Grid Dip Oscillators


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THORO-TEST GDM-3 Ttransistorized dip meter with a range of 0.5 to 150 MHz, using 6 plug-in coils. Identical to the Midland... or perhaps the Midland is identical to it!  Made in Japan, before MC became MHz.


Triplett Frequency Meter Model 3256 (actually it is a single coil wavemeter) one in very good condition, and one in excellent condition.


  • from the Triplett advertisement p115, 1952 ARRL Handbook, 29th Ed.

A band-switching tuned absorption frequency meter that covers 5 Amateur bands. Has Germanium crystal, and a DC Milliameter indicator, for greater sensitivity. Direct calibration on panel-no coils to change. Switching permits instantaneous broadband change. Audio jack provides for monitoring of phone signals-another new feature. Calibration is in megacycles in the following bands: 3.5-4 MC; 7-7.3 MC; 14-14.4 MC; 21-21.5 MC; 28-30 MC. Coil is removable, and other coils may be substituted for special bands. Use for checking: Fundamental frequency of oscillating circuits; Presence, order, and relative amplitude of harmonics; Parasitic oscillations, etc. Size: 7 1/2" x 2 1/2" x 2 1/4". Metal case with gray hammertone enamel finish & black trim.

Trio (Kenwood) DM-801 in good condition-this GDO is either an early version of the Kenwood DM-81, or it is a home-market version with the parent corporation's name. Physically identical except the different mfgr-name and model number.

and finally:

Waters Manufacturing Model 331 GDO This unit is physically and electrically identical to the B&W 331 at the top of this page. Both were known as the "L'il Dipper" and were model "331". This particular unit is as near-MINT as it gets. Beautiful condition. Click on the schematic for full-size:

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