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1. [Amps] PTFE dielectricum variable cap (score: 1): Author: "pc5m, Carel" <pc5m@xs4all.nl>; Date: Mon, 15 Mar 2010 21:36:16 +0100; Hi, I would like to get the opinion of this group on constructing a homemade variable 500 pF/1nF capacitor for my new 160mtrs amp. To get sizes down I am considering using 1mm (40 mill) thick teflon; /archives//html/Amps/2010-03/msg00277.html (7,085 bytes)
2. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: TexasRF@aol.com; Date: Mon, 15 Mar 2010 17:03:36 EDT; Carel, dielectric losses in PTFE are many times lower than the dielectric material in ceramic capacitors. Your idea should work just fine electrically. Your challenge will be the mechanical design to; /archives//html/Amps/2010-03/msg00278.html (8,651 bytes)
3. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: Ron Youvan <ka4inm@tampabay.rr.com>; Date: Mon, 15 Mar 2010 17:05:30 -0400; Since "p means 10-12 (million-millionth), so 1000 pF = 1 nF" you are going to build a 500 to 1000 pF capacitor? I would think about putting a 50 pF to 500 pF in parallel with a 470 pF doorknob (or s; /archives//html/Amps/2010-03/msg00279.html (8,268 bytes)
4. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: "la7sl Nils Petter" <la7sl@norgespost.no>; Date: Mon, 15 Mar 2010 22:12:36 +0100; I tried to make a fixed padding (parallell) cap for 160 plate circuit ( PI ) using a stack of brass/ptfe/brass etc connecting together every second layer. It was finally pressed together by means of; /archives//html/Amps/2010-03/msg00280.html (9,674 bytes)
5. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: "la7sl Nils Petter" <la7sl@norgespost.no>; Date: Mon, 15 Mar 2010 22:27:15 +0100; On the other side : I have also used PTFE as dielectricum in the plate coupling cap in a 4CX250B amp with a 1/4 coaxial plate circuit...No problems with that one...on 144 Mhz ! Points toward poor pol; /archives//html/Amps/2010-03/msg00281.html (7,453 bytes)
6. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: ToddRoberts2001@aol.com; Date: Mon, 15 Mar 2010 18:33:11 EDT; Hi, I would like to get the opinion of this group on constructing a homemade variable 500 pF/1nF capacitor for my new 160mtrs amp. To get sizes down I am considering using 1mm (40 mill) thick teflon; /archives//html/Amps/2010-03/msg00282.html (9,236 bytes)
7. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: "Dr. David Kirkby" <david.kirkby@onetel.net>; Date: Mon, 15 Mar 2010 22:41:07 +0000; I'd double-check the relative permittivity of PTFE - I don't think it is as high as 10. I don't say this reference can be trusted, but http://www.microwaves101.com/encyclopedia/permittivity.cfm says; /archives//html/Amps/2010-03/msg00283.html (8,645 bytes)
8. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: TexasRF@aol.com; Date: Mon, 15 Mar 2010 18:42:36 EDT; Teflon is rated for 1500 kv per inch. .040 thickness is good for 60,000 volts! You can find the info at google "teflon voltage". A typical application is for a plate bypass at VHF or UHF where 5 to 1; /archives//html/Amps/2010-03/msg00284.html (9,845 bytes)
9. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: TexasRF@aol.com; Date: Mon, 15 Mar 2010 18:45:30 EDT; You are right Dave, the dielectric constant is about 2.3. But, you can use much closer plate to plate spacing and that will increase the total C many times. 73, Gerald K5GW In a message dated 3/15/20; /archives//html/Amps/2010-03/msg00285.html (8,617 bytes)
10. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: "DF3KV" <df3kv@t-online.de>; Date: Tue, 16 Mar 2010 00:20:34 +0100; That will work pretty well. The loading capacitor in the Tentec Titan 425 is made that way. There is also a relatively small 3nF unit available in The Netherlands which I bought them for amplifier pr; /archives//html/Amps/2010-03/msg00286.html (9,497 bytes)
11. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: "pfizenmayer" <pfizenmayer2@q.com>; Date: Mon, 15 Mar 2010 17:08:44 -0700; What I wonder about is having small air gaps at spots where the teflon sheet and the rotor/stator plates are bearing against the teflon. If the dielectric is uniform there is no problem but it seems; /archives//html/Amps/2010-03/msg00287.html (12,690 bytes)
12. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: ToddRoberts2001@aol.com; Date: Mon, 15 Mar 2010 20:19:49 EDT; Teflon is rated for 1500 kv per inch. .040 thickness is good for 60,000 volts! You can find the info at google "teflon voltage". A typical application is for a plate bypass at VHF or UHF where 5 to 1; /archives//html/Amps/2010-03/msg00288.html (9,512 bytes)
13. [Amps] PTFE dielectricum variable cap (score: 1): Author: "herzog@frontiernet.net@frontiernet.net" <herzog@frontiernet.net>; Date: Mon, 15 Mar 2010 23:06:02 -0400; this can not work UNLESS you find a way to exclude the air from the capacitor plates. ANYTHING you place in between the plates will increase the electric field strength. I found that oil worked, but; /archives//html/Amps/2010-03/msg00291.html (6,909 bytes)
14. Re: [Amps] PTFE dielectricum variable cap (score: 1): Author: donroden@hiwaay.net; Date: Tue, 16 Mar 2010 08:41:31 -0500; http://www2.dupont.com/Kapton/en_US/ Don WA4NPL _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps; /archives//html/Amps/2010-03/msg00296.html (8,111 bytes)
15. [Amps] PTFE dielectricum variable cap (score: 1): Author: "pc5m, Carel" <pc5m@xs4all.nl>; Date: Tue, 16 Mar 2010 23:10:02 +0100; First of all, thanks a lot for all contributions so far ! Seems to be a fun project to take on : - ) One thing I did in the meantime was to calculate/check the field strength in the airgaps which wil; /archives//html/Amps/2010-03/msg00313.html (10,097 bytes)

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