We l l l l l l . . . . in still not having had a comeback from THE post initiator .
I will just say that I would take the now assumed to be 679,700 ohm 1 % ree-sistor and tie a 300 ohm in series and go fer it. Then, seeing how close I would come to that all magical 680K final result.
In having been around for long enough time and in different manufacturing environs.
I would never have seen that loose 25% spec used, but only as bad as 20 % on the manufacturing of CARBON COMPOSITION resistors.
In that process, the basic carbon slurry has to be created and then doctored with a mix in of graphite/or/ carbon and conductive metallic dust or inert silica dust filler, to acquire the desired resistance value being shot for, being within an accomplished / mandated specific molded resistor pellets size.
Then there has to be the consideration of compression within the molds forming stage and the final molding to the lead wires and the final heat curing.
That involved manuf process all ends up . . .hopefully . . . somewhat close to the desired end resistance.
In actuality, that is the point where the sorting of each unit and measuring resistance and assigning its actual value to the then blank outer bakelite cylinder, where it then receives its sets of color rings for identification.
The most impressive resistors I remember having seen being made were the early day carbon and metal film units that were made by "Tejas Instrumentations" for military and aerospace applications.
They used gaseous diffusion and a vacuum deposition of a sputtered metal alloy film on a high-grade ceramic rod.
The finished rods resistance would typically be about 1/3 of the final desired resistance.
The resistance was adjusted to final value by a helical laser cut in the metallized resistive film, the resistor would be spinning and a micro precise stepper motor would rapidly divide the element in 1/3's until that final slow down with micro-movements and a reduction of the laser output down to single pulses of resistance trimming adjustment , then a dump of the resistor and the start of another.
The standard run was for 1% units, with some runs for .05% or .01% values of precision, where they would use 5 spirals of division. Then there were special order runs, where they stepped up the spirals to 10 dividing spirals.
That then let them make their .005% and .001% precision values.
The thing of beauty then, was their enclosing the units within a hermetically sealed glass ( it, seeming almost of Pyrex quality) bonded case.
Imagine the standard 1N914 or 4148 cases, which you are familiar with, and then the mentioned units above, being the larger dimension of a 1/2 watt carbon composition resistors case sizing.
The best I ever saw any other manufacturing firms doing was the mere loose enclosing of their resistors within a clear plastic sleeve. No closed hermetic seal was being involved at all, much less the gold flashed leads that the TI units additionally provided.
Thassssit . . . . .
73's de Edd
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