other times with more than one connection to parallel resonators.

Some builders worry about lack of symmetry on a single-point connection to the outer fin area causing unbalanced current maxima at certain points around the anode fins.  They might prefer a connection to the top cap area, while minimizing the connecting strap's blockage of air flow.

But I would expect that since the anode is a high impedance node, it's not a high current point therefore this is not a real concern.  Besides, there are so many parallel current paths through all the fins that the current must surely be shared pretty well among them.

Your thoughts?

73, Ed

[VE7RF]

I have seen various ways to connect to the anode of these ceramic tubes over the years.  Sometimes just a strap around the outer perimeter of the anode cooler fins with a single connection to the HV and output network, sometimes a connection to the top cap, and other times with more than one connection to parallel resonators.

Some builders worry about lack of symmetry on a single-point connection to the outer fin area causing unbalanced current maxima at certain points around the anode fins.  They might prefer a connection to the top cap area, while minimizing the connecting strap's blockage of air flow.

But I would expect that since the anode is a high impedance node, it's not a high current point therefore this is not a real concern.  Besides, there are so many parallel current paths through all the fins that the current must surely be shared pretty well among them.

Your thoughts?

73, Ed

Oh, it's a high current point alright.  All that current that flows from anode to grid is directly in parallel with C1 tune cap. Problem is, the plate block cap assy is in series with both the hot side of the anode to grid C..and also the C1 hot side to chassis C.

As long as the strap is oriented vertical, so it does not impede airflow, it can be attached to the center of of the anode... but it's a wasted effort really.
This is no place to use a SS hose clamp around the anode either.   SS + RF is bad news...and will  turn black.

Typ, a copper strap is run around the circumference of the anode, with a slight gap, where both ends  bend 90 degs. Then it can be pinched tight, with a brass machine screw, and more brass hardware, flat washers etc.

B+  connection is tucked underneath  the strap, over to one side.    The actual RF connection is done the same way, but 30-90 degs  further along the  circumference of the  19.25" copper strap.   (tube is 6.125" in diam).

Those..'fins'   at the top and bottom of the anode are actually...'struts'  and are used to hold the huge cylinder  in place...that's it.   The actual fins are between the upper and lower struts..and are folded back on themselves, (just a bit, like 1/4"),  when they reach the inside of the cylinder.  If you stand the tube vertical, on a white sheet of paper, then shine a light onto the paper, then view from above, you will see that all the actual fins are no thicker than a razor blade.

In this case, with this 6m amp (and HF versions as well) the RF current is all flowing from the center anode..via the upper struts, over a narrow circumference...to the 19.25" copper strap. 

The tank circuit is a one off deal.  It uses 2 x inductors...with one of em between the anode and C1 tune cap.  It can be located either between anode and input to block cap assy.... OR between output of block cap assy..and  hot side of the C1 tune cap.  2nd coil goes between the C1 + C2 vac caps.

The anode to grid C + the 1st coil form a step down L network, which steps the plate load Z down to a much lower value...low enough that we can now design a PI network with a normal Q.  Without the 1st coil installed, the 43 pf of anode to grid C makes up 99% of the C1 tune cap, and the C1 tune cap has it's own min C value.   End result of that mess is a coil value between the tune and load caps that is low enough, so the PI net can be resonated....which results in an extremely high loaded Q...with extremely high current flowing through the coil, which then runs hot, cooks the caps on either side..and ends up also being narrow banded...= frequent re-tuning, when qsy'ing . The coil would have to then be oversized to handle the current, but same uh.

 (tube has 24.5 pf between anode + grid... which rises to 43 pf when plugged into the socket / grid ring finger stock. The extra 18.5 pf comes from the lower fins to the chassis below). Then add in any stray C from the upper RF deck rear + sidewalls..to the anode.  Hence the 2.5" spacing between the anode and rear wall..and also 2.5" spacing between anode and side wall..... since the tube is mounted in the back left corner.

We use the 2 x coil trick using the same series of GG triodes, with 80-10m amps, 160-10m amps, 160-15m amps, etc. I used the same trick to get a better, lower Q on 15m, on my own 160-15m hb 3x3 tube amp.  One caveat though. It can't be used on tubes that require a parasitic suppressor. The 8877, 3x3/6/10/15/20, and also YC-156/172 don't require a suppressor, so non issue.  The technique won't work on 811/572B / 3-400Z / 3-500Z  etc.

