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Author Topic: 3-500 tube chimneys  (Read 3344 times)
K9FON
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« on: September 17, 2008, 06:09:40 PM »

Why do some amps (like the Drake L4B) use tube chimneys and some like my Swan MKII dont?
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N3JBH
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« Reply #1 on: September 18, 2008, 06:36:33 AM »

It is all about the cooling system... The drake has air forced up from the bottom of the tube socket colloing both the tube and the tubes base. The chimney directs the air up  over and around the tube,

The Swan  has air blown across the tube there for having a chimney would not let the air get to the tubes
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AD4U
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« Reply #2 on: September 18, 2008, 07:21:45 AM »

There is also the issue of cost.  It costs much less ($10.00 in OEM lots?) to purchase and install a 5 inch plastic fan to blow across the two tubes than it costs to buy two EIMAC chimneys and a blower with suitable back pressure specs and CFM to pressurize the chassis ($100.00 in OEM lots?).

This is one reason why amps with fans blowing across the tubes generally cost less lwhen new than amps with chimneys and a pressurized chassis.

Some will disagree, but IMO the pressurized chassis and chimney system cools the tubes and especially the tube pin seals much better than a fan blowing across the tubes.  If not, why would EIMAC make chimneys?

Dick  AD4U
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WD4HXG
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« Reply #3 on: September 18, 2008, 11:04:46 AM »

Eimac designed their products to be used in commercial service by end users who demanded high reliability.

If you look at the Eimac booklet on "The Care and Feeding of Power Grid Tubes" you will note thier emphasis on tube cooling and the effect on tube seals of inadequate cooling. It starts on page 137.

Amateur amp manufacturers had a different perspective. They identified a niche market which was more tolerant of shorter service life and less tolerant of noise associated with the blowers while producing a product that none of the commercial manufacturers could or would try to touch price wise.

Heath comes to mind when I think of the concept of 'Getting the Mostest for the Leastest'.
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WD4HXG
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« Reply #4 on: September 18, 2008, 11:05:02 AM »

Eimac designed their products to be used in commercial service by end users who demanded high reliability.

If you look at the Eimac booklet on "The Care and Feeding of Power Grid Tubes" you will note thier emphasis on tube cooling and the effect on tube seals of inadequate cooling. It starts on page 137.

Amateur amp manufacturers had a different perspective. They identified a niche market which was more tolerant of shorter service life and less tolerant of noise associated with the blowers while producing a product that none of the commercial manufacturers could or would try to touch price wise.

Heath comes to mind when I think of the concept of 'Getting the Mostest for the Leastest'.
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KB9CRY
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« Reply #5 on: September 18, 2008, 11:46:36 AM »

Heath comes to mind when I think of the concept of 'Getting the Mostest for the Leastest'.


Actually that design is superb and it's been measured that there is adequate air flow across the tube pin seals to do the job (but does require the fan to operate properly = properly maintained and lubed).
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WB2WIK
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« Reply #6 on: September 18, 2008, 06:47:50 PM »

Drake, Henry Radio and some others used the blower/chimney approach with 3-500Zs.  Heath, Swan and many others did not.

If the amplifiers were well designed, the tubes can last 20+ years either way.

It is crucial to cool the anode seal (top pin of the tube) and the base pin seals (obviously, at the bottom of the tube) as these are all very hot places.  Heath did it just fine, so does Ameritron and so did Swan: The key is to blow air not only across the glass envelopes, which hardly need any air cooling, but also across those seals, which do.  The good guys did it right.  Chimneys are really not required.

WB2WIK/6
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K0WA
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« Reply #7 on: September 19, 2008, 07:24:57 AM »


I recently purchased a used AL-82 in mint condition. I looked at a lot of amps when I was in the market.  I looked at tube replacement costs and design.  I selected the AL-82 because of tube replacement cost is lower that most (not 811A or 572)...and the fact that the designer did the right thing with the amp by using chimneys.  Although many manufacturers have gotten away without chimneys, I do not think they could run the amp at higher output levels.  My venerable SB220 was good for 500 mills (sometimes higher) but that was what was recommended.  I felt the 220 was always hot and had a muffin fan on the top of unit over the PS.  Now, I understand the PS in the 220 was not the heaviest...but the AL-82 you can run 800 mills on the the unit with ease.  By using the chimneys (and a stiffer HV supply) the 3-500Zs can really sing and last a log time.

I love to read the forums.  Lots of good information.

Lee - K0WA
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K9FON
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Posts: 1012




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« Reply #8 on: September 19, 2008, 09:32:11 AM »

Yes the forums are a wealth of great info IF it doesnt turn into a name calling brawl! Hi.
WB2WIK has some great info to share as well as a few others. My Swan MK II seems to run pretty cool even with no chimneys.  
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VR2AX
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Posts: 1013




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« Reply #9 on: September 19, 2008, 08:08:54 PM »

Chimneys are not a panacea for all cooling issues, even where they are used in designs like the Drake l-4 and L-4B:

http://www.k3hkr.com/KeepKool.html

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