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   Home   Help Search  
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Author Topic: Cantenna dummy load resistor  (Read 6929 times)
N0YXB
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Posts: 1122




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« Reply #30 on: September 19, 2017, 07:49:04 AM »

Why the debate. Just get a gallon on mineral oil and your set for life.

Indeed!
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W8JX
Member

Posts: 12080




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« Reply #31 on: September 19, 2017, 09:53:33 AM »

Why the debate. Just get a gallon on mineral oil and your set for life.

Indeed!

No less with non detergent oil and likely more set because motor oil can withstand higher temperatures on resistor surface than mineral oil. But, some simply cannot think outside the box here.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
ND6M
Member

Posts: 556




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« Reply #32 on: September 19, 2017, 12:44:02 PM »

sigh Sad Sad
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K8AXW
Member

Posts: 6313




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« Reply #33 on: September 20, 2017, 09:55:05 AM »

Sometimes there's no need to think outside the box is others have shown that staying within the box works fine.
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K0OEH
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Posts: 5




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« Reply #34 on: September 23, 2017, 09:49:49 AM »

Use mineral oil. It was recommended by Heathkit for their original Cantenna dummy load. Mineral oil is available on line and at most drug stores.
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AF6LJ
Member

Posts: 366




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« Reply #35 on: September 23, 2017, 10:27:57 AM »

Why the debate. Just get a gallon on mineral oil and your set for life.

Indeed!

No less with non detergent oil and likely more set because motor oil can withstand higher temperatures on resistor surface than mineral oil. But, some simply cannot think outside the box here.
That's what is in my home built dummy load..
When it gets hot it reminds me of my dad's garage. Smiley
Besides it is cheaper tham mineral oil.
Logged

Take Care
Sue,
AF6LJ
K2DFC
Member

Posts: 97




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« Reply #36 on: September 23, 2017, 10:55:28 AM »

Why the debate. Just get a gallon on mineral oil and your set for life.

Indeed!

No less with non detergent oil and likely more set because motor oil can withstand higher temperatures on resistor surface than mineral oil. But, some simply cannot think outside the box here.
That's what is in my home built dummy load..
When it gets hot it reminds me of my dad's garage. Smiley
Besides it is cheaper tham mineral oil.

Hi Sue, glad to see your OK. You dropped off the face of the earth on the QRZ forums.
Fred
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AF6LJ
Member

Posts: 366




Ignore
« Reply #37 on: September 23, 2017, 11:09:09 AM »

Why the debate. Just get a gallon on mineral oil and your set for life.

Indeed!

No less with non detergent oil and likely more set because motor oil can withstand higher temperatures on resistor surface than mineral oil. But, some simply cannot think outside the box here.
That's what is in my home built dummy load..
When it gets hot it reminds me of my dad's garage. Smiley
Besides it is cheaper tham mineral oil.

Hi Sue, glad to see your OK. You dropped off the face of the earth on the QRZ forums.
Fred
I didn't drop off...
Smiley
You know they have a different set of standards for some individuals.
I'll leave it at that.
Logged

Take Care
Sue,
AF6LJ
N2EY
Member

Posts: 4442




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« Reply #38 on: September 23, 2017, 12:08:30 PM »

Use mineral oil. It was recommended by Heathkit for their original Cantenna dummy load. Mineral oil is available on line and at most drug stores.

Yes, if you can't get transformer oil, use mineral oil. The Heathkit manual makes it very clear that motor oil is not to be used.

From Page 9 of the manual:

"If transformer oil is not available, mineral oil may be used, but do not use any type of motor oil. The vaporizing temperature of motor oil is too low and would cause excess vapor."

The underlining of "do not" is from the manual. Heath was pretty specific - they knew what they were talking about.

Besides.....think about the reaction at the drug store checkout when you show up with a whole gallon of mineral oil.....and tell them you need it for "a special project".

---

btw - you can't use just any Carborundum-type resistor in an oil-cooled dummy load. The resistor used by Heathkit is a special coated type . Without the coating, the oil eventually seeps into the resistor and changes the resistance value. Not good.


The modern part number (made by Kanthal Globar) is 886-SP-500-K. The SP denotes the special coating, which is important.

MFJ also sells the resistor, as their p/n 115-1500A. The A denotes the special coating.

http://www.orcadxcc.org/content/cantenna_va7jw.pdf

has lots more info.

73 de Jim, N2EY
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K4TLJ
Member

Posts: 94


WWW

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« Reply #39 on: September 23, 2017, 07:59:20 PM »

Anyone ever try distilled water in a cantenna? It is nonconducting. Just curious.
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W9IQ
Member

Posts: 1706




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« Reply #40 on: September 23, 2017, 08:18:28 PM »

Deionized water has a relatively low thermal capacity that would reduce maximim power / maximum time curves. It will also cause the can to rust, gradually turning the water into a partial conductor.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K6BRN
Member

Posts: 461




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« Reply #41 on: September 23, 2017, 11:37:41 PM »

Mineral oil - even the stuff available from drugstores, works fine in the "Cantenna" from Heathkit or MFJ.  Its pretty much what MFJ packs with the Cantenna anyway.  Heath used to recommend mineral oil if transformer oil was not available.

A problem with the Cantenna is that the oil will vaporize from the inside, out the vent and re-condense on the top lid, even if the Cantenna is not in use.  If the pressure vent is blocked, the oil will be forced up the connector - not good.  For that reason, I used to keep it in a metal bucket to keep the oil off of the floor.  A plastic bucket is attacked by the oil and is not a good choice.

Water would become a conductor at light-speed in the Cantenna - plenty of metal ions to break loose from the can and resistor brackets - likely already dissimilar metals.  And motor oil vapors are mildly toxic - best to avoid.

Brian - K6BRN
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K8AXW
Member

Posts: 6313




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« Reply #42 on: September 24, 2017, 11:43:42 AM »

EY:  It would be better if you didn't tell the druggist anything!  Just have a very distressed look on your face!   Grin
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N2EY
Member

Posts: 4442




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« Reply #43 on: September 24, 2017, 12:19:57 PM »

N2EY:  It would be better if you didn't tell the druggist anything!  Just have a very distressed look on your face!   Grin

I like that! Subtle, but effective!

73 de Jim, N2EY
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