[KD6VXI]

Not sure I buy the whole "struts" on the anode chamber.

Cut them off.  Insert the tube in the socket.  They still work.

The 4CX250B all use 'struts'.  Except the one that is BeO coupled to a heat sink (sb230, etc).  So that doesn't wash either.  There are other tubes that are cooled the same way.

The fins are there for an interface from the anode to the air flow.  And blowing as much air as fast as you can through them isn't the best way to cool a tube either.  There is thermionic efficiency at play.

--Shane
WP2ASS / ex KD6VXI

[VE7RF]

Not sure I buy the whole "struts" on the anode chamber.

Cut them off.  Insert the tube in the socket.  They still work.

The 4CX250B all use 'struts'.  Except the one that is BeO coupled to a heat sink (sb230, etc).  So that doesn't wash either.  There are other tubes that are cooled the same way.

The fins are there for an interface from the anode to the air flow.  And blowing as much air as fast as you can through them isn't the best way to cool a tube either.  There is thermionic efficiency at play.

--Shane
WP2ASS / ex KD6VXI

Cut the top + bottom  struts off (at the inside of the cylinder)..and the entire cylinder falls right off.  At least on Russian 3x3's....and also Eimac YC-243's (socketless 3x6)....and probably the rest of the bigger tubes.    I just distinguish between the struts (which are thick)   vs the actual fins, which are no thicker than a razor blade. They are razor thin, and way more of em vs struts, since they (fins)  converge in the middle, at the anode.  At the outer periphery of each fin, it does a 90 deg arced bend for a bit, then back on to itself for a bit.  That arced bend doesn't even touch the inside of the cylinder.   The top + bottom struts are there just to hold the cylinder in place...and the cylinders only function is to  maintain airflow past the fins.

More air = more anode dissipation.  But there is practical upper limit, where the required increase in airflow also requires  a huge increase in pressure.  Sure, you can stuff 500 cfm through a keyhole, but the required pressure to do it is over the top.

Then there is the 3x6 tube, which is unique, in that it has a small diameter  ceramic ..'stem'  ( identical diam as a 3x3). The 'stem' on the 3x3, and 3x6 is one helluva lot smaller diam vs all the bigger tubes like the 3x10/15/20..and also the 4x5/10/15/20   and  YC-156/172 tubes..that all require huge pressure. The 3x6, with it's 6.125" OD anode cooler and small diameter ceramic stem results in a huge under fin area, and easy to cool..and low back pressure requirements. 

The 3x3 requires 67 cfm @ 1.2".    The 3x6 / YC-243 only requires 205 cfm @ just  .4".  The 3x6 / YC-243 is a prime candidate to blow more air through.  However, a 50% increase in CFM  only results in a 20% increase in anode dissipation.
And a 50% increase in CFM means  205 x 1.5 =  307.5 cfm.  Here's the catch. The required pressure increases to the square of the new / old CFM ratio.   1.5 x 1.5 = 2.25.   New pressure is now  2.25 X .4 = .9" 
 
307.5 cfm @ .9" is easily obtainable, and several readily available blowers, including several from Dayton, and also ebm-papst  ,ad also Emerson, and also Kooltronics will  do the job.   Ok, now the 3x6 has it's CCS anode diss increased to 6000 x 1.2 (20%) =  7200 watts.  For the 3x3 and  3x6 tubes, the above specs are based on 40 deg C intake air temps (104 deg F).  Well it's only 20-25 C (68-77 F) in my basement, so when the maths are worked out, the actual cfm required is a lot less for  cooler intake air temps. In the above case, with 50% increased airflow AND cooler intake air temps, the actual CCS anode diss increases to 8 kw.   That's not bad for a readily available blower being used... (and inexpensive if a Dayton 5C508 / 1TDT8 is used. The 1TDT8 is the new version, and uses start and run caps, and also has ball bearings. Both old + new versions are 2 x speed units...and the lower speed is more than ample on either version to provide for 50% increased airflow on a 3x6 / YC-243.   

