From: jl@glen--canyon.com   
      
   On Mon, 26 Jan 2026 13:12:21 -0500, Phil Hobbs   
    wrote:   
      
   >On 2026-01-26 11:48, john larkin wrote:   
   >> On Tue, 27 Jan 2026 03:36:36 +1100, Bill Sloman    
   >> wrote:   
   >>   
   >>> On 27/01/2026 2:53 am, john larkin wrote:   
   >>>> On Sun, 25 Jan 2026 22:44:02 -0500, legg  wrote:   
   >>>>   
   >>>>> On Sun, 25 Jan 2026 08:08:48 -0800, john larkin    
   >>>>> wrote:   
   >>>>>   
   >>>>>> On Sun, 25 Jan 2026 08:51:24 -0500, legg  wrote:   
   >>>>>>   
   >>>>>>> On Sat, 24 Jan 2026 19:25:35 +0000, liz@poppyrecords.invalid.invalid   
   >>>>>>> (Liz Tuddenham) wrote:   
   >>>>>>>   
   >>>>>    
   >>>>>>> In applications where power levels are important, pot core orientation   
   >>>>>>> will affect 'N' in the flux density concentration, and produce early   
   >>>>>>> saturation at the location where minimum x-sectional area occurs.   
   >>>>>>>   
   >>>>>>> RL   
   >>>>>>   
   >>>>>> That should have a small effect on my pulser. Ill try it.   
   >>>>>>   
   >>>>>> I got a 2% change in inductance when I rotated the core halves.   
   >>>>>>   
   >>>>>>   
   >>>>>> John Larkin   
   >>>>>> Highland Tech Glen Canyon Design Center   
   >>>>>> Lunatic Fringe Electronics   
   >>>>>   
   >>>>> 2% FREE x-sectional area, and an indication that the previous   
   >>>>> misalignment doesn't dominate minimum value.   
   >>>>>   
   >>>>> Mind you, you can get a similar change just by forcing out   
   >>>>> the fluff and detritus present at the contacting surfaces.   
   >>>>> That might be what you're actually seeing, even if the core   
   >>>>> is gapped.   
   >>>>>   
   >>>>> In pot cores, minimum x-section usually occurs where the centre   
   >>>>> core meets the top and bottom plates. In parts shapes designed   
   >>>>> for power applications, this is usually corrected.   
   >>>>>   
   >>>>> This core rotation can be used as a tolerance trim, where   
   >>>>> needed, but anything like that before impregnation is probably   
   >>>>> just biting fart bubbles.   
   >>>>   
   >>>> Impregnation?   
   >>>   
   >>> Some people like to lock the windings and the leads in place with a   
   >>> heavy layer of encapsulant. This works better if you put the part to   
   >>> encapsulated under vacuum before you pour on the encapsulant.   
   >>>   
   >>> I've never seen it done, but I've heard about it. It's apparently very   
   >>> messy.   
   >>   
   >> Wet stuff is messy, really nasty in production. In the case of a   
   >> txline transformer made with a few turns of coax, there's no reason to   
   >> pot it.   
   >>   
   >> We just spin a few turns on a bobbin and clamp it into the pot core.   
   >> If it got sloppy, a tie-wrap would secure things.   
   >>   
   >> Some people like the idea of potting things. Weird.   
   >   
   >Last year we did a TDR that had to survive being pounded into hardpan   
   >with a slide hammer (>20k gees).  Potting was the right answer there!   
   >   
   >We put in small bits of foam sticky tape to keep the epoxy from trashing   
   >the pulse shapes.  If we did it again, we'd probably go to a six-layer   
   >board and use stripline to avoid the problem (mostly).   
   >   
   >Cheers   
   >   
   >Phil Hobbs   
      
   Hard-cure epoxy can crush and destroy parts too. And, I've heard,   
   wreck opamp offsets.   
      
   JLC does cheap 6-layers.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
   --- SoupGate-Win32 v1.05   
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