Millen 90651 Grid Dip Meter

© Brooke Clarke, N6GCE


Millen 90651 Qtr View
Coil Set in Bench Rack
Millen 90651 Top
Millen 90651 Back Coil Socket

Background

The Grid Dip Meter aka Grid Dip Oscillator uses a meter in the grid circuit of a tube to sense the loading on oscillator tank circuit.  When the frequency of oscillation is adjusted to that of a nearby tuned circuit the grid current dips, hence the name. Since it is both a signal generator and a signal detector it can be used in many applications.

This Grid-Dip Meter can be used with it's line cord, or batteries (6 Volt A and 67 to 135 Volt B) can be used for power.  There is a Plate Voltage switch on the front panel so that the oscillator function can be turned off so the tube can be used as a detector.

The line cord on this unit appears to have never been undone and the small paper UL tag is still on the cord..  Maybe this is a New Old Stock unit? 

Ranges

Band
Start
Mc
Stop
Mc
Color
A
1.7
4.5
Brown
B
2.9
7.5
Red
C
6.4
16
Orange
D
13
32
Yellow
E
25
60
Green
F
60
150
Blue
G
140
300
Violet
Coil Log
0
10
-

Manual

The manual has a number of applications for Grid-Dip Meters in general.  The topics covered are:

Section I General

  • Grid-Dip Oscillator
  • Oscillating Detector 0 use external headphones with 1/4" mono plug
  • Signal Generator
  • Tuned R.F. Diode or Non-Oscillating Detector - Plate turned off

Section II Methods of Coupling

Figure 1 has a number of cases.

Section III Applications

  • Receiver Tuned Circuits
  • Transmitter Tuned Circuits
  • Neutralization
  • Parasitic Oscillations
  • Parallel Reasonant Traps
  • Series Reasonant Traps
  • R.F. Chokes
  • Measure Circuit Q
  • Relative Q at given frequency
  • Measurement of Capactance
  • Measurement of Inductance of R.F. Coils
  • Relative Q of Capacitors or Inductors
  • Antennas
  • Tuned Reasonant Feeders, as used in Zepp Antenna
  • Untuned or Non-reasonant Feeders
  • Tuning the Parasitic Beam
  • Quarter-Wave Shorted Lines
  • Quarter-wave Open Lines
  • Half-wave Shorted Lines
  • Half-Wave Open Lines
  • Check Standing Waves
  • Relative Field-strength Meter

Section IV Power Supply

Has information on how to connect batteries.

Section V Ground

The 90661 has a 3-wire power cord, but the 90651 has a 2 prong A.C. cord.

Section VI Maintenance

Has some minimal troubleshooting information.  But remember that the circuit is also minimal.

Section VII Low Frequency Use

Lists the optional coils for 325 kc to 2,000 kc.

Section VIII Coils

Seven coils are standard and cover 1.7 to 300 Mc.
Note: You can make your own coils and a couple of 6-32 screws will fit into the coil sockets.

Section IX Technical Summary

Basic specifications.

Schematic Diagram

Capacitor Test Fixutre & Equations

Graph showing Dial reading vs. Frequency for Low Frequency Coils

Capactance Calibration Graph

Parts List

Order

Manual as 21 page pdf document with 4 photos added to end. The text has been OCRed and appears as text, not images, making it much easier to read.  Can be printed on 8.5x11" paper.
The origional manual was stapled at the top and then folded into an 5 ½ x 8 ½ size.
See the product page for ordering information.


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page created 10 Oct 2003.