Let's say you want to increase cfm by another 50%. (= 461.25 cfm). The new required pressure then becomes   2.25 X .9 = 2.025".   461.25 cfm @ 2.025" is doable..and blowers are available.  2 x blowers in parallel can also be used.  In this case, each blower  would have to be rated at (461.5 / 2)  =  230.75 cfm @  2.025".  (on that 4x15 amp on Scott's U tube channel, 3 x identical ebm-papst blower's were used).   With the additional  50% airflow, CCS anode diss increases by another 20% or  7.2 kw X 1.2 = 8.640 kw...(and still more if room temps are reasonable).

Want more, go another 50%, and now it's gone nuts at  691.875 cfm @ 4.55625" . Diss is now 10.4 kw...and more if room temps are reasonable.  I gotta draw the line somewhere, and the 1st  50% increase is ample for this application.

You can easily do  the same calcs on other tubes, and you will see where the diminishing returns are.   High pressure blowers don't come cheap, and are typ hp rated...and suck a lot of current.   There is big, then there is too big.  That next 3db much above 10-15 kw becomes  impractical... esp when the typ home only has 200 amp service.  The logistical  nightmare of coax, flexible coax, connectors, CM chokes, ants etc, etc, becomes a complicated mess.   

[KM4AH]

When I shoot my YC156A anode with a laser temp sensor I get about 105 F. Hottest I have seen it was 115 F.

What would normal or good be ?

[VE7RF]

When I shoot my YC156A anode with a laser temp sensor I get about 105 F. Hottest I have seen it was 115 F.

What would normal or good be ?

Those IR point + shoot thermometers, like my fluke 62 (the laser is just a pointing aid)  measure surface temp, not air temp.   Eimac sez  max seal temp, where the anode meets the ceramic, is 250 degs C. Their cooling specs are for 225 deg C. 

105 F... it's not even doing anything.   Is that with just the heater on, tube in cutoff, and no drive applied ?  If it's just 1.5 to 2 kw on ssb, you sure don't have a heat issue.  What is the temp, with 1.5 kw cxr ?

[W9IQ]

One should keep in mind that the CFM and static pressure numbers for a tube are under very specific conditions and should be considered "ideal" - not the design parameters.

A reduction in air density beyond the cooling specification reduces the cooling capacity since it isn't CFM that determines cooling but rather the mass of air being moved. Air density is largely a function of altitude in most designs (temperature and humidity to a lesser extent). Most tube datasheets are based on sea level air densities. A moderate altitude of 2000 feet results in reducing the air mass and therefore cooling capacity to 83% that of sea level. Then consider that Denver is over 5000 feet ASL.

An increase in frequency of operation beyond the cooling specification generally requires increased CFM due to increased tube dissipation.

An increase in ambient temperature beyond the cooling specification generally requires increased CFM since the ΔT may push the tube beyond its ultimate temperature limitation. Higher power / higher duty cycle amps in small rooms may additionally require mechanical cooling due to the otherwise closed loop thermal condition causing the ambient to exceed the design parameter.

The air filter, ducting, chimney, cabinet, mounting conditions, neglected air filters, etc. all increase the system impedance. This means that the fan/blower must deliver the required CFM at an increased static pressure from that shown on the tube datasheet.

- Glenn W9IQ

[VE7RF]

One should keep in mind that the CFM and static pressure numbers for a tube are under very specific conditions and should be considered "ideal" - not the design parameters.

A reduction in air density beyond the cooling specification reduces the cooling capacity since it isn't CFM that determines cooling but rather the mass of air being moved. Air density is largely a function of altitude in most designs (temperature and humidity to a lesser extent). Most tube datasheets are based on sea level air densities. A moderate altitude of 2000 feet results in reducing the air mass and therefore cooling capacity to 83% that of sea level. Then consider that Denver is over 5000 feet ASL.

An increase in frequency of operation beyond the cooling specification generally requires increased CFM due to increased tube dissipation.

An increase in ambient temperature beyond the cooling specification generally requires increased CFM since the ΔT may push the tube beyond its ultimate temperature limitation. Higher power / higher duty cycle amps in small rooms may additionally require mechanical cooling due to the otherwise closed loop thermal condition causing the ambient to exceed the design parameter.

