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Author Topic: Globe King 500(C) mod for 160M  (Read 363 times)
KZ6AM
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Posts: 3




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« on: December 15, 2009, 12:28:36 AM »

I'm soliciting what other GK500 'x' owners may have done to enable their GK to drive a 50 ohm resistive 160M antenna load without using the 'external antenna tuning device' advised by WRL for this rig.

I know more C is required across the present antenna loading variable cap. The rig does not have enough C even with the aid of the ant coupling switch (introduces mica caps, in steps, as required for 80-10M).

Merely bridging presently installed micas in the rig's 'fixed C' antenna coupling circuit destroys the original 'steps' for such a circuit (..big deal). And if one ties a C (eg: 300ufd mica) at the output of the 160M inductor, the minimum loading C is raised by the amount of that C (since present switches don't allow for switching in this added C w/o changing the original intent of the rotary switch). Realize my tests show both of these approaches enables full loading on 160M (w/o a tuner). Its just that the rig design is, I believe, degenerated. One does wonder why WRL didn't use the 160M tab available on the bandswitch to control the L6 (160M inductor) and use the tab on the ant coupler switch, availed by this bandswitch control of L6, to then switch in yet another fixed mica for 160M antenna loading. Maybe I am still 'kunfoo'ed'.  

I'd surely appreciate what you did, even if it iterates what I've cited above.

Thanks all!!
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N7IOH
Member

Posts: 116




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« Reply #1 on: December 15, 2009, 06:32:39 AM »

You may want to join AMPhone.  These guys have been a lot of help to me and I think they have seen and done just about everything when it comes to these old radios.

http://amfone.net/Amforum/index.php

Al, n7ioh
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WB8UHZ
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Posts: 125




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« Reply #2 on: December 15, 2009, 10:13:49 AM »

There was a real good article on this in Electric Radio Magazine recently. I don't get  ER so I'm not pushing it here. I had a QSO with W4FMS Frank in Grand Rapids, Michigan. He completed the mod and it works great. I think he is good in QRZ.

73 Tim
WB8UHZ
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KZ6AM
Member

Posts: 3




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« Reply #3 on: December 15, 2009, 02:17:38 PM »

Thanks for the leads guys!

Today I even loaded the rig with 300 ohm resistive (rig cites need to see this load on 160M). Laoding is still too lite (realize about 200ma, rather than 300ma, at the dip). I couldn't get 300ma max tube load even by adding a large air variable to a few places in the tank (including across the antenna loading variable on the tank output).

The way I DO get full load: I used a parallel L C across the output of the rig and tap the antenna at the coil (about 20% total coil length). I believe this transformer (like a balun) is transforming the Z (like about 5:1 based on the turns ratio). Anyway: The rig provides maximum forward power at the dip now. And the external tuning assembly does not get hot at all. The cable between the rig and the tuner is 6'...and it does not get hot (6' amounts to less than .0002 wavelengths on 160M). BTW: For what it is worth, my SWR bridge happens to in the line between the rig and this tuner....SWR at 300ma plate tank dip is less than 2:1.
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WB8UHZ
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Posts: 125




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« Reply #4 on: December 15, 2009, 02:47:14 PM »

Just a long shot idea and maybe not the right thing to do but what if you put a 4to1 balun at the antenna connection on the GK ? I often wondered about this as the Globe Champion I have works the same on 160 meters. It want to "see" a 450 ohm load.

Tim
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KZ6AM
Member

Posts: 3




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« Reply #5 on: December 19, 2009, 02:31:14 PM »

Hi Tim

Yes. For 160M I've used a 4:1 balun with success. Subsequently I used it on another project so it has been removed from service. But the problem is the balun messes up the match of my 50 ohm antennas on other than 160M because the rig on 160M is 300 ohms out. On the other bands it is 50 ohms. See how the balun now messes up the loading.
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W8JI
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« Reply #6 on: December 19, 2009, 06:13:15 PM »

Globe equipment was notoriously poor on 160 and 80.

Look at what I do with my Globe Scout.....

http://www.w8ji.com/globe_scout_modifications.htm

I'm not sure it is applicable to the Globe King, but as I recall the King and everything else really didn't work well on 160 without adding significant loading capacitance.
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