One of my favorite Grid Dip Oscillators (GDO) is the
Lafayette Grid Dip Meter 99-2503 also known as TE-57.
It has a Vacuum tube oscillator: Nuvistor 6CW4, real 'grid-dip'.
Standard 6-coil Frequency Range: 1.7 MHz to 180 MHz,
Diode Detector mode,
Phone jack for monitoring.
Compact size, sturdy construction,
Tone Modulation, Low power draw <3W.,
uses Standard FT-243 Crystal socket for plug-in coils compatible with several other GDOs (G-30, DM-81, DM-4061, LDM-815, ...),
the Frequency range extends with other coils:
I have used the UHF coil from a Knight G-30 and one TE-57 tuned up to 268MHz and the other to >270MHz.
I have extended the range down to 740KHz(DM-81 A-coil), and lower with large coils.
Drawback: 120VAC power, but it runs nicely on a pocket size 20 watt battery powered inverter by Black & Decker - Vector Products CPI20B/CP120B.