The air filter, ducting, chimney, cabinet, mounting conditions, neglected air filters, etc. all increase the system impedance. This means that the fan/blower must deliver the required CFM at an increased static pressure from that shown on the tube datasheet.

- Glenn W9IQ

Ur correct.   But most amps don't include air filters.  I include then on my hb amps,  and size them so their surface area is far greater than the  intake surface area of the blower.  Lately, I have been using 3M filters, since nothing get's past them, and they have low pressure drop across a NEW filter...provided they are installed correctly.  Currently, I'm trying to come up with a  filter design, for the intake of my L4B's..which have been modified and now use the ebm-papst blower from the AL-1200/1500/82 ameritron amps.

In Denver, at 5000 ft, both the cfm AND the pressure both have to be increased by 20%   vs sea level.  The kicker is, blowers are all sea level rated @ 25 deg C !   You have to go through a series of math calcs to determine what sea level rated blower will do the job at higher elevations....and also  higher ambient temps...if ambient temps are > 25 deg C. 

Cooling specs are all over the map.   Most will provide specs for sea level...and also 5/10k elevation.  Some specs are for 40 deg C ambient intake air..and most are for 50 deg C.  Some are as low as 25 deg C.  Some tubes like the YC-156 provide specs for 25/35/50 deg C in take air.   

I factor all of this into the final design.  I managed to buy a pair of ebm -papst blowers that are the EC type (electronic commutator). They run on 115 vac 50/60 hz  and put out 70 cfm @ 1.2" pressure...and only draw .42 amp. One is ample for my 3x3 amp.  With a 10k pot in the mix, the speed can be varied from a max of 2810 rpm ....down to just  1400 rpm.  At 1400 rpm, it only draws .05 amp....which is ample for extended RX, with tube heater on.

The blower comes with a built in 10 vdc supply...and for max speed, it's wired directly to the PWM input of the blower. With the 10 k pot installed, the vdc can be varied from 0 to 10 vdc...and fed to the PWM input... resulting in a 1400-2810 rpm range.   I'm trying to minimize blower power, and these EC types work superb.   Also tried experimenting with lower cfm on RX...and faster on TX...... with a 6-10 second delay between when VOX drops out....and blower drops to the (dialed in) lower speed.

[KD6VXI]

Not sure I buy the whole "struts" on the anode chamber.

Cut them off.  Insert the tube in the socket.  They still work.

The 4CX250B all use 'struts'.  Except the one that is BeO coupled to a heat sink (sb230, etc).  So that doesn't wash either.  There are other tubes that are cooled the same way.

The fins are there for an interface from the anode to the air flow.  And blowing as much air as fast as you can through them isn't the best way to cool a tube either.  There is thermionic efficiency at play.

--Shane
WP2ASS / ex KD6VXI

Cut the top + bottom  struts off (at the inside of the cylinder)..and the entire cylinder falls right off.  At least on Russian 3x3's....and also Eimac YC-243's (socketless 3x6)....and probably the rest of the bigger tubes.    I just distinguish between the struts (which are thick)   vs the actual fins, which are no thicker than a razor blade. They are razor thin, and way more of em vs struts, since they (fins)  converge in the middle, at the anode.  At the outer periphery of each fin, it does a 90 deg arced bend for a bit, then back on to itself for a bit.  That arced bend doesn't even touch the inside of the cylinder.   The top + bottom struts are there just to hold the cylinder in place...and the cylinders only function is to  maintain airflow past the fins.

More air = more anode dissipation.  But there is practical upper limit, where the required increase in airflow also requires  a huge increase in pressure.  Sure, you can stuff 500 cfm through a keyhole, but the required pressure to do it is over the top.

Then there is the 3x6 tube, which is unique, in that it has a small diameter  ceramic ..'stem'  ( identical diam as a 3x3). The 'stem' on the 3x3, and 3x6 is one helluva lot smaller diam vs all the bigger tubes like the 3x10/15/20..and also the 4x5/10/15/20   and  YC-156/172 tubes..that all require huge pressure. The 3x6, with it's 6.125" OD anode cooler and small diameter ceramic stem results in a huge under fin area, and easy to cool..and low back pressure requirements. 

