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Old 27th Jan 2009, 9:49 pm   #21
'LIVEWIRE?'
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Default Re: 470K switched log pots

No specific requirements at the moment, but other types which need replacing from time to time, and which are now (almost?) impossible to obtain in any values, are those with a 'loudness' tap, usually about 30-40% of the total resistance value, and the dual CONCENTRIC type. Even the dual ganged, switched types are hard to come by nowadays.
Incidentally, i have some NOS pots. of various types, including a fair quantity of model-specific Blaupunkt Car radio/Stereo pots, the latter mainly for sets produced from the early 70s to the late 80s. I will have to sort & list them sometime, but if anyone wants such a control, let me know, and I'll check my stock.
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Old 28th Jan 2009, 2:23 pm   #22
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Default Re: 470K switched log pots

Having had endless problems sourcing potentiometers in higher resistance values, particularly dual-gang (stereo) ones, I have resorted to building my own.

Farnell stock a range of imperial size pots (3/8" bush and 1/4" shaft with flat). Single-gang pots (log and lin) without switch go up to 1M. They also stock switched pots and dual-gang pots from the same range, but only in a limited range of values. Sadly, the range does not include pots with tapped tracks or concentric spindles.

It is simply a case of buying a single-gang pot with the resistance value needed, plus any switched or dual-gang pot, and transferring the resistive track(s) over. The pots come apart easily, and the construction is modular, so it should be possible to build up any pattern needed (e.g. dual-gang with switch) provided enough bits are purchased. It seems rather a bodge, but is often the only cost-effective solution for occasional repair jobs.

Single gang: http://uk.farnell.com/jsp/level5/mod...=en/207166.xml
Dual gang: http://uk.farnell.com/jsp/level5/mod...=en/207185.xml
Switched: http://uk.farnell.com/jsp/level5/mod...=en/207414.xml

The downsides are:

Having to purchase more pots than needed, and having unwanted bits left over;
Plastic shafts are a bit wobbly, but at least the flat is the correct shape and extends the full length;
The "diy" pot may end up labelled with the wrong resistance value.

I have attached a couple of photos showing the three styles available, and a dismantled switched pot showing the components.

Hope this helps,

Roy
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Old 28th Jan 2009, 2:28 pm   #23
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Default Re: 470K switched log pots

Roy,
I, too, have done the same quite often in the past, making up pot(s) to suit the job in hand. Dual Concentric types are still a bit difficult, since, of course, you need a couple of concentric types in the first place!
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Old 28th Jan 2009, 2:40 pm   #24
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Default Re: 470K switched log pots

I forgot to mention that the datasheet for these pots does describe a concentric style (type 29) but these are not stocked by Farnell.

However if a supplier could be found, the same approach could probably be used - buy a batch of concentric pots of any value and install the appropriate tracks. Frequently concentric pots have two tracks of differing values anyway (e.g. for volume and tone controls).

The datasheet can be found here:

http://www.farnell.com/datasheets/75268.pdf

Roy
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Old 28th Jan 2009, 2:43 pm   #25
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Default Re: 470K switched log pots

Quote:
Originally Posted by Roy View Post
The downsides are... Having to purchase more pots than needed...
What's the total cost of a switched single-gang pot PLUS an unswitched single-gang pot of the correct value, from Farnell?

Nick.
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Old 28th Jan 2009, 2:47 pm   #26
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Default Re: 470K switched log pots

Nick, the prices vary a bit but average around £1 for the unswitched and £2.50 for the switched and dual-gang versions. They can be purchased singly, which is an advantage.

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Old 28th Jan 2009, 2:49 pm   #27
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Default Re: 470K switched log pots

Thanks Roy. So a little over £4 incl. VAT, with the bonus of a "free" unswitched pot which may be useful for other things
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Old 28th Jan 2009, 7:59 pm   #28
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Default Re: 470K switched log pots

mine arrived today, thankyou, weekend saved
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Old 28th Jan 2009, 11:35 pm   #29
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Default Re: 470K switched log pots

I think Oerjan's post means that everyone's now safely received their pots! Thanks everyone for your payments and also for your kind words both in the thread and via PM.

It's interesting to see, from the links in Roy's post (No. 22), that switched pots can be obtained for as little as £2.50 or thereabouts. Let me just say that the 470K ones cost a LOT more than that - I won't publish the costs here, but if you're burning to know, drop me a PM and be prepared to be surprised.

Finally, I've contacted Mike Barker (BVWS chairman) with a link to this thread and asked whether the BVWS might consider adding switched pots to their 'parts dept'.
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Old 29th Jan 2009, 1:48 pm   #30
Geoff 555
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Default Re: 470K switched log pots

Hi Neil yes the pots arrived safely, thank you very much.
Cheers.
Geoff.
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