On 6/7/2017 8:31 PM, Josh Gibbs wrote:
Just when you thought this thread was done... some interesting new
information!
It seems that Ten-Tec started adding in additional shielding for the
transformer at some point. Mine does not have the shield!
For reference here is one with the shield:
https://drive.google.com/open?id=0B_pjAwEfeYcdWTNrUUhPQlk4ZlU
And here is mine:
https://drive.google.com/open?id=0B_pjAwEfeYcdOUdHVW5VUlJmcVk
I'm going to make up a shield like this with some aluminium and see if it
helps with the hum.
Aluminum is non-magnetic, so not sure if it will do what you expect. I
thought you had to use iron or mu metal (used to shield scope tubes) for
magnetic shielding. From Wikipedia:
*Mu-metal* is a nickel <https://en.wikipedia.org/wiki/Nickel>–iron
<https://en.wikipedia.org/wiki/Iron> soft magnetic alloy
<https://en.wikipedia.org/wiki/Alloy> with very high permeability
<https://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29>,
which is used for shielding sensitive electronic equipment against
static or low-frequency magnetic fields
<https://en.wikipedia.org/wiki/Magnetic_field>. It has several
compositions. One such composition is approximately 77% nickel, 16%
iron, 5% copper <https://en.wikipedia.org/wiki/Copper> and 2% chromium
<https://en.wikipedia.org/wiki/Chromium> or molybdenum
<https://en.wikipedia.org/wiki/Molybdenum>.
The high permeability of mu-metal provides a low reluctance
<https://en.wikipedia.org/wiki/Reluctance> path for magnetic flux
<https://en.wikipedia.org/wiki/Magnetic_flux>, leading to its use in
magnetic shields <https://en.wikipedia.org/wiki/Magnetic_shielding>
against static or slowly varying magnetic fields. Magnetic shielding
made with high-permeability alloys like mu-metal works not by blocking
magnetic fields but by providing a path for the magnetic field lines
<https://en.wikipedia.org/wiki/Magnetic_field_line> around the shielded
area. Thus, the best shape for shields is a closed container surrounding
the shielded space.
Uses and properties
Mu-metal is used to shield equipment from magnetic fields. For example:
* Electric power <https://en.wikipedia.org/wiki/Electric_power>
transformers <https://en.wikipedia.org/wiki/Transformer>, which are
built with mu-metal shells to prevent them from affecting nearby
circuitry.
* Hard disks <https://en.wikipedia.org/wiki/Hard_disk>, which have
mu-metal backings to the magnets found in the drive to keep the
magnetic field away from the disk.^[/citation needed
<https://en.wikipedia.org/wiki/Wikipedia:Citation_needed>/]
* Cathode-ray tubes <https://en.wikipedia.org/wiki/Cathode-ray_tube>
used in analogue oscilloscopes
<https://en.wikipedia.org/wiki/Oscilloscopes>, which have mu-metal
shields to prevent stray magnetic fields from deflecting the
electron beam.
73,
Carter K8VT
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|