AVOMINOR and MULTIMINOR AVOMETERS

INFORMATION

This page attempts to provide details of the pocket sized multimeters based upon the design first manufactured in 1933:

By opening individual images on this page in a new window they can usually be viewed at a larger size

Please advise me of any errors or send me images that are missing  or may be of better quality

    DC AvoMinor Introduced 1933

This one in my collection was made in 1938

2mA 2.5 inch moving coil meter
DC 6, 120, 300 volts - sensitivity 3mA
DC 6, 30, 120 mA
R 10kohm (~340 ohm center)

and with external battery:
R 60kohm (on 6V range)
R 1.2megohm (on 120V range)

The battery compartment was designed to take the now obsolete EverReady U10 which is the same size as one of the cells in a 4.5Volt flat cycle lamp battery. An AA cell could be used  with a spacer or modified spring.       

instruction manual here

later models have one piece magnet and stepped sides to Bakelite case.

     

DC AvoMinor introduced 1935

This one in my collection was made in 1946 and were still available in 1950's

Socket added at center of ohms adjuster knob        

2mA 2.5 inch moving coil meter
DC 6, 60, 300 volts - sensitivity 3mA
DC 12, 120, 600 volts - sensitivity 6mA
DC 3, 6, 30, 120 mA
R 10kohm (~340 ohm center)

and with external battery:
R 60kohm (on 6V range)
R 600kohm (on 60V range)
R 3megohms (on 120V range)

             

instruction manual here

 schematics

[open in new window to see full size]



HR minor

DC AvoMinor (High Resistance) introduced 1938

avominorhr.jpg

avominorhr.jpg

Made just before WW2. Not general-purpose

DC 2.5, 10, 25, 100, 250, 1000 volts - sensitivity 50 uA
DC 50, 250 uA

The following is from an advert at the time of its introduction.

A new instrument has been developed of the same size and appearance as the DC AvoMinor, but it is especially suitable for the direct measurement of grid bias and television voltages and currents. In its essentials, it is an extremely sensitive DC micrometer calibrated as a multi-range Voltmeter and megohm meter. As a voltmeter, all six ranges are of 20,000 ohms per volt which corresponds to 50 microamp consumption at full scale deflection. For resistance measurement an external source of DC voltage is required, the scale being calibrated for use with the 10-volt socket,while adjustment is provided for the actual voltage employed. If 100 volts is applied to the appropriate socket, the resistance scale should be multiplied by 10.

size:102x76x44mm

Cost £3.10s

I am indebted to Dave Philpott for these images of his 1938 meter.


low ohmmeter

AVO low resistance ohmmeter

more information here


ow ohmmeter

I am indebted to Dave Philpott for these images of his 1941 meter.


Universal Avominor  Model 1  (22 range)

Introduced about 1934


avominor

This model has a 1500V range but no 250V range

   

   later design

 These two in my collection were made in 1935 and 1946, they continued to be made into the 1950's.


From 1952 advert

You will find a copy of the avominor-instruction booklet here (large pdf file)

DC 5, 25, 100, 250, 500 volts - sensitivity 2.5
DC 2.5, 5, 25, 100, 500 mA
AC 5, 25, 100, 250, 500 volts - sensitivity 2.5 mA
Non-linear scale for 5 volts
R 20k ohm (400 ohm center)
(Some had 500, 1500 volt ranges instead of 250, 500)

The battery compartment was designed to take the now obsolete EverReady U10 which is the same size as one of the cells in a 4.5Volt flat cycle lamp battery. An AA cell could be used  with a spacer or modified spring.

  

Universal Avominor Model E       

1940-49    Military model of the Universal Avominor

K = 1/2 switch like the full sized Model D; calibrated fuse corner like older Avometers. No AC ranges

DC 2, 20, 200, 1000 volts - sensitivity 1.25 mA
DC 4, 40, 400, 2000 volts - sensitivity 2.5 mA
DC 20, 100, 200 mA, 2, 20
R 10k ohm (500 ohm center)


Universal Avominor  model 2  

1951-56


From 1952 advert

Higher sensitivity meter

DC 5, 25, 100, 250, 1000 volts - sensitivity 250uA
DC 1, 5, 25, 100, 500 mA
AC 5, 25, 100, 250, 1000 volts - sensitivity 250uA
Non-linear scale for 5 volts
R 200k ohm (4000 ohm center)

inside

An extra board holds Welwyn resistors for the higher voltage ranges.

