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Author Topic: Hardrock 50 Amp Build - "dead short to DC"  (Read 293 times)

N4SRN

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Hardrock 50 Amp Build - "dead short to DC"
« on: January 26, 2023, 05:21:22 AM »

I’m building a Hardrock 50 Amp and got to the finals assembly steps and decided to check continuity at a few points before applying power - glad I did!

https://sites.google.com/site/hardrock50beta/hardrock-50-builders-information-site/hardrock-50-builders-portals/sn1200-1399-builders-portal

The build uses RG316 coax segments between the SO239 connectors on the back to a QSK pin diode switching board for CW use and another segment from that QSK board to an AMP-IN power terminal. I was worried I was shorting shield to center conductor but checked continuity to find them isolated from the SO239 to the cable feeding the AMP-IN terminal block. But when I attach the coax shield & ground to that AMP-IN block, I find continuity between the block screws and coax shield & ground. On the HR50 forum, the vendor said it was a “dead short to DC” but I’m a biologist and don’t know what that means or how to fix it. But I’m willing to learn!

How would I go about troubleshooting? I looked for obvious solder bridges and stray lead bits but saw none.

Can solder flux cause a short?

Any help and advice appreciated!

BRET/N4SRN
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Bret/N4SRN
Bedford, NH  USA

W1VT

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Re: Hardrock 50 Amp Build - "dead short to DC"
« Reply #1 on: January 26, 2023, 07:27:41 AM »

He may be trying to say that T2 creates a short to ground.  In other words, what you are measuring is what you should expect with a properly assembled amplifier.  RG316 is Teflon coax that normally doesn't short out.   
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W1RKW

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Re: Hardrock 50 Amp Build - "dead short to DC"
« Reply #2 on: January 26, 2023, 09:30:29 AM »

At the Amp-in Block you should expect to see continuity there.  Pins 1 and 2 form the primary of transformer T1 which will have an extremely low resistance and appear as a short to DC but not at RF.
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N4SRN

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Re: Hardrock 50 Amp Build - "dead short to DC"
« Reply #3 on: January 26, 2023, 10:16:16 AM »

Thanks, y’all - you’re right! Thanks for the explanation - I can see that in the schematic now. The vendor mentioned the “dead short to DC” but didn’t say it was expected. It sounded bad so I halted completion.

All appears well so far!

BRET/N4SRN
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Bret/N4SRN
Bedford, NH  USA

W1RKW

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Re: Hardrock 50 Amp Build - "dead short to DC"
« Reply #4 on: January 26, 2023, 01:06:50 PM »

Put the fire to the wire, Bret!  Keep us posted on the progress.
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AA7IS

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Re: Hardrock 50 Amp Build - "dead short to DC"
« Reply #5 on: January 27, 2023, 06:42:51 AM »

Thanks, y’all - you’re right! Thanks for the explanation - I can see that in the schematic now. The vendor mentioned the “dead short to DC” but didn’t say it was expected. It sounded bad so I halted completion.

All appears well so far!

BRET/N4SRN
You're learning while building, sometimes that's the idea of building anyway.
Now you know a "DEAD" short to DC is not a problem necessarily for RF energy, as a matter of fact you will find many RF connections will measure a dead short to DC and have no issues, depending on the design.
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