DC AvoMinor Introduced 1933
This one in described here was made in 1938
Military Air Ministry Testmeter
Type C With leads and Case stores ref 10S/78 is
essentially the same
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.
later models have one piece magnet and stepped sides to
Bakelite case.
DC AvoMinor introduced 1935
This one described here 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)
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DC AvoMinor (High Resistance) introduced 1938
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.
AVO low resistance ohmmeter
I am indebted to Dave Philpott for these images of his 1941 meter.
Universal Avominor Model 1 (22 range)
Introduced about 1934
Military versions: Air Ministry Testmeter Type H and Navy
AD PATT 13301 see below
right. It is likely that this model was also supplied to the War Office
as I have seen leather cases marked ZD00116
The moulding of the front panel was amended to include has raised surrounds to the sockets. This is typical of meters from the 1940s
Radically different moulding with recessed sockets
This model has a 1500V range but no 250V range
(you may also find meters with a 1000V range)
later design
I have several in my
collection made made between 1935 and 1952, they continued to be
made
into the
mid 1950's.
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.
This Type H
Universal Avominor was made in May 1945 and this maybe one of
the last with the old moulding shown above for the 22 range model 1. It
would have been made under a government contract for the RAF the 10S/46
is a stores reference number. (all radio equipment started with 10)
Note the absence of the trimming resistor on the 5V AC multiplier at
bottom RHS, there is a direct link to the range resistor. Plus the not
so obvious difference on the AC/DC/Ohms switch assemby. (Photo supplied
by Leigh Tuckerman) The leather case for this meter has a RAF stores
reference 10A/10614
A version was also made for the Navy
AD PATT 13301 with
appropriately labelled instruction plate. Some models had this engraved
on the top face of the housing .
Testmeter Type E
1940-49 This is a Military model of the Universal AvoMinor known as Testmeter Type E with leads and Case AM stores ref 10S/10613
The earlier models perhaps until late 1945 were housed in a
purpose designed and identified smooth faced moulding (see first
picture)
K = 1/2 switch like the full sized Model D; calibrated fuse in left hand 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)
Type E connecting leads No.5 10S/10616
Type E with leads and Case 10S/10613
Type E Leather carrying case IOS/10614
Type E Battery 5]/1723
Type 16 Fuse Testmeter, type E 10S/10615
But look at this instruction plate of a 1944 instrument, the
stores references are 10A/ rather than 10S/
Universal Avominor model 1A
1955
Additional low ohms scale 0-200Ω otherwise similar to model 1
An extra board holds Welwyn resistors for the higher voltage ranges.
To use the Low Ohms range, short the COM NEG and 20,000 OHMS sockets, and adjust for zero. The resistance under test is then put across 2.5mA and 500mA ports.
I am indebted to DavePhilpott for these images of his 1955 meter.
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)
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.
This is a model from 1968 which has a board on which are
mounted the swamp and meter shunt circuit comprising two potentiometers
and two resistors. Some later models will only have the lower
resistor
and potentiometer
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
