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"New" method of fabricating a better chimney
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pentalab
Since Eimac never made a chimney for either a 3CX-3000A7 or a
3CX-6000A7 [or the socket] several after market chimneys have appeared. I purchased the one for the 6000A7. It was solid 1/4" thick teflon... straight up and down, no flanges.... and it's weight held it to the chassis. 6.130" ID 6.630" OD We found that this restricted the airflow up from the chassis too much. [both the ceramic 'stem' on the 3000/6000 are identical.. and much smaller diam than a YC-156 or a 10,000A7. ] For an experiment, I remember W7IUV had fabricated a fiberglass box around his YC-156.. for a chimney. We tried the same trick... except the vertical sidewalls were made from wood... about 9" square... top was also made from wood.... and the original chimney was placed in a groove.. on top of this wooden affair. Now we could increase the hole sizes on the chassis. The result was a huge improvement! Intead of the original 205 cfm... we are now getting an easy 320 cfm [using a Dayton 5C508 dual speed, capacitor start blower]. On the next chimney... we will toss the after market straight up and down chimney... and just increase the vertical sides of the box... and use a solid teflon top lid.. with a 6.130" hole in it. This technique can be used on any metal tube. The after market chimney's for the 3000A7 [4.130" ID] restrict the air too much as well. On one 3000A7 project... I used a SK- 306.. designed for a 4CX-5000A7.. which is a bit too big a diam at the top.... so we filled the gap.. by wrapping a few layers of silicone rubber around the tube.. held in place by a SS hose clamp... worked good. ... since the SK-306 chimney has a flared out base. Eimac specs the 6000A7 for 205 cfm of air. [based on a 50 deg C /121 deg F inlet air temp.] With 320+ cfm... and an inlet air temp of 25 deg C..... we calculated the anode diss is now an easy 8500+ Watts ! Talk about the sleeper of the year. This tube is real easy to increase it's stock anode dissipation. The secret is the small diam ceramic 'stem',makes for larger fins underneath... compared to a say 5000A7/YC-156..... which has a huge diam 'stem'... and a smaller anode cooler. The Dayton 5C508 blower is a dual speed 1100 rpm /1450 rpm unit. Comes with a single oil filled start cap. The over temp protected motor is partially embedded in one end. It draws intake air from both ends. With no back pressure... in free air, it's 765 cfm on high speed..... and down to 320 cfm @ .9" water pressure. They installed clip weights to some of the impellor blades.... so it's perfectly balanced from the factory... like balancing a car wheel. Later..... Jim VE7RF |
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Peter Voelpel
Hi Jim,
I use heatresistant glass cylinders I get made locally and also use round teflon covers as you, thats works very well. All my blowers are made by EBM. I do not like to boost a tubes rating, I rather prefer then to use a bigger one. I prefer that my GG amps cannot run in too high dissipation at full drive. They should have no problem when the antenna gets lost... 73 Peter --- In ham_amplifiers@..., "pentalab" <jim.thomson@...> wrote: For an experiment, I remember W7IUV had fabricated a >fiberglass |
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craxd
Peter & Jim,
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I started using a thick fish paper and paper tubing like that used for RF coils. You can buy it in larger diameters. I tried some with some 4CX250B's just to see how it worked and it was ok. The tubing is made from an electrical insulation type paper. The fish paper sheets is the blue or gray type, and about 1/6" thick. It's the same stuff you can make transformer bobins with. The tubes don't get hot enough to do anything to the paper, including the larger tubes if the air is flowing. The paper tubing is made by Precision Paper Tube. They supply the electrical/electronics industry. Oceanstate Electronics has the fish paper. A Google search will quickly find both. Best, Will --- In ham_amplifiers@..., "Peter Voelpel" <df3kv@...> wrote:
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Tony King - W4ZT
The straight up and down chimney will work pretty well if the flange is sub mounted below the chassis so air has a better path up through the anode. That's the plan here for the YC-156/179.
