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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: EM radiationPosted by anthony on: 4/17/2017
 Paul S wrote:
Anthony, it sounds like you have given a lot of thought to damping structural vibration.  I was referring to the electro-magnetic fields thrown by transformers, and - based on my view of your perspective drawings -  I was wondering if you had also taken steps to isolate tubes from this EMF?


Best regards,
Paul S

Hi Paul,

Well, I feel that the largest step is getting the power supplies and chokes in a separate steel chassis away from the amplifier itself.  How far away depends on the length of the cables I construct.  When I discussed this with Lucas, the guy that wound nearly all my iron, he advised that there will be a significant EM field particularly in the power supply, but that it should mostly be taken care of by using a steel skinned chassis for both the power supply and amplifier and also by separation between the two boxes.

Inside the amplifier itself the only iron is in the filter chokes and output transformers.  The filter chokes are potted into heavy steel cases making them quite well shielded.  The filter for the Raal HF channel has two air caps and two shielded inductors inside a RFI screened box which sits again inside a steel sarcophagus just to be cautious...I remember reading about how much trouble unshielded filter chokes and air-caps gave Romy so I have been particularly pedantic in my situation.

The OPTs, as previously mentioned, have large physical separations from anything with which to magnetically couple.  The best that I could do regarding the RF and EM fields is physical separation.  I did design up a case that had each OPT sitting in its own steel box but in the end I was worried about heat and canned that thought and just went with a larger case and more physical separation.  Is it enough?  I think so and I hope so.  Lucas advised me to keep the Bass OPT at least 50mm from anything, so I have kept it 75mm from anything.

As for specifically shielding the tubes from internal EM radiation, I have taken no steps apart from separation.  Is there anything in particular that you think I should be looking at doing Paul?

Anthony

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