I am indebted to DavePhilpott for these images of his 1955 meter.



AVO Multiminor Model 1 

  Introduced late 1950's

AVO Multiminor Model 2

This is a panclimatic version but otherwise the same

AVO Multiminor Model 3

Probably does not exist


Larger 3 inch moving coil meter

Multiminors Mk I-V all had the same sensitivity and ranges
DC 2.5, 10, 25, 100, 250, 1000 volts - sensitivity 100uA
DC 0.1, 1, 10, 100, 1000 mA
AC 10, 25, 100, 250, 1000 volts - sensitivity 1 mA
(no non-linear scale)
R 20k, 2M ohm (125, 12.5k ohm center)

Wireless World advert 1958:

This sturdy multi-range test meter is remarkable for the wide range of test facilities which have been so neatly incorporated. Full advantage has been taken of printed resistor techniques to produce a compact instrument of low weight.Features:

Composite printed resistors and robust range switch similar to that used in the famous AvoMeter. Eighteen fixed silver plated contacts embedded in a ring of high-grade moulding material are swept by a double contact rotor arm. Meter movement is enclosed to give protection against the infiltration of dust.

7 D.C. Voltage Ranges: 0-1,000 V. 5 A.C. Voltage Ranges: 0-1,000 V.
5 D.C. Current Ranges: O-IA.
2 Resistance Ranges: 0-20,0000ohm 0-2M ohm
Sensitivity:
10,OOO ohms/Volt on D.C. voltage ranges.
1,OOO ohms/Volt on A.C. voltage ranges.
Accuracy:
3% of full scale value on D.C.
4% of full scale value on A.C
For a small additional charge instruments can be supplied to a higher degree of accuracy.

19 Ranges· Single Knob Control· List Price: £9:10s.
Complete with test leads and clips. Leather case if required 32/6.

AVO Multiminor Mk 4  

 1964 to mid 1970s

Ohms scale moved to bottom of scale plate, germanium rectifier if not before.

MULTIMINOR MK4
The current model (1970) of this famous Avo instrument is styled on modern lines, with high standards of accuracy, improved internal assemblies and incorporating panclimatic properties. A single rotary switch selects any one of the 19 ranges. Two scales are provided for current and voltage readings and another for resistance measurements.

The instrument is supplied in an attractive black carrying case, which also houses a pair of leads with interchangeable prods and clips, and an instruction booklet. A robust simulated leather case is available if required.
Size (including case): nx4xHin.(197x102x41 mm.).
Weight (including case): 1 t lb. (0.675 kg.).

SPECIFICATION Current Ranges:
D.C.100µA to 1 A f.s.d. in 5 ranges.
A.C.10V to 1,000V in 5 ranges.
D.C.100mV to 1 ,OOOV f.s.d. in 7 ranges.
Resistance: 0 to 2M ohm in 2 ranges (first indication 5 ..
Sensitivity: D.C. voltage ranges 10,0000/V. A.C. voltage ranges 1 ,0000/V.
Accuracy: A.C. voltage ranges 2.75% of f.s.d.
D.C. voltage and current ranges 2.25% of f.s.d.

MULTIMINOR Mk 4 £12.75 Carrying case £2.80


Note that the shunt for the highest range is no longer printed and that the switch wafer does not have printed adjustment resistors.

Click here for instruction manual

Click here for service instructions

 
mk5

AVO Multiminor Mk 5

mid 1970s



The multiminor instruments were eventually superseded by the Avometer Model 70 series  which were introduced in the early 1970s see here


International symbols, design like Model 8 Mk 5 and new meter movement and minor internal changes.

Click here for instruction manual



Acknowledgments

Images other than those of the meters in my possession have been gleaned, cleaned up and resized from various sites on the internet.


The basic details of the instruments have been compiled and provided by Andrew Usher who felt that there was a need for an AVO page similar to that for Simpson meters shown here: www.simpson260.com


25/03/16