Conductive Paint for Inside of Head Cabinet?

[rp]

That paint is pretty expensive isn't it?

exactly. though it sure looks spiffy in guitar cavities.

I usually just buy a sheet of aluminum flashing from the Depot.

exactly

Then either glue it down or staple it down.

no glue, if you have to modify/re-tolex /re-purpose the cab that glue will be an annoyance.

Aluminum foil will work but is less durable.

especially for tweakers that pull the head in and out all day.

[The New Steve H]

Aluminum foil will work but is less durable.

especially for tweakers that pull the head in and out all day.

The exact thing that occurred to me. I know I'll be dragging the chassis over it.

[Gaz]

That paint is pretty expensive isn't it?

I usually just buy a sheet of aluminum flashing from the Depot.

Then either glue it down or staple it down.

Aluminum foil will work but is less durable.

Ever try to test flashing with your meter set to Ohms/continuity? If it's the nice thin work-able stuff, it's got a coating on it that is not conductive. You have to sand it off or it does nothing. Well, works to prevent the cab catching on fire as easily

[pdf64]

The Nashua 324A tape previously mentioned doesn't seem to have that issue.

[The New Steve H]

The whole thing was actually going to hinge on whether I had a big enough piece of aluminum sitting in my garage, and lo and behold, it turns out I do, so that technical issue is settled.

[Littlewyan]

I buy my aluminum sheets off ebay. They cut it to a size I specify and its only roughly £10. I then glue that to the bottom of the cab. Works great. I did use sticky back aluminum foil originally but it eventually came off after 6 months of service.

I think Marshall just use a sheet of aluminum that stops short of the holes for the chassis screws. My sheet goes over those holes and I just drill holes into the sheet for the screws.

[Garthhog]

In my day job I am an EMI test engineer for a large defense contractor. We have 3 large screen rooms (Faraday cages) in the lab. They are constructed of WOOD painted with conductive paint, and assembled with an iron frame, bolted every few inches. These cages are rated for up to 40 GHZ operation. The keys to them working wrll is minimizing the gaps where the conductive plywood is bolted to the iron frame. The wavelength of an electromagnetic wave at 40 GHZ is 7.5mm, and a quarter wavelength (ideal for propagation ) is about 1.9mm. To ensure the wave goes evanescence (no longer capable of propagating energy), the gas must be MUCH LESS than 1.9mm. This is a difficult problem, yet is accomplished using painted plywood bolted to a metal frame.

Now, a guitar amplifier cares nothing for 40 GHz. At 300 MHz, the quarter wavelength is 750mm, and 300 MHZ is inconsequential to a tube amp in terms of interference. Someone mentioned 10 kHz earlier but got the wavelength very wrong (for an ELECTROMAGNETIC wave, which is what we are addressing by shielding the amp cavity). 1/4 wave length at 10kHz is about 30 km (I did the calculation a few times because this is REALLY long). Now the wavelength of a SOUND wave in air is much shorter, about 3.4 cm, which is what I think the previous poster was citing... but we don't use Faraday cages to shield against sound waves.

So, to answer your question about using conductive paint, yes it will work as long as the electrical conductivity between the chassis and the painter surface is good. Ideally, the resistance should be less than 2.5 miliOhms. Minimizing the gaps is good practice, but more to prevent surface oxidation, which will reduce conductivity.

Ryan

Edit: sorry for the typos. I can't get to ampgarage.com during the day unless I am unlink my phone, and editing typos on my phone is a PITA.

[The New Steve H]

Always nice to hear from someone who knows. Thanks.

It looks like you're right about the ridiculous wavelength figure I came up with at first. I was not paying attention, and I used the wrong online calculator.

When I repeated the calculation for EM waves instead of sound, the discrepancy between the new result and the old one was a bit startling.