An electron-nuclear double resonance spectrometer to study the Overhauser effect at magnetic fields near 30 G and over a wide temperature range is described. A combination of high Q in the electron resonance cavity with sensitive nuclear resonance detection makes observations on high dielectric loss samples practical. Examples of enhanced nuclear resonance sensitivity (for protons, fluorine, lithium and phosphorus nuclei) are given with an application of the apparatus for very accurate measurements of electron spin resonance parameters at low fields.