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New home-brew 40 meter RF deck

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December 09, 2018, 10:07:41 PM *
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Author Topic: New home-brew 40 meter RF deck  (Read 8721 times)
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« Reply #75 on: February 27, 2018, 06:14:08 PM »

BTW, a dummy something I learned the hard way:  Never suck air from the top down thru the tube bottom and out. I once had a blower on the outside of the house that pulled air out. It was a big (and expensive) external anus 3CX tube. It was quiet and efficient. But the tube failed quickly because the hot air thru the plate pushed hot air onto the filament seals and the fil seals failed. Always push air in from the bottom thru the top as most smart people do.. :-)


Expensive lesson indeed! I have an 833A that shows open filament and it was a NOS from the signal corps. There are no solder connections in these tubes. Everything is spot welded. The filaments in an 833 are in parallel and it is possible to have a tube that only lights up on one side. You can usually tell if one side is open as the filament tension springs will be fully extended. In fact that's a test or sign to look for if your window shopping online. Well anyway, this 833 has perfect spring tension and I figure iI hook a model A buzzer ignition coil to the filaments and the other side to the plate, I may be able to see where it is arcing? Now how to fix it? I thought about trying to discharge a high voltage capacitor across the filament contacts to see if that would spot weld it together?  Sorry Ron, not trying to steal your show Grin Grin

The secrecy of my job prevents me from knowing what I am doing.
Patrick J. / KD5OEI
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« Reply #76 on: February 27, 2018, 11:16:49 PM »

I hope you can fix those tubes Ron. Rare types!

Radio Candelstein - Flagship Station of the NRK Radio Network.
Two shots of Whisky

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« Reply #77 on: March 24, 2018, 11:06:15 AM »

Hi Ron,

Really like your thread here. Very helpful, especially the frequent pics!

Can you describe more fully how you built the plate choke? What form did you use, and is it filled with anything? I read KK5DR's article on building them with an iron ferrite core. Did you go that way?

John - W9JSW
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Penta 254W

« Reply #78 on: March 25, 2018, 12:30:43 AM »

Hi John,
The plate choke is just a standard ceramic standoff insulator with #24 enameled copper wire close wound as long as I could make it. I think this one ended up being about 450 uH which is enough for 40 meters. The most plate current I will use is about 250 mA, so I probably could have used #26 or even #28, but I like a margin of safety. There is no ferrite core. The similar plate choke I wound to use on my 160 meter transmitter is about 8 inches tall and about 1.5 inches in diameter and measures almost 1000uH. I usually put 2or3 strips of epoxy over the coil once it is done.

Thanks for your interest. Ron w8acr

The AM voice of Knox, North Dakota
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