[time-nuts] Spectracom 8170 -> SWCC clock
lists at rtty.us
Sun Jan 22 19:05:05 EST 2012
6K is about right. The resistor was typically a big ceramic wire wound 10K variable.
No guarantee it's right for a clock, just that it's right for a teletype.
On Jan 22, 2012, at 5:46 PM, Jim Hickstein <jxh at jxh.com> wrote:
> On 2012/01/22 15:29, Bob Camp wrote:
>> Teletype loop current as in 20 ma through the coil via a dropping resistor off of 125 vdc.
> Value for the dropping resistor? (I know, I'm an Extra, and I used to design digital circuits, so I should know this stuff. But I've been in software for a long time. Let's see.... E over I R.)
> I measured the setting coil at the terminals: 11.5 ohms. To limit 125 VDC to 20mA, this would need an additional 6.2 Kohms. I suppose that represents the metallic circuit back to WU plus a bunch of other 11.5-ohm clocks on the same circuit, plus a compensating resistor back at the head end?
> Locally, a D cell (or 3 in series, which I have), with about 200 more ohms, might do. (Reaches into desk drawer.) Let's see if I still have that bunch of 100-ohm resistors left over from making an ISDN terminator. Why, yes! Quarter-watt. P over I E. 90mW. Eh, it probably won't blow up.
> I tried measuring the winding coil, too: 0.1 ohms, but I'm not sure I was getting it in the right place. And now I've put the face back on the clock. Otherwise I couldn't tell what time it was! I am really trained to look at that spot on the wall for this information. While the SWCC was in the hospital (for over a year) I had to buy another clock to put there. The blank spot was driving me crazy.
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