[Test-Equipment] Bird Termaline Question - Update (long)

[Richard Knoppow]

    Since you got into the thing is is possible to measure the 
resistance of the resistor directly?
    What I suspect is that the resistor is not really a single resistor 
but effectively several resistors on parallel. This is done by taking a 
coated blank resistor and slitting the coating lengthwise into several 
sections. If one burns out the value goes up by an amount which depends 
on the value of each section. I think they may open at one end rather 
than actually opening along the length somewhere. The cartridge 
resistors used in the Cantenna and in the MFJ look identical. Both have 
a coating over the resistor coating and silvered end sections for 
connecting.  It is not possible to see the internal connections.
     I don't know who actually makes the resistors but have found 
similar ones on the web. Bird may make their own and advertise that they 
are film deposited on glass. Its possible they are of a different 
construction than I imagine but the failure seems to indicate a multi 
section resistor.
     That was indeed a pretty amazing game.
On 2/7/2017 10:35 AM, Doug Hensley wrote:
> I want to thank everyone for the many helpful replies as well as information about this unit.  I have taken my time with it and did not want to respond until I had something to add to the topic.
>
>
> I listened to all suggestions and followed up performing them where I could. I cleaned the N connector thoroughly, first with acetone and then with DeOxit 5, but that made no change to the measure.  I compared what my Fluke meter was getting with a new Chinese DVOM that I think is quite accurate and the result was the measures agreed.  I then checked the oil and the level was fine.  The smell was strong and I expected more of a bland smell and what I got was a strong smell which
>
> may be a result of the over-heating.  The construction is a single cartridge resistor being held in the center of a cone shaped perforated metal shield.  It looks relatively easy to service given you have the parts.
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> I then took my antenna analyzer, a Rig Expert 220 Zoom and it, more or less, agreed with my two DVOM's.  At 100 kHZ, Z & R were both 72.6 ohms.  X was -2.41 ohms.  At 21 mHZ, Z was 68.3 ohms, R was 67.7 ohms, X was -9.4 ohms.   So my DVOM's were absolved of any suspicion.  The analyzer was connected through direct coupling of N female sockets via a two-way male N Gender changer.
>
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> Both Martin & Bird responded.  Martin said get the oil off ebay ($13 + 35 shipping); get the resistor from Bird.  Bird said the oil was $55 and the resistor was $150.  Wow, that's a lot for a 150W load repair.
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> I asked both companies why the bad Bird units were all being advertised as 75 ohm units and both responded, simply "Well, they are bad".  The deeper meaning to my question is how are so many units coming from so many different environments & users measuring the 70-73 ohm measure ? That must be the resistance across the cone, isn't it?  Otherwise, when the resistor pops, where does the measure come from?  The units could not all have been abused in the same way or for the same application.  I can understand the cartridge blowing like a fuse but I would like to know (for curiosity sake) where the 70-72 ohm measure is coming from.  Bird declined to comment, perhaps because it does not matter.  To put the unit back in service you have to change the oil, change the resistor, change the seal and hope you did it right.  At $205 plus shipping, I sure like the idea of just using my old Heath Cantenna !!
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> My investment is a total loss but if anyone can offer me something for it, it is available.
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> Thanks to all for the great responses.
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> At least my Patriots came through in the clutches.  That made my weekend !!
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> 73, Doug W5JV
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL