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Bird Termaline Resistors




 
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Author Topic: Bird Termaline Resistors  (Read 614 times)
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AB3L
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« on: July 20, 2017, 01:54:59 PM »

Hello, I have an 8135 load rated for 150w. The resistor is now reading over 80 ohms instead of 50. Has anyone found a way around buying one from Bird for $230. ?
Thanks,

Bob
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Pete, WA2CWA
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« Reply #1 on: July 20, 2017, 03:05:17 PM »

You can buy a 100 watt non-inductive 50 ohm resistor from Mouser for $560 so Bird's price doesn't sound that bad. Maybe they have cheaper ones in China.
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« Reply #2 on: July 20, 2017, 03:06:21 PM »

Bob,

   Big dummy loads sometimes generate a small voltage at the terminals, especially when hot. I'm not sure of the mechanism, but with your DVM on ohms, try swapping the leads. Does it still read 80 ohms?

    If the change is real, 80 ohms resistive should indicate as a 1.6:1 SWR when driving it with RF..

   I got a 3KW big Bird 30 db attenuater here at work. It will only read 50 ohms when cold. A wattmeter downstream of it reads up to a 1/2 watt after soaking the attenuator at 3KW for several hours.

Jim
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Jim, W5JO
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« Reply #3 on: July 20, 2017, 05:02:45 PM »

MFJ sells non-inductive resistors in several sizes, much cheaper than that.  Check to see if they have the size you want.  The MJF cantenna is modeled after the Heath and they sell a 100 watt resistor for it.  It is the same size as the old Heath version.  You will have to search for their parts section of the website, it is a bit difficult to locate, you may have to call them.
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AB3L
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« Reply #4 on: July 21, 2017, 10:30:16 AM »

I checked the resistance and it is the same either way the leads are switched. I took the resistor out to clean the contact ends but still no difference. Looks to be a glass rod with film on it.
I guess I'll look around for a substitute.

Bird sells a brand new 8135 for about $560. or so. They have had a long run on that model.

Thanks,

Bob
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K6IC
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« Reply #5 on: July 22, 2017, 02:45:39 PM »

Bob,

Have seen several generic Dummy Loads which read 70 - 80 Ohms.

Generally,   this means that they have seen more input power than they can dissipate,   and permanently damages the resistor.

The resistor in the MFJ version of the Cantenna has a smaller sized resistor than did the real Cantenna,   something like 50 W verses 100 W,  IIRC  --  used to have an MFJ.

Here is a Bird load in occasional use here (wish that it was an Attenuator).

FWIW,   Vic


* Dups 2011 plus Bird 005.JPG (1212.98 KB, 2304x3072 - viewed 44 times.)
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Jim, W5JO
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« Reply #6 on: July 22, 2017, 03:56:56 PM »

The resistor in the MFJ version of the Cantenna has a smaller sized resistor than did the real Cantenna,   something like 50 W verses 100 W,  IIRC  --  used to have an MFJ.

Check the MFJ site for part number 119-1500.  It is a 50 ohm, 200 watt non-inductive resistor 1" diameter for ~$32

PN 115-1500 is 3/4 inch diameter, 50 ohms, 90 watt resistor for ~$20
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« Reply #7 on: July 22, 2017, 06:22:01 PM »

Check this out:

http://www.martinrfsupply.com/Bird-RF-Wattmeters_c_1.html

The proprietor (I think his name is Chuck) is very helpful.  He might be able to help you find an exact replacement part.  I have a good buyer/seller experience with these folks

GL es 73, Al
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K6IC
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« Reply #8 on: July 22, 2017, 07:48:41 PM »

And,   there is Tim Brown,  MN3E,  if one was looking for a replacement Load,   doubt that he has the Bird resistor:
http://www.nm3e.com/loadSampler.htm#LoadSampler

Have dealt with him in the past  --  very helpful,   and is honest in my experience.

GL,   Vic
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