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Ohmite 1,000 Watt dummy load




 
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Author Topic: Ohmite 1,000 Watt dummy load  (Read 476 times)
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N0WEK
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« on: November 19, 2017, 05:15:25 PM »

I just got this locally off Craig's list for $40.

It has 10 of the 100 watt, 500 ohm Ohmite dummy load resistors in it, which gives me 50 ohms @ 1,000 watts. It's got no manufacturers tag or anything else to identify it.

I'll clean it up after my hand recovers from thumb surgery.

Anybody have any info?

Greg



* Dummy load.jpg (169.43 KB, 1200x900 - viewed 111 times.)

* Dummy load 2.jpg (146.66 KB, 1200x900 - viewed 93 times.)

* Dummy load 3.jpg (123.53 KB, 675x900 - viewed 97 times.)
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WO4K
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« Reply #1 on: November 20, 2017, 09:29:56 AM »

Here's the 100 watt version....


* Dummy Load.jpg (97.85 KB, 810x1080 - viewed 78 times.)
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WA2SQQ
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« Reply #2 on: November 20, 2017, 11:37:40 AM »

Moint a fan behind it and you've got a great space heater!
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N0WEK
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« Reply #3 on: November 20, 2017, 02:33:10 PM »

Moint a fan behind it and you've got a great space heater!

Considering that the Gates eats 4,800 Watts at full scrote I may as well keep it all in the shack on cold days instead of wasting it in the aether. Smiley
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N0WEK
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« Reply #4 on: November 23, 2017, 01:22:01 PM »

I did manage to find a spare resistor at the local museum. It was the only one they had and of the 13 values that Ohmite made it happened to be the one my unit uses.

I'll have to get the unit cleaned up and hopefully all the resistors in it are good.


* DSCN6966.JPG (2558.27 KB, 4000x3000 - viewed 68 times.)
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Opcom
Patrick J. / KD5OEI
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« Reply #5 on: November 25, 2017, 11:50:58 AM »

That's a real classic!
Do they glow?
Is the inductance of the resistors an issue on HF?
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W1ITT
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« Reply #6 on: November 25, 2017, 12:18:07 PM »

To answer Opcom's question about inductance of the resistors...   The resistors are all in parallel, which tends to reduce the problem.  And spacing from the center post is set to maintain 50 ohm impedance as well.   Bird and others made similar air blast dummy loads for high power broadcast use, but the modern ones are made with Carborundum resistors.  With proper layout, and occasionally some compensating elements, these can be made to be 1.1:1 or less up through the 108 mhz broadcast allocation.  You'd probably be surprised at how good the Ohmite model is up through the bands.  With some air cooling to augment radiation cooling, it's a worthy piece for the ham shack.
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N0WEK
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« Reply #7 on: November 26, 2017, 04:18:51 PM »

That's a real classic!
Do they glow?
Is the inductance of the resistors an issue on HF?
http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/tubes/records/D100600.pdf

The specs I found somewhere else said that at full power they should just glow dull red in a dimly lit room.


* Ohmite dummy load.JPG (96.2 KB, 784x874 - viewed 36 times.)
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