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73, Tony W4ZT pentalab wrote: Since Eimac never made a chimney for either a 3CX-3000A7 or a 3CX-6000A7 [or the socket] several after market chimneys have appeared. I purchased the one for the 6000A7. It was solid 1/4" thick teflon... straight up and down, no flanges.... and it's weight held it to the chassis. 6.130" ID 6.630" OD We found that this restricted the airflow up from the chassis too much. [both the ceramic 'stem' on the 3000/6000 are identical.. and much smaller diam than a YC-156 or a 10,000A7. ] For an experiment, I remember W7IUV had fabricated a fiberglass box around his YC-156.. for a chimney. We tried the same trick... except the vertical sidewalls were made from wood... about 9" square... top was also made from wood.... and the original chimney was placed in a groove.. on top of this wooden affair. Now we could increase the hole sizes on the chassis. The result was a huge improvement! Intead of the original 205 cfm... we are now getting an easy 320 cfm [using a Dayton 5C508 dual speed, capacitor start blower]. |
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pentalab
--- In ham_amplifiers@..., "Peter Voelpel" <df3kv@...>
wrote: use round teflon covers as you, thats works very well.a bigger one.full drive. They should have no problem when the antenna gets lost...### Partially agreed. ..BUT the 3CX-6000A7 is rated at 3.5 A of plate current CCS. [7 kv under load] . ## as is.... with 2.5 A of plate current @ aprx 6900 V under load.... DC input is 17.25 kw....... output is 11.5 kw. Anode diss is 5.75 kw. At 6kw of anode diss.... lower anode seal [ where the anode meets the ceramic] will be 225 Deg C ! ### I don't like running tubes anywhere near their max anode diss. The saving grace here is ssb/cw............ the duty cycle is WAY down. Plus Eimac's air flow specs are based on a 50 deg C [121 deg F] intake temp... which it's not. ### The point here is.... one would HAVE to increase the anode diss with more airflow.... in order to operate with 3 - 3.5 A of plate current. ### Eimac also makes an industrial heater tube.... 3CX-10,000D with a real small anode... 6.4" diam. I phoned em up..... they just blew more air through it to get the 10 kw anode diss ! ### also note the Eimac 3CX-10,000A7 and also the 3CX-15,000A7 have IDENTICAL physical dimensions in every regard. What's the diff ??? They just blow more air through the 15K... that's it. ### Both the 3CX-2500 and the 3CX-3000A7 have IDENTICAL dimensions/weights. BOTH are rated at 4000 watts of anode diss... CCS ! Eimac tells me the 2500 was origionally 2.5 kw anode diss.... then they upped the airflow....... ditto with the 3000A7. ### The 6000A7 is one of the easiset to cool [ and to increase the anode diss if needed/wanted] . Reason is.... the ceramic stem is real small diam compared to a YC-156.. 10K, 5K. With it's 6.125" OD cooler..... you end up with a HUGE fin area underneath. ## To really utilize this huge fin area underneath... it's gotta be able to breath right........... and that means the AREA of the holes /slots in the chassis should be at least the same or bigger, than the underneath fin AREA. And that means NO straight up/down chimneys can be used......... hence the 9" square box we used. ### The Eimac 10,000 chimney is a virtual straight up and down affair.... and chokes off the airflow from the chassis. ### When I see a 5 HP... 3 phase 208V blower motor for a pair of 3CX-15,000A7'S...... it makes me gag. ### Compare the pressure requirements of a YC-156 [or a 4CX- 5000] vs a 3CX-6000A7... you will get the idea. [compare em at the SAME 50 deg C inlet air temp] Jim VE7RF were frommade from wood... about 9" square... top was also made onwood.... and the original chimney was placed in a groove.. holetop of this wooden affair. Now we could increase the 205sizes on the chassis. Daytoncfm... we are now getting an easy 320 cfm [using a 5C508 dual speed, capacitor start blower]. |
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