1. Megger Avo Training Institute
2. Avo Megger 210600

This page attempts to provide details of the full size multimeter'sbased upon the design firstmanufactured in 1923. A fairly comprehensive list of all the modelsproduced can be seen in the Notessection at the bottom of this page.Please note that AVO produced quitea number of models and there were also minor variations within oneparticular model or Mark. Please be aware that the inclusion of imageson this page does not imply that I have such a model unless expresslystated, see notes at bottom of this page. The list here is notexhaustive and is' Awork in progress'By opening individual images onthis page in a new window they can usually be viewed at a larger size. DC Avometer'13-range' (Model 2)Introduced 1927.

This one may have been made in 1934A fuse wired in series with meter.DC 0.12, 1.2, 12, 120, 1200 volts -sensitivity 6 mADC 12, 120 mA, 1.2, 12 AR 1k, 10k ohm (12.5, 125 ohmcenter)100k,1M ohm (1.25, 12.5k ohm center) with external power(In fact = 7.5, 75 volt ranges,with no adjustment)The front panel now manufactured from a one piece Bakelitemoulding and the casing made of aluminium.The later model 6 introduced around 1934/5 has a divide by 2button effectively doubling the number of ranges. And terminals for thetest leads.Interior, note that the horse shoe magnet isaligned with the front panel. In the model 6 and later models usinghorse shoe magnets the magnet isat right angles to the panel (see images below)The meter used an inbuilt 1.5 volt rectangular cell for thetwo lower resistance ranges (Siemens type T orequivalent). This was accommodated in a wooden recess on the undersideof the instrument.Later model 6 with divide by two button (click on image). UniversalAvometer'20-range' (Model 3)introduced 1932. This onewas made in November 1932Added AC capability using transformer andcopper oxide meter rectifier rectifier.DC 0.12, 1.2, 12, 120,1200 volts - sensitivity 6 mADC 12, 120 mA, 1.2, 12 AAC 1.2, 12, 120, 1200 voltssensitivity: 6 mA on 120, 1200 volts, 120 mA on 1.2, 12voltsAC 120 mA, 1.2, 12 AR 1k, 10k ohm(12.5, 125 ohm center)100k, 1 M ohm (1.25, 12.5k ohmcenter) with external power(In fact = 7.5, 75 voltranges, with no adjustment).

Universal Avometer'34-range' (Model 4)Introduced 1933A 1934 trade manual advertised this model at12 guineas (£12.60)The 13 range DC only model was also available at the timeAdded 'divide by 2' button - sensitivitydoubled when pressed. Deleted 1.2 V AC range(probably was inaccurate)DC 0.12, 1.2, 12, 120, 1200volts - sensitivity 6/3 mADC 12, 120 mA, 1.2, 12 AAC 12, 120, 1200 voltssensitivity: 6/3 mA on 120, 1200 volts, 120/60 mA on 12 voltsAC 120 mA, 1.2, 12 AR 1k, 10 k ohm (12.5, 125 ohm center)100k, 1M ohm (1.25, 12.5kohmcenter) with externalpower(In fact = 7.5, 75 volt ranges,with no adjustment)(images from Dave Philpott)The meter used an inbuilt 1.5 volt rectangular cell for thetwo lower resistance ranges (Siemens type T orequivalent).

This was accommodated in a wooden recess on the undersideof the instrument. An external voltage was needed for the higherranges.Universal Avometer'36-range' (Model 5)introduced 1934.Added 480 V AC range (240 V when buttonpressed)DC 0.12, 1.2, 12, 120, 1200 volts- sensitivity 6/3 mADC 12, 120 mA, 1.2, 12 AAC 12, 120, 480, 1200 voltssensitivity: 6/3 mA on 120+ volts, 120/60 mA on 12 voltsAC 120 mA, 1.2, 12 AR 1k, 10k ohm(12.5, 125 ohm center) with 1.5 volt cell100k, 1M ohm (1.25, 12.5k ohm center) with externalpower(In fact = 7.5, 75 volt ranges, with no adjustment). Universal Avometer'46-range' Model 7 (early)Introduced 1936. The first one shown here was made in 1944 andthe second in 1945.Note the differences in the front panel mouldings. The second includes'MODEL 7UNIVERSAL' in a sans serif font rather than the more usual'UNIVERSAL'Note also that the zero adjuster on the earlier model is madeof brass and the later ones are black Bakelite.

This seems to be truefor all instruments made after 1944 or thereabouts.Versions of thismeter were made for the British Army and labelled withthe part number ZD00021.those for the Air Ministry were known as Testmeter Type F with leadslabelled with the stores reference 10S/1or 5QP/1. Universal Avometer'46-range' Model 7 (later)Introduced 1936,this one was made in 1948 but this model was still beingproduced at the end of 1951The Model 7 was the first with with auto cut out instead of a fuse anddecimal scale (rather than duodecimal as in previous models) and hasthebasic design on which the model 40 and model8 were based.

It has higher sensitivity and was the first with dB scaleand block magnet assembly for the meter movement. Earlier models wouldhave horseshoe magnet on the meter (see the model 40 below)Bakelite or aluminium case with battery cover designed to holdthe test prods. 19441944Early models have horse shoe magnets and bimetallictemperature compensation 19481948After 1948 (or late 1947)Alnico blockmagnets used for the meter rather than the horse shoe of the earlierinstruments. It seems that meterers with Alnico magnets have an A inthe serial number.AVO used a standard movementdesign for most products, but with small variations. This were referredto as the Movement 45 (1949/1950), which was superseded by Movement 46(1965).Internal 9V battery 2x4.5V Siemens type P3 (cycle lamp type)for highresistance range and as previously a 1.5 volt cell Siemens type T orequivalent for lower ranges.

Other equivalents are Exide B23 and EverReady R1662 which have these dimensions:1.125 x 3.3125 x 1.125 inch /29 x 84 x29mmTherectangular battery became obsolete many years ago and mostowners resorted to soldering a U2 or equivalent cell in its place. Universal Avometer Model 7 Mark IIIntroduced about 1952 and last manufactured1986.This one from wasmade in 1955New movement design but no external changes initially. At somepoint during the 1950's, added power factorjacks for P.F.unit and red and black banana terminals in 1956.

Last manufactured1986.Model 7 Universal AvoMeter MKII (from 1960 advert)A multi-range A.C./D.C. Measuring Instrument providing 50ranges of readings on a 5-in. Hand-calibrated scale fitted withanti parallax mirror.Range selection is effected by means of two rotary, switches,which are electrically interlocked. Full scale deflection on voltageranges is obtained with a consumption of I mA or 2 mA according towhether the -:- 2 press button is used or not. The total resistance ofthe meter is 500,000 ohms.The instrument is self-contained, compact and portable, simpleto operate and almost impossible to damage electrically.

It isprotected by an automatic cut-out against damage through severeoverload.CURRENT: A.C. 0 to 10 amps.VOLTAGE: A.C.

0 to 1,000 volts.RESISTANCE: Up to 40 megohms.AUDIO-FREQUENCY POWER: 0-2 watts.CAPACITY: 0.01 to 20 mFds.DECIBELS: -25dB to + 16dB.POWER FACTOR AND POWER can be measured in A.C. Circuitsby means of an external accessory (the Universal AvoMeter Power Factorand Wattage Unit). Two models of this Unit are available, one for usewith the Model 7 Avo Meter and the other with the Model 40 AvoMeter,but in either case the Avo Meter must be a model fitