From: bill.sloman@ieee.org   
      
   On 27/01/2026 2:50 am, legg wrote:   
   > On Mon, 26 Jan 2026 17:56:10 +1100, Bill Sloman    
   > wrote:   
   >   
   >> On 26/01/2026 2:44 pm, 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.   
   >>   
   >> There is a way of doing trolerance trims on some gapped pot cores.   
   >>   
   >> The manufactures put cylindrical hole down through the centre of the   
   >> core, and sell an adjustor which plugs  into the hole. There a ferrite   
   >> slug in the adjustor which you can screw up and down to fully or   
   >> completely bridge the the gap between two core halves.   
   >>   
   >> I've used them, and they provide enough adjustment to let you trim out   
   >> the residual tolerance on the inductance of a gapped core which can get   
   >> up to perhaps +/-5%, and a bit more.   
   >>   
   >> The one time when I designed one in to get a precise 15MHz source for TV   
   >> style video, one of my colleague engineers copied the design for a much   
   >> higher volume project, he left out the adjustor - we were also using a   
   >> varactor diode to accomodate the frequency difference between production   
   >> TV displays and he figured that that - one its own - could cope with   
   >> both sources of variation. Varactors are very non-linear, and I was   
   >> worried about getting out of the region where they were linear enough.   
   >>   
   >> Jerry was a very good engineer - if not all that self-confident - and   
   >> I'd been warned off expressing any doubts about his designs, because   
   >> he'd take my doubts much too seriously.   
   >   
   > Pot cores were developed for tube-amplitude cctry. I expect that   
   > adjustible varieties had added cost. How did it compare in cost to   
   >   the addition of a varactor?   
      
   The varactor was there anyway.   
      
   The hole down the middle of the pot core did mean the part was dearer   
   than it's plain vanilla equivalent, and you had to pay extra for the   
   adjustor, but only a few cents. The time for final test to set the   
   adjustor to give the right frequency and fix it there with a blob of wax   
   was probably the most expensive element.   
   > For semiconductors, you'd get away with slug tuned 'can' - still   
   > candidate for a varactor.   
      
   The gapped pot cores were  a more up-market option. There's nothing   
   about pot cores that make them more appropriate for tube-amplitude   
   applications - they tend to be very flexible if you know what you are   
   doing. People who want to buy all their components off the shelf tend to   
   be less aware of this.   
      
   > Lots of headaches with pot cores - mounting, termination etc. The   
   > smaller parts actually increased in price . . . .   
      
   There are lots of headaches with every component. Pot cores need   
   windings, but you can buy a coil former with mounting pins designed to   
   integrate with the pot core. RM cores are sold with pinned mounting   
   clips that you can use to lock the RM-core halves together around the   
   coil former, and you can plug the whole assembly into  a set of tinned   
   holes on your circuit board and wave-solder the lot.   
      
   There are surface mount equivalents, but I've not kept up with them.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)