[Elecraft] Hum Coupling

[Jim Wiley]

This belongs in the For What Its Worth file:


I cannot help but note that the venerable Kenwood TS-930S and TS-940S 
rigs had their big hunk of a power transformer mounted right next to the 
PLL section - and no hum problems were apparent, and it was NOT a 
toroidal type transformer, just a standard E+I section type, with no 
outer cover - you could see the laminations and windings. 


Yes, the PLL assemblies were inside shielded compartments, but there did 
not appear to be anything special about them - specifically, they were 
not "Mu Metal", although they were steel.  However, the radio would 
operate just fine when the shield covers were open - as during testing 
and alignment, so the shielding or lack thereof  (in the Kenwoods) was 
not germane to that sort of problem.  What was different about their 
design that made it "hum proof" - at least from fields induced by the 
mains transformer?


So, maybe the problem could be worth another look, as in maybe there is 
another way to solve it?  Could something be done to the K2 itself to 
make it immune to this problem?


This needs someone who is a better engineer than me to come up with an 
answer- I am just a lowly self-taught fumbler.


73,  -  Jim, KL7CC
 

Michael Harris wrote:

>G'day,
>
>By coincidence I opened up our stereo amp to have a go at lubricating a 
>noisy volume pot.  I noticed that the torroidal mains transformer was of 
>shielded construction.
>
>Maybe this is the answer to the PSU hum coupling problem.  A 20A psu in a 
>double height EC, speaker etc as has already been suggested.
>
>Regards,
>
>Mike VP8NO 
>
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