Grid Dip Oscillators


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MIL AN/PRM-10 I personally removed from the MIL wrapping from my AN/PRM-10, new; it is among the best of GDOs (a title shared with the Measurements 59 and Millen 90662 'Industrial' model).

Millen 90652 Solid State GDO My 90652s are both (an original and a Caywood-made unit) Mint-NIB; plus I have several of the 'regular' tube-type 90651 Millens-including one Mint-NIB unit. And a separate set of the VLF-MF coils, in excellent condition, w/data conversion sheet. A recent acquisition is the Industrial model, the 90662. This GDO comes in a special metal case, with the VLF-MF coils, and a built-in tone modulator. Despite describing itself as potentially "battery operated" the 90662 still uses a single 9002 tube as its oscillator-but adds a 2N175 to the 2N406 for the tone modulator and DC meter amplifier, respectively. Finally, I just acquired its predecessor Industrial model: the 90661. Essentially, it's a 90651 with a metal case and the different designation. It has the individually calibrated coils, but no tone modulator or DC meter amp, and no VLF-MF coils. Also part of my collection is Millen 90651 SN:1 and Millen 90662-A SN:15. With the latter 90662-A GDO, I now have every GDO model Millen ever made.

I also have 3 90600 Wavemeter sets-including one that is near-mint, and the Millen 90672 Antenna Bridge w/all 4 coils in excellent condition. An excellent source of Millen information may be found at:  MILLEN . Click on the James Millen MFG banner above, to get to my very incomplete Millen GDOs page-it DOES have both JPG and PDF versions of the LF Coils Frequency Conversion Chart.

Monarch GDM-1 The GDM-1 is another version of the "Midland Tr". Both obviously made by the same manufacturer.


New London Instrument Company Model 200 UHF Grid Dip Oscillator. This unit just showed up on ebay-I had never even heard of it until then.

NOVEX Grid Dip Meter - Model DM-4061 in MINT condition. Frequency range: 1.5 through 250 MHz (Six plug-in coils).  This is the excellent GDO model currently sold by ALFA Electronics (at a VERY good price).

PACO Model G-15; PACO was an EICO competitor, and is similar to the EICO 710.

PEL Electronics  Model DM-201; PEL was a small electronics manufacturer that I believe existed in the early 1960s. This unit has 2 socketed Germanium transistors, and I have all the coils. A very rare unit.

Quemont Electronics GDM-3 Transistorized dip meter with a range of 0.5 to 150 MHz, using 6 plug-in coils. Identical to the Midland/Thoro-Test Series.

Radiometer Copenhagen Model GDO.1b; European made, distributed in Canada, this is a very well made, AC-powered GDO, covering 2 - 220 MHz. Condition of mine is very good-to-excellent.


Savant GDO Model DM-250 is a transistorized dip meter with a 1.5 to 250 MHz range, using 6 plug-in coils. The unit strongly resembles the Lowe FX-1, and-like most solid state GDOs-uses one 9 VDC battery.

Tech model TE-15 is a later model of the Midland/THORO-TEST series of GDOs. It features a three transistor circuit over the one transistor of the original series. Looks practically identical. Click for larger picture.      



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