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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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13th Sep 2021, 6:05 pm | #1 |
Octode
Join Date: May 2017
Location: St Austell, Cornwall, UK.
Posts: 1,018
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Strange Pre-set Capacitor
Another odd componant, at least for me!
Can anybody tell me anything about this strange pre-set Capacitior? Not seen one like this before. I had assumed it was an odd connector for the wiring loom, but finaly I realized it was the Pre-set Variable Capacitor I was looking for on the Schematic. Are these Factory pre-set and fixed, or can they be re-adjusted? There are no markings on it, but the Schematic suggests it's 3-30mmfd. I have mearsured it at around 10.77 nF Is mmfd nF or pF ? Thanks in advanced for any enlightenment! Ian |
13th Sep 2021, 6:12 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: Strange Pre-set Capacitor
Is it in a Philips radio??
The basic idea is a tube with a wire up the centre and fine wire wound over the outside. You adjust it by unwinding turns of the fine wire. A commercially rendered version of the twisted wire ' gimmick ' capacitor. Last edited by G6Tanuki; 13th Sep 2021 at 6:19 pm. |
13th Sep 2021, 6:18 pm | #3 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Strange Pre-set Capacitor
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13th Sep 2021, 6:29 pm | #4 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: Strange Pre-set Capacitor
Trombone trimmer. Similar principle to the piston trimmer, but more often seen in low-cost applications, I've seen a few in radio front ends and test-gear compensation, sometimes there's a simple friction lock with a couple of brass ears to squeeze to release it.
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13th Sep 2021, 7:12 pm | #5 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Strange Pre-set Capacitor
Piston trimmer also seen in Philips sets from early 30's but that doesn't narrow it down much as Philips changed their trimmer type every couple of years.
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13th Sep 2021, 7:19 pm | #6 |
Hexode
Join Date: Mar 2008
Location: Bristol, UK.
Posts: 388
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Re: Strange Pre-set Capacitor
This is in the Avo test bridge,probably used to pad a cap used in the lower capacity range.Les
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13th Sep 2021, 8:37 pm | #7 |
Octode
Join Date: May 2017
Location: St Austell, Cornwall, UK.
Posts: 1,018
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Re: Strange Pre-set Capacitor
Thanks for the replies.
Well, I have to say, on closer inspection, it does indeed appear to have a very Fine winding round the outside. Who would have known? Apart from everybody except me by the looks of it! Almost invisible if I hadn't been drawn to looking closely (under a Magnifiying Glass) by Post #2. It looked like just a Brass Tube! Yes, Les, it is indeed an Avo Test Bridge, the subject of my other Thread, and Yes it appears to Pad C1 (85pF) in the Lower Capacitance Range. I assume it is there to get the 85 pF 5% Capacitor to within 0.5% as specified on the Schematic. I thought the 0.5% Tolerance was a bit optimistic! Actually, I thought it was a Typo! If mmfd is pF, then I guess it is way out of Spec at 10.77 nF! So it will need changing out like the rest of the Caps. Not surprisingly, pretty much all the Caps are well out of Spec, but most the Resisters are still in. If it's a Cheap and cheerful componant as suggested, it's a bit of a surprise Avo would have used it in such an Instrument. Ian |
13th Sep 2021, 8:56 pm | #8 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Strange Pre-set Capacitor
Quote:
Lawrence. |
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13th Sep 2021, 9:03 pm | #9 |
Octode
Join Date: May 2017
Location: St Austell, Cornwall, UK.
Posts: 1,018
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Re: Strange Pre-set Capacitor
Now that definately makes more sense now you come to mention it!
Ian |