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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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18th Nov 2019, 12:23 pm | #21 |
Hexode
Join Date: Apr 2007
Location: W Yorks, UK.
Posts: 407
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Re: Here's why can't you find a modern 250K or 500k potentiometer.
There were letters to Wireless World in the 1940s that asked the very same question, and no one had a definitive answer even then. For all we know, some engineer in the distant past simply nudged his slide rule a little too far!
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19th Nov 2019, 4:23 pm | #22 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,764
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Re: Here's why can't you find a modern 250K or 500k potentiometer.
I still don't think any suppliers are able to supply off-the-shelf 250k or 500k log or linear pots with a DPST switch, but Blore Edwards will indeed make them to customer requirements (250K & 500K as well as 220K & 470K) in a wide range of options which can be specified on their order form. (They can also supply reverse log tracks in ten values, though not the 50K needed for the Portadyne Princess. Maybe 100K with 100K resistor in parallel would suffice?). The shaft can be plastic or metal, imperial or metric, in three lengths up to 50mm, with either no flat, or a flat as specified by the customer on the order form, including the depth of the flat and the angle. T(he tracks can handle 1/2 Watt linear, 1/4Watt log).
They can even supply dual concentric pots, with or without swtch. As to the switch options, there are six combinations, which sounds confusing until you look at the diagrams. For example, what we (me anyway!) would consider to be normal double pole on/off switch, is describe as 'OFF-ON OFF-ON'. I'd never thought of it that way, but there are two poles and each pole switches from Off to On. The poles can be in six different combinations, as depicted in the diagram below. All for £7.25 for a single pot - what an outfit! https://www.blore-ed.com/product-pag...er-metal-shaft https://www.blore-ed.com/series45potentiometers So, not quite 'off-the-shelf' - better than that 'made to measure'! Interesting history: https://www.blore-ed.com/history Not a topic for discussion in this thread, but as an aside, I find it fascinating that Blore Edwards is tucked away in Aberdare - a small Welsh town with a population smaller than the village I live in. But then why not? As Spike Milligan once said: 'Everyone has to be somewhere'! https://en.wikipedia.org/wiki/Aberdare
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David. BVWS Member. G-QRP Club member 1339. |
20th Nov 2019, 12:29 am | #23 | |
Nonode
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,944
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Re: Here's why can't you find a modern 250K or 500k potentiometer.
Quote:
Judging by the attached Wireless World 1952 February article, “Why 47” (by Cathode Ray) (see second page, second column) this came about because the rounding was chosen to smooth out the E24 series, with the same numbers then carried over to the E12 and E6 series. There were 8 cases where the actual electronic E24 series departed from the natural series, as shown: “Natural” E24 series rounded to two significant digits: 10, 11, 13, 15, 16, 18, 20, 22, 24, 26, 29, 32, 35, 38, 42, 46, 51, 56, 62, 68, 75, 83, 91, 100 Actual electronic E24 series: 10, 11, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91, 100 Most of the deviations were a case of rounding up (or down) where rounding down (or up) would have been mathematically correct. But 30 and 36 were bigger deviations, the “natural” series numbers, to five significant digits being 28.723 and 34.807. Cheers, |
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21st Nov 2019, 7:16 pm | #24 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Here's why can't you find a modern 250K or 500k potentiometer.
Piher T21 has those in the standard range. Standard multipliers for that series are 1.0 - 2.0 - 2.2 - 2.5 - 4.7 - 5.0 for resistances between 100 ohms an 5 megs. Lin, log, alog. Several switch types to choose from. Other values upon request, though I suppose custom versions might be more expensive than 7.25 pounds when you want only 1 piece.
Last edited by Maarten; 21st Nov 2019 at 7:33 pm. |