The 3x3 requires 67 cfm @ 1.2".    The 3x6 / YC-243 only requires 205 cfm @ just  .4".  The 3x6 / YC-243 is a prime candidate to blow more air through.  However, a 50% increase in CFM  only results in a 20% increase in anode dissipation.
And a 50% increase in CFM means  205 x 1.5 =  307.5 cfm.  Here's the catch. The required pressure increases to the square of the new / old CFM ratio.   1.5 x 1.5 = 2.25.   New pressure is now  2.25 X .4 = .9" 
 
307.5 cfm @ .9" is easily obtainable, and several readily available blowers, including several from Dayton, and also ebm-papst  ,ad also Emerson, and also Kooltronics will  do the job.   Ok, now the 3x6 has it's CCS anode diss increased to 6000 x 1.2 (20%) =  7200 watts.  For the 3x3 and  3x6 tubes, the above specs are based on 40 deg C intake air temps (104 deg F).  Well it's only 20-25 C (68-77 F) in my basement, so when the maths are worked out, the actual cfm required is a lot less for  cooler intake air temps. In the above case, with 50% increased airflow AND cooler intake air temps, the actual CCS anode diss increases to 8 kw.   That's not bad for a readily available blower being used... (and inexpensive if a Dayton 5C508 / 1TDT8 is used. The 1TDT8 is the new version, and uses start and run caps, and also has ball bearings. Both old + new versions are 2 x speed units...and the lower speed is more than ample on either version to provide for 50% increased airflow on a 3x6 / YC-243.   

Let's say you want to increase cfm by another 50%. (= 461.25 cfm). The new required pressure then becomes   2.25 X .9 = 2.025".   461.25 cfm @ 2.025" is doable..and blowers are available.  2 x blowers in parallel can also be used.  In this case, each blower  would have to be rated at (461.5 / 2)  =  230.75 cfm @  2.025".  (on that 4x15 amp on Scott's U tube channel, 3 x identical ebm-papst blower's were used).   With the additional  50% airflow, CCS anode diss increases by another 20% or  7.2 kw X 1.2 = 8.640 kw...(and still more if room temps are reasonable).

Want more, go another 50%, and now it's gone nuts at  691.875 cfm @ 4.55625" . Diss is now 10.4 kw...and more if room temps are reasonable.  I gotta draw the line somewhere, and the 1st  50% increase is ample for this application.

You can easily do  the same calcs on other tubes, and you will see where the diminishing returns are.   High pressure blowers don't come cheap, and are typ hp rated...and suck a lot of current.   There is big, then there is too big.  That next 3db much above 10-15 kw becomes  impractical... esp when the typ home only has 200 amp service.  The logistical  nightmare of coax, flexible coax, connectors, CM chokes, ants etc, etc, becomes a complicated mess.

I was confusing your term struts to mean the actual fins.  Lost in translation from canadian to american LOL


As to just stuffing more and more air through, this hits a limit.  Just like cooling an engine, the absolute fastest water pump doesn't do it.  Just like cooling an engine when they use a T-Stat to stop the water, transfer heat into the water from the block, then circulate to the radiator.  Lather, rinse and repeat.

--Shane
WP2ASS / ex KD6VXI

[KM4AH]

When I shoot my YC156A anode with a laser temp sensor I get about 105 F. Hottest I have seen it was 115 F.

What would normal or good be ?

Those IR point + shoot thermometers, like my fluke 62 (the laser is just a pointing aid)  measure surface temp, not air temp.   Eimac sez  max seal temp, where the anode meets the ceramic, is 250 degs C. Their cooling specs are for 225 deg C. 

105 F... it's not even doing anything.   Is that with just the heater on, tube in cutoff, and no drive applied ?  If it's just 1.5 to 2 kw on ssb, you sure don't have a heat issue.  What is the temp, with 1.5 kw cxr ?

Actually that is after a typical SSB rag chew, maybe 30 minutes or whatever.

[VE7RF]

When I shoot my YC156A anode with a laser temp sensor I get about 105 F. Hottest I have seen it was 115 F.

What would normal or good be ?

Those IR point + shoot thermometers, like my fluke 62 (the laser is just a pointing aid)  measure surface temp, not air temp.   Eimac sez  max seal temp, where the anode meets the ceramic, is 250 degs C. Their cooling specs are for 225 deg C. 

