Used to be a member of this forum a few years back, and have just re-joined, and this is my first post.
I have hunted online on Ebay etc for decent air spaced tuning capacitors and apart from used ones there seems very little available.
Has anybody had luck with suppliers of new ones at reasonable prices? (for use on receivers)
As I am now retired and have time available, I am seriously thinking of constructing one, as I have good access to CNC and metalwork machinery. Just wandered if anyone has tried to construct one?
The rest of the parts have now been designed on Autocad. Below is the rendered 3D view from Autocad, as below:
The 2 bases, front and back will be cut from Acrylic sheet (6 or 8mm thick) and the spacer supports (brown) from 3mm acrylic. (the supports will need to be cut on a laser CNC due to the narrow slots, and the rest of the parts can be cut on a router CNC.
The overall size of the tuning capacitor will not be as compact as the smallest air spaced capacitors available, but should still be acceptable for most purposes. The air gap between vanes will be about 0.5 mm
After looking at some tuning dials for medium waves (old ones) I noticed that nearly all
were marked in meters which were equally spaced.
The following article describes the way to calculate the vane shape required
From this I calculated the shape required below would satisfy the linear wavelength type
The next step to cut this in thin sheet aluminum and work out the other parts needed
I have gotten some good caps from Oren Elliott Products:
Some of their models (the ones ending in "P") come with a 6:1 planetary reduction drive built in, which can be very handy for a receiver or tuned loop -- the half-turn movement of the plates gets spread out over 3 full turns of the knob.
When I last ordered, many of their S2 caps also came with optional trimmers; it's a good idea to email them to check / specify which options you prefer (and which ones happen to be in stock in hobbyist quantities).
From their product listing you can see that the prices drop sharply if you can buy at least 2 units, and even more sharply if you can spring for 5 (but that's a lot of projects for me).
One question does any one know, do normal air spaced tuning capacitors for say MW band have a straight line frequency or a straight line wavelength property.
I noticed nearly all of them do not have plain semi-circular plate but have offset centre with oval shape vanes.
Greg, Thanks for Joining !!! "Mikes Electronics Parts" is a deceptively simple retailer of some cool stuff, kind of deep in the site. There are caps that are specially made and the Poly Variable Capacitor Dual 335pf and 20pf is two in one. It is really well made. In fact, it is custom made for Mikes. He also has some really nice metal ones with gearing. For AM radio, he has a special litz wire that is really unbelievably good.
Hope that helps. There are some great articles here. Great people. I plan on expanding the site even more. Thanks again. - Larry