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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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16th Nov 2020, 2:46 pm | #1 |
Heptode
Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 612
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How does this vac variable capacitor adjust please?
I am familiar with vac variables that adjust value via a threaded rod that you turn to mesh and unmesh the plates, but I have seen one that I am unsure of the adjustment method.
It looks to me as if the rod was designed not to turn, but to be pulled out, perhaps using a cam as the rod also seems to have a ball or swivel joint inside the body to allow misalignment. Cam used to pull the rod? Motor drive using and external threaded rod and bushing? What might be the hollow tubular stub on the side of the body be for? Can it be used with a conventional panel knob or panel turns counter? It's a 50 to 5000pF at 10kV Comet vac variable, anyone able to shine a light on the designed adjustment method and possibly an ideas as to its age? Part number is CV1A-5000E/10 Many thanks for any insight. I am looking for a 1000pF or greater vac variable, with an operating voltage of over well 5kV if anyone has anything that is, or can be, tested for breakdown. I have a suitable uA HV tester. I'm in north Shropshire.
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Best Regards, CW. 2E0ILY |
16th Nov 2020, 10:26 pm | #2 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
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Re: How does this vac variable capacitor adjust please?
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17th Nov 2020, 11:03 am | #3 | |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: How does this vac variable capacitor adjust please?
Quote:
Because of the vacuum, there's a hell of a lot of torque involved and chocks of wood are used when working on the servo drive so the cap doesn't thunk in and take your finger-ends with it.
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Regds, Russell W. B. G4YLI. |
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17th Nov 2020, 11:58 am | #4 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
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Re: How does this vac variable capacitor adjust please?
The pipe stub will be for forced air cooling of the bellows and of the floating capacitor electrode structure. THe fixed capacitor electrode structure is accessible for conduction cooling at the bottom end of the capacitor (it will be electrically hot, of course)
These things are for 100 to 1000Amps of current. Cooling is important. Water cooled ones can shift more heat but it's messy and two smaller pipe connections are needed. David
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17th Nov 2020, 3:20 pm | #5 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: How does this vac variable capacitor adjust please?
Here's the drive arrangement of a 50-2300pF CV1C-2300FW/15 which looks similar to yours. You can see the shaft attached to the stirrup rising through the deck and the cam, gears and motor that drive it. The configuration (on this transmitter) doesn't use the collar and the cap is bolted directly to the deck.
There is no forced cooling.
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Regds, Russell W. B. G4YLI. Last edited by russell_w_b; 17th Nov 2020 at 3:25 pm. |
17th Nov 2020, 11:21 pm | #6 |
Hexode
Join Date: Mar 2006
Location: Helston, Cornwall, UK.
Posts: 301
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Re: How does this vac variable capacitor adjust please?
What are you building?, it’s going to be impressive...
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18th Nov 2020, 12:49 am | #7 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,527
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Re: How does this vac variable capacitor adjust please?
RF induction heater? Welder?
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18th Nov 2020, 10:37 am | #8 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
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Re: How does this vac variable capacitor adjust please?
Odd that they do not have a standard product that goes to 5000pF so I presume that must be a custom part.
Looking at the pictures, I would say there is a bit missing - clearly it needs some kind of gland at the top which may be where the screw adjuster would be. So maybe it has been taken out of something, so I wonder if it still works. |
18th Nov 2020, 12:25 pm | #9 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,684
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Re: How does this vac variable capacitor adjust please?
What you need is a smaller one of these. It can either sit on the end of your existing collar or right on the cap itself, depending on the length of threaded shaft you have. That said, I suspect your cap has a fixed drive-rod that can't be removed or modified so easily as your rod looks to go down into the cap itself and is secured differently. But it will convert your cap to a rotary-tuned one.
This is an EEV one, but Comet and Jennings ones are similar. As I recall, new caps come with them whether you need one or not.
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Regds, Russell W. B. G4YLI. |