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Bird Termaline load repair

 

GM! After seeing that I am positively certain the reason you don't have a flat match is someone kluged the short resistor in place with a copper pipe to extend it to the feed point. Putting the correct resistor in it should restore the factory performance.? ?Reid? W6MTF?
 

Indeed, I kludged together an interface to a 12" long resistor and now I'm under 2:1 to 2 GHz.? There are a couple of "resonances" but I think that's because of the kludge (I was wanting to see if the short resistor was truly the cause of the problems).? More to be done but I'm on the right path.
Thanks Reid!
 

The End--success!
The fix was a combination of (1) a 12" long resistor that could run the entire length of the tapered outer conductor, and (2) the shortest, neatest transition from the 0.875" id fingerstock cup to the 1.0" od of the resistor at the wide (input) end.? Copper plumbing adapters came in handy.
PS it DOES make a difference to have the assembly in the oil--outside the oil the worst VSWR (up to 2 GHz) was 1.9:1, and once in the oil the worst VSWR dropped to 1.45:1.? Still not "to spec" but certainly usable.
A bit more digging revealed that this load was roughly 1975 vintage.? Back then there must have been some company that made 7/8"x12" non-inductive resistors that would fit into that fingerstock cup...or perhaps Bird had them made custom.? The latter would make sense as you cannot buy only a replacement resistor from Bird--you have to buy the entire drop-it-in-the-oil assembly (for the low, low price of $1700+).
Bird was of absolutely no help, but I suppose I should cut them some slack given that this thing is pushing 50 years old.
?
 

Great work, Scott! Do you have a photo of the finished?product before final assembly to share?


On Sun, Jul 21, 2024, 3:28 PM Scott Townley via <scott=[email protected]> wrote:
The End--success!
The fix was a combination of (1) a 12" long resistor that could run the entire length of the tapered outer conductor, and (2) the shortest, neatest transition from the 0.875" id fingerstock cup to the 1.0" od of the resistor at the wide (input) end.? Copper plumbing adapters came in handy.
PS it DOES make a difference to have the assembly in the oil--outside the oil the worst VSWR (up to 2 GHz) was 1.9:1, and once in the oil the worst VSWR dropped to 1.45:1.? Still not "to spec" but certainly usable.
A bit more digging revealed that this load was roughly 1975 vintage.? Back then there must have been some company that made 7/8"x12" non-inductive resistors that would fit into that fingerstock cup...or perhaps Bird had them made custom.? The latter would make sense as you cannot buy only a replacement resistor from Bird--you have to buy the entire drop-it-in-the-oil assembly (for the low, low price of $1700+).
Bird was of absolutely no help, but I suppose I should cut them some slack given that this thing is pushing 50 years old.
?

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