Building a Faraday Tube Cage - Input needed

Talk about tubes and their effect on your tone

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Addictedtokaos
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Building a Faraday Tube Cage - Input needed

Post by Addictedtokaos » Thu Apr 05, 2012 9:49 am

The other day I noticed that my amp was picking up interference from my Wifi. When I put a NOS tube in V1 it was especially bad.

I came across this.
http://thetubestore.com/tubecage.html

To me it just looks like some copper mesh fixed to the outside of the tube shield with some shrink tube. And possibly a small copper mesh disc in the top under the spring.

Question: My only concern at this point is the copper mesh covering the top of the tube shield. Will this cause venting issues with the tube? I know preamp tubes get warm, but are they sensitive to to much heat that blocking this hole may cause???

I order some material on the cheap: 1 6"x6" sheet of 100x100 grid size copper mesh, and 1 meter of 35mm shrink tubing.

I personally want to test to see if the will reduce or completely eliminate RF interference, so I will make sure to post my findings.
Last edited by Addictedtokaos on Thu Apr 05, 2012 3:30 pm, edited 1 time in total.
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Re: Building a Faraway Tube Cage - Input needed

Post by bcdon » Thu Apr 05, 2012 3:11 pm

What sort of interference are you getting from your WiFi access point? These devices operate in the 2.4/5Ghz range and it's strange that you pick up any RF interference. Then again, RF is a black art so I'm curious as to what you are observing.

Cheers,

don


* Faraday. http://en.wikipedia.org/wiki/Faraday_cage :)

Addictedtokaos
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Re: Building a Faraway Tube Cage - Input needed

Post by Addictedtokaos » Thu Apr 05, 2012 3:22 pm

lol. thank
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Re: Building a Faraday Tube Cage - Input needed

Post by r_cod_81 » Tue Apr 10, 2012 5:09 am

Addictedtokaos wrote:I came across this. http://thetubestore.com/tubecage.html
They seem awfully pricy - I got some of these and they work perfectly:
http://www.ampmaker.com/store/9-pin-valve-shield.html
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94Tremoverb
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Re: Building a Faraday Tube Cage - Input needed

Post by 94Tremoverb » Thu Apr 12, 2012 6:24 pm

Considering that the standard preamp tube shield is a solid metal can, and even the top is well shielded by the spring when it's compressed onto the top of the tube, and thus the tube already has an excellent Faraday cage, these expensive copper mesh things can be certified as pure 100% Extra Virgin Snake Oil.

Break-through from phones etc is still an issue, but it's the other parts of the amp, and especially the guitar wiring and cable, that are the worst culprits for picking it up.

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SonicProvocateur
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Re: Building a Faraday Tube Cage - Input needed

Post by SonicProvocateur » Sat Apr 14, 2012 8:30 pm

94Tremoverb wrote: Break-through from phones etc is still an issue, but it's the other parts of the amp, and especially the guitar wiring and cable, that are the worst culprits for picking it up.
Old Nextel data streams are the worst offender. But yeah, most towers have been moved out of that 900mhz range because of FCC regulations. From a physicists perspective: adding copper to an already grounded, non-magnetic shield would likely change how many electrons the 12ax7 (or whichever tube) is going to have available at the plates. While it's effect on grounding may be slight, and it's effect of RF even possibly measurable (though also negligible) it's effect on the pull of electrons actually -would- affect the tone I believe. Good to bad? I dunno. Since the tube is going to have a set bias, right?, it shouldn't draw more than available, but I suppose it certainly could sound different...
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Re: Building a Faraday Tube Cage - Input needed

Post by 212Mavguy » Sat May 12, 2012 9:04 am

...I don't think that putting copper around the outside of the tube envelope will alter the sound. The fact that the plate(s) are inside of that copper and with the cathode inside of the grid(s) and plate, mainly the fact of the huge difference the strongly positive plate voltage compared to the cathode and grid(s) causes overwhelming attraction of electrons to the plate... And that voltage difference is even higher between the plate and your copper shielding. If electrons flow like you suggest, they will go to the plate(s.)

I stick on the black aluminum finned Tube Coolers or IERC tube shields, they shield RF and cool the sides of the tube dramatically. Even preamp tubes get hot under their shields, and those shields are what contribute to earlier death because hot glass gets a bit porous and air gets into the vacuum over time at a much faster rate than a cool bottle will do. Proven with plenty of military documentation. Particularly helpful for el84's in hot biased amps like the Maverick, speaking from experience there.

However, with that said, I have out of several hundred collected, two incredibly microphonic preamp tubes that had a habit of going into a resonant runaway situation at anything over slight gain and volumes whether in a combo or not, would change their sound if I surrounded the naked bottle with my hand, acted like a theremin! As I opened and closed my hand around the bottle the sound changed. I think that the situation there was fom excitation of grids via vibration inputs coming from the speaker.
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Re: Building a Faraday Tube Cage - Input needed

Post by domct203 » Tue May 22, 2012 9:19 am

94Tremoverb wrote:these expensive copper mesh things can be certified as pure 100% Extra Virgin Snake Oil
+1

Also, they look like they wouldn't fit in the amp anyway.

I would love to see their data to back their claims, otherwise this looks like false advertising.

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