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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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1st Jul 2019, 10:07 pm | #1 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,167
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Replacing a ceramic spindle
The ceramic spindle of a four gang variable capacitor is broken.
It is part of a Marconi passive preselector for use with HF receivers. The length of the spindle is about 200mm and the diameter is approximately 11mm. I assume that a replacement ceramic spindle will be costly and rare. Since it will only be used personally, I want an economic repair. I can buy a Delrin (POM Acetal) rod which I believe is one of the more rigid plastics. A glass rod is another option. Has anyone attempted a repair like this? Do you have any better suggestions? |
1st Jul 2019, 11:13 pm | #2 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,899
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Re: Replacing a ceramic spindle
I think I have one.
I built a preselector some time ago and obtained a rather nice 4-gang capacitor. My circuit design needs all four rotors earthed, so it made sense to turn up a brass shaft for it. So the ceramic shaft may be left lurking in a drawer somewhere. I'll have a look when I have some time. I think a number of these capacitors came on the market in the mid 80's. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
1st Jul 2019, 11:46 pm | #3 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,167
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Re: Replacing a ceramic spindle
The four rotors in this variable capacitor are all wired to chassis. Maybe a steel or brass spindle would be just as good, for my needs.
I initially assumed that they used a ceramic spindle to electrically isolate the rotors. However there may be other advantages such as thermal stability. Some ceramics are 70% more rigid than steel. Perhaps it is the material of choice for the perfectionist. |
9th Jul 2019, 4:09 am | #4 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,899
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Re: Replacing a ceramic spindle
I've had a search..
I still think I've got one rolling around, somewhere. What I have found, is an entire capacitor. 4 sections, big ceramic shaft. David
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
9th Jul 2019, 10:37 am | #5 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,398
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Re: Replacing a ceramic spindle
I wonder if these were B40 spares- I'd heard that it wasn't so unusual to find that the gang capacitor shafts were broken, probably not helped by cramped below-decks situations, brusque handling and considerable weight! If there was noticeable attrition, perhaps stock-holding was generous in the way that there used to be plenty of NOS AR88 output transformers around- until there weren't...
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