105 F... it's not even doing anything.   Is that with just the heater on, tube in cutoff, and no drive applied ?  If it's just 1.5 to 2 kw on ssb, you sure don't have a heat issue.  What is the temp, with 1.5 kw cxr ?

Actually that is after a typical SSB rag chew, maybe 30 minutes or whatever.

The fil is 15 V @ 15A = 225 watts CCS.   That 105F you are measuring, is just the fil..which is normal.

[VE7RF]

Not sure I buy the whole "struts" on the anode chamber.

Cut them off.  Insert the tube in the socket.  They still work.

The 4CX250B all use 'struts'.  Except the one that is BeO coupled to a heat sink (sb230, etc).  So that doesn't wash either.  There are other tubes that are cooled the same way.

The fins are there for an interface from the anode to the air flow.  And blowing as much air as fast as you can through them isn't the best way to cool a tube either.  There is thermionic efficiency at play.

--Shane
WP2ASS / ex KD6VXI

Cut the top + bottom  struts off (at the inside of the cylinder)..and the entire cylinder falls right off.  At least on Russian 3x3's....and also Eimac YC-243's (socketless 3x6)....and probably the rest of the bigger tubes.    I just distinguish between the struts (which are thick)   vs the actual fins, which are no thicker than a razor blade. They are razor thin, and way more of em vs struts, since they (fins)  converge in the middle, at the anode.  At the outer periphery of each fin, it does a 90 deg arced bend for a bit, then back on to itself for a bit.  That arced bend doesn't even touch the inside of the cylinder.   The top + bottom struts are there just to hold the cylinder in place...and the cylinders only function is to  maintain airflow past the fins.

More air = more anode dissipation.  But there is practical upper limit, where the required increase in airflow also requires  a huge increase in pressure.  Sure, you can stuff 500 cfm through a keyhole, but the required pressure to do it is over the top.

Then there is the 3x6 tube, which is unique, in that it has a small diameter  ceramic ..'stem'  ( identical diam as a 3x3). The 'stem' on the 3x3, and 3x6 is one helluva lot smaller diam vs all the bigger tubes like the 3x10/15/20..and also the 4x5/10/15/20   and  YC-156/172 tubes..that all require huge pressure. The 3x6, with it's 6.125" OD anode cooler and small diameter ceramic stem results in a huge under fin area, and easy to cool..and low back pressure requirements. 

The 3x3 requires 67 cfm @ 1.2".    The 3x6 / YC-243 only requires 205 cfm @ just  .4".  The 3x6 / YC-243 is a prime candidate to blow more air through.  However, a 50% increase in CFM  only results in a 20% increase in anode dissipation.
And a 50% increase in CFM means  205 x 1.5 =  307.5 cfm.  Here's the catch. The required pressure increases to the square of the new / old CFM ratio.   1.5 x 1.5 = 2.25.   New pressure is now  2.25 X .4 = .9" 
 
307.5 cfm @ .9" is easily obtainable, and several readily available blowers, including several from Dayton, and also ebm-papst  ,ad also Emerson, and also Kooltronics will  do the job.   Ok, now the 3x6 has it's CCS anode diss increased to 6000 x 1.2 (20%) =  7200 watts.  For the 3x3 and  3x6 tubes, the above specs are based on 40 deg C intake air temps (104 deg F).  Well it's only 20-25 C (68-77 F) in my basement, so when the maths are worked out, the actual cfm required is a lot less for  cooler intake air temps. In the above case, with 50% increased airflow AND cooler intake air temps, the actual CCS anode diss increases to 8 kw.   That's not bad for a readily available blower being used... (and inexpensive if a Dayton 5C508 / 1TDT8 is used. The 1TDT8 is the new version, and uses start and run caps, and also has ball bearings. Both old + new versions are 2 x speed units...and the lower speed is more than ample on either version to provide for 50% increased airflow on a 3x6 / YC-243.   

Let's say you want to increase cfm by another 50%. (= 461.25 cfm). The new required pressure then becomes   2.25 X .9 = 2.025".   461.25 cfm @ 2.025" is doable..and blowers are available.  2 x blowers in parallel can also be used.  In this case, each blower  would have to be rated at (461.5 / 2)  =  230.75 cfm @  2.025".  (on that 4x15 amp on Scott's U tube channel, 3 x identical ebm-papst blower's were used).   With the additional  50% airflow, CCS anode diss increases by another 20% or  7.2 kw X 1.2 = 8.640 kw...(and still more if room temps are reasonable).

Want more, go another 50%, and now it's gone nuts at  691.875 cfm @ 4.55625" . Diss is now 10.4 kw...and more if room temps are reasonable.  I gotta draw the line somewhere, and the 1st  50% increase is ample for this application.

You can easily do  the same calcs on other tubes, and you will see where the diminishing returns are.   High pressure blowers don't come cheap, and are typ hp rated...and suck a lot of current.   There is big, then there is too big.  That next 3db much above 10-15 kw becomes  impractical... esp when the typ home only has 200 amp service.  The logistical  nightmare of coax, flexible coax, connectors, CM chokes, ants etc, etc, becomes a complicated mess.

I was confusing your term struts to mean the actual fins.  Lost in translation from canadian to american LOL


As to just stuffing more and more air through, this hits a limit.  Just like cooling an engine, the absolute fastest water pump doesn't do it.  Just like cooling an engine when they use a T-Stat to stop the water, transfer heat into the water from the block, then circulate to the radiator.  Lather, rinse and repeat.

--Shane
WP2ASS / ex KD6VXI

The problem with the engine analogy is.... it's a closed loop.  Same thing happens with the small positive displacement blower on my 2010 mustang. The intercooler - degas bottle - pump - HE- back to the intercooler...is all one big loop. Increase the pump gpm, and  all you end up doing is increasing the loop speed...and spinning hot water around in the loop.

Ideally, you want fast water flow in the IC (to extract heat)..... and slow water flow through the 19" tall x 21" wide air cooled HE....( to dump the extracted heat)...  but you can't, cuz it's a closed loop.  Without a bigger HE, a bigger pump doesn't work.   Now if you instead had an endless supply of cool water, (like a swimming pool, or a lake / ocean)  a bigger pump will work...then dump the hot water.

With tubes, you can sorta depend on an endless supply of cooler intake air.... depending on ambient room temps, how big the room is... but you have to either dump the hot air back to the room, increasing the room's ambient temp.... or dump the hot air to the outside.  If dumped to the outside, you have to then draw an equal amount of outside air (makeup air) back into the room.

Depending on heat involved, outside air temps, room size etc, some AC might well be required.  At least AC is 300% eff, for extracting heat.    At 3.41  BTU's per watt, it's sorta a straightforward series of heat calculations.  If you are doing FM broadcast in AZ, or the middle east, and still using tubes, the worse case cooling scenario would have to be very carefully thought out.

[W9IQ]

In Denver, at 5000 ft, both the cfm AND the pressure both have to be increased by 20%   vs sea level.

So here is an interesting question for you, Jim. If the CFM must increase by 20% due to the decreased air density (mass/volume) then why does Eimac say the static pressure increases by only 20% when earlier you said that it should increase by the square of the ratio of the CFM which would result in a 44% increase in this case?

The kicker is, blowers are all sea level rated @ 25 deg C !   You have to go through a series of math calcs to determine what sea level rated blower will do the job at higher elevations....and also  higher ambient temps...if ambient temps are > 25 deg C.

Be careful here as you are double counting if you do that. If a blower manufacturer shows air and temperature derating curves, they are reworking the air density calculations from the supply side. If you have already done the calculations based on the load side (e.g. per the Eimac recommendation), you should not use their derated curves.

- Glenn W9IQ 

[W9IQ]

Be careful here as you are double counting if you do that. If a blower manufacturer shows air and temperature derating curves, they are reworking the air density calculations from the supply side. If you have already done the calculations based on the load side (e.g. per the Eimac recommendation), you should not use their derated curves.

I should amend this latter part as it is too broad as written. The fan altitude derating curves should be examined to determine if the CFM rating is being adjusted for the motor load performance at altitude or if it is an equivalent CFM at sea level curve. It is the latter that would result in double counting. Constant speed fans will deliver the same CFM but less cooling at altitude.

- Glenn W9IQ