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 Post subject: Shielded cables
PostPosted: Tue Oct 12, 2021 8:18 am 
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Joined: Tue Sep 28, 2021 5:23 pm
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As this is my first build any pictures or video of correct way to use shielded cables and where they are most beneficial. Thanks Frank


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 Post subject: Re: Shielded cables
PostPosted: Tue Oct 12, 2021 3:04 pm 
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Most kits come with RG174 cable, which is very flexible but can be prone to shorting if you are not careful with the soldering iron, as too much heat on the braided shield can melt the insulation on the conductor wire.

Here's a link to a discussion on prepping shielded wire, with a great image on the steps you need to take:
https://el34world.com/Forum/index.php?topic=27186.msg298702#msg298702

Here is another page on general amp building....the section on how to prepare RG174 shielded wire is about 3/4 of the way down. Has good pictures. https://el34world.com/Hoffman/instructions.htm

Another option to the RG174 is RG316, which is also shielded coaxial cable but it has PTFE as the insulator on the conductor. This is nearly impossible to melt. The main drawback is that it isn't as flexible. I bought mine on Amazon. Its a little pricier than RG174.
Here's a good site which shows pictures of how the RG316 is prepped, and the input wires are connected. Scroll down about 3/4 of the way:
https://sluckeyamps.com/VAC15/ac15.htm

When using shielded wire, the key is to ground only one end of the shield. This prevents ground loops. For input wires, I ground the shield at the jack. This is how most layouts do it. The shield should be grounded at the same location the other grounds occur for that particular stage.

I always use shielded wire from the input jacks straight to grid stopper resistors located at the tube socket. If your layout has the input grid stopper resistors mounted on the board, you may want to consider relocating them to a terminal strip adjacent to the input tubes and run your input wires to that.

I also sometimes use shielded wire for the negative-feedback wire if I am getting noise. Similarly, if I have a post-phase inverter MV, I use shielded wire since those runs are usually over the board and prone to getting noisy.


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