The LC31 and LC31L 3.1 MHz Link Couplers for Plasma Tubes
LC31S coupler with TCS coaxial capacitor.
From left to tight, LC31S, coaxial capacitors type TCP (blue,) TCS (green) and LC31 coil assembly
LC31L-BAT coupler
The LC series of plasma tube couplers has been specially designed to work with all Spectrotek amplifiers and Bill Cheb plasma tubes.
The use of an LC31 coupler is required when using any plasma tube with any of our amplifiers.
Using an LC31 or LC31L coupler allows you to to efficiently feed RF power to your plasma tube while maintaining excellent signal quality.
If you want to know more about the LC31 couplers and how they were designed, here are links to two 2012 web pages that detail the history, design and construction of the first LC31 coupler.
The theory behind the LC31 coupler
Coupler Overview
As you can see from the photos, there are two versions of the LC31 coupler.
The earlier version is the LC31. This coupler uses a white PVC coil form. It was designed to work with all of Bill Cheb's plasma tubes. Please note that when operating at power levels above 200 watts peak or 100 watts average power, it is necessary to use a cooling fan to prevent the windings of the coupler from overheating and softening or melting the PVC coil form. Additionally. when using the LC31 coupler with some plasma tubes, it is necessary to connect a type TC coaxial tuning capacitor across the secondary winding of the LC31 coupler to obtain the correct frequency resonance for proper operation.
The later version of the LC31 coupler is the LC31L. This version coupler uses a clear coil form made of heat resistant Lexan plastic. The LC31L is much more resistant to heat damage. The use of the Lexan coil form combined with an open primary winding results if much less heating of the coupler when it is in operation. Normally, the LC31L coupler does not require fan cooling even at high power levels unless the system is tightly enclosed or if the ambient temperature exceeds about 95F or 35C. The LC31L was designed for operation with Bill Cheb's high power capable tubes, however it will also work with most of his lower power plasma tubes.
Installation
Using either the LC31 or the LC31L is the same. Simply connect one end of a 23 foot or 7 meter length of 50 ohm solid dielectric coaxial cable to the RF OUT connection of any of our amplifiers. Connect the other end of the coaxial cable to the input terminals of the LC coupler assembly. Next, connect two insulated wires from the output terminals of the coupler to the electrodes of your plasma tube. That's it! Now, power up your system. No tuning is required.
LC31, LC31L Construction
LC31
The secondary coil which connects directly to the plasma tube electrodes is wound on a PVC plastic coil form using heavy-enamel insulated 18 AWG copper wire. A primary winding of 14 AWG PVC insulated wire is then wound close spaced over the center of the secondary coil. When the coupler is in use, the primary winding will be connected to the RF output of the amplifier through the coaxial cable mentioned above.
A high voltage Mica RF capacitor is connected in series with the primary winding. This capacitor tunes the primary winding for maximum power transfer for the selected plasma tube. A type TC high voltage coaxial capacitor may be required to be connected across the terminals of the secondary coil winding depending on the particular plasma tube. This capacitor tunes the secondary coil to match your plasma tube. Should you decide to use a different plasma tube, the coaxial tuning capacitor may be easily removed and replaced with a different one.LC31L
The construction of the LC31L is basically the same as the earlier LC31 coupler. The differences are: the use of a Lexan plastic coil form instead of PVC plastic; the use of 12AWG wire instead of 14AWG wire for the primary coil, and; wide spacing of the turns of the primary coil instead of a close spaced primary winding. The LC31L coupler was designed to work without the need for connecting a TC coaxial capacitor across the secondary winding of the coupler.
>> Note that the
price of the LC31 or the LC31L coupler is the same.
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When ordering any LC31 coupler. please be sure to send us an email or place a note on your order and let us know exactly which plasma tube you will be using so that we can be sure to send you the right coupler for your plasma tube
Please refer to the instruction manual for further details.
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