From: jl@glen--canyon.com   
      
   On Mon, 26 Jan 2026 10:50:30 -0500, 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?   
   >   
   >For semiconductors, you'd get away with slug tuned 'can' - still   
   >candidate for a varactor.   
   >   
   >Lots of headaches with pot cores - mounting, termination etc. The   
   >smaller parts actually increased in price . . . .   
   >   
   >RL   
      
   I've designed passive bandpass filters with adjustable pot cores.   
   There are times when they make sense.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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