Klaas Robers wrote:Steve, I don't know how "open" your mains transformer is. It helps if you construct a winding around the whole transformer, including the iron yoke. I did this in my pseudo Heathkit SSTV monitor and the hum is not completely gone, but it became much less. I have no mu metal shield for the picture tube.
Look to the photo's in the thread "Off Topic", "Retro SSTV anyone?" and then page 14.
The winding is of a single thicker copper wire and it is shorted (visible) from the end to the beginning. I have also seen somewhere a single shorted winding made of copper foil, not too thin and soldered end to beginning. Electricity wire is easier. Eddy current will compensate for the the stray field of the transformer.
Hi Klaas,
Thanks for this idea. It is most interesting and yes - I will now give it a try on my transformer, though it won't look as neat as on yours! Presumably this winding must run perpendicular to the active transformer windings (as indeed it appears to in your case) or it would act like loosely coupled shorted turns and increase the loading..?
Harry Dalek wrote:Great monitor there Steve !
On the mu metal Klaas was mentioning i came across this on another forum .
You have probably heard about something called mu-metal that does provide magnetic shielding. It does exist, but it is fantastically expensive; it's only really practical around things like CRTs in many-thousand dollar oscilloscopes.
Cold-rolled steel is an inexpensive substitute for mu metal. I learned about from a consultant, an engineer familiar with physics, who was helping us shield a monitor lab from the main electrical boxes on an outside wall. If you have room for several layers its a practical solution. Steel plate is also used to shield adjacent areas from magnetic fields generated in MRI imaging.
I noticed you have a shielding around your Argus CRT Steve did you make it your self ?
Hi Harry,
This is a mu-metal shield originally manufactured for VCR97-style tubes. However, at one time I painted it with Hammerite, which later I removed. Getting the Hammerite off was difficult, involving some serious scraping, and I later learned that mechanical shock can reduce mu-metal's permeable properties... as is also stated in your reference material.
I built the Argus back in 1990, but construction was interrupted by a back-packing trip round Asia, including a stint up the east coast of your lovely country from Sydney to Cairns then across to Darwin. It was a great trip but what was I really dreaming about all that time...? You guessed it - the Argus!
I couldn't wait to get back and finish it.
Steve O