Re: Topband: Submerging variable caps in oil as substitute for vacuum variables
The author points out (correctly) the tempco issues with oil dielectric. Still I am intrigued by the thought of a remote tuning capacitor via hydraulic tubing :-). The capacitor plates could be as simple as two concentric cylinder conductors with appropriate spacers. I betcha crud collecting on the top of the oil would set voltage limit. Tim N3QE - Original Message - From: Pete Smith N4ZR [mailto:n...@contesting.com] Sent: Wednesday, January 29, 2014 05:42 PM To: topband@contesting.com topband@contesting.com Subject: Topband: Submerging variable caps in oil as substitute for vacuum variables The omega match for my shunt fed tower uses two 300 uF roughly 3000-volt variables I bought from Henry radio a few years ago. I think occasionally about running more than 100 watts on 160, but the cost of the vacuum variables is a real issue. February QST has an article on using mineral oil immersion to increase the voltage capability of variables in a 600M amplifier. The article does not include any hi-pot data, but indicates that the maximum capacitance went up a lot. Opinions? -- 73, Pete N4ZR Check out the Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com. For spots, please go to your favorite ARC V6 or VE7CC DX cluster node. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Submerging variable caps in oil as substitute for vacuum variables
Subject:Re: Topband: Submerging variable caps in oil as substitute for vacuum variables The author points out (correctly) the tempco issues with oil dielectric. Still I am intrigued by the thought of a remote tuning capacitor via hydraulic tubing :-). The capacitor plates could be as simple as two concentric cylinder conductors with appropriate spacers. I betcha crud collecting on the top of the oil would set voltage limit. Tim N3QE - The omega match for my shunt fed tower uses two 300 uF roughly 3000-volt variables I bought from Henry radio a few years ago. I think occasionally about running more than 100 watts on 160, but the cost of the vacuum variables is a real issue. February QST has an article on using mineral oil immersion to increase the voltage capability of variables in a 600M amplifier. The article does not include any hi-pot data, but indicates that the maximum capacitance went up a lot. Opinions? Tim, I have an oil filled variable capacitor that I picked up surplus many years ago. The spacing is about 0.01 inch, capacitance 1000 pF and if I remember correctly it hi-potted to around 5kV. I still have it. I am using 2 X 500pF @ 7.5kV vacuum variables in my Omega Shunt feed. I normally run 1500 watts out on 160. Top loaded 80 feet of Rohn 45G. Guyed with 6700 lb Phillystran. 73 de Price W0RI and Club Station W0CKC _ Topband Reflector Archives - http://www.contesting.com/_topband