2 models are for tuning with a variable capacitor of the plastic-film type. The other 2 models use varactor-diodes for tuning. The tuning-boxes are designed for greatest versatility, highest Q-factor and sensitive frequency tuning. The signal from the resulting resonant LC- or tank-circuit is buffered with a JFET so that the Q-factor of the LC-circuit is not diminished (only 10 Mohm load-resistance to the LC-circuit). Input-connection is with high-quality binding-posts that also accept 4mm banana-plugs with 19mm spacing. Output-connection is with 4mm banana jacks or with a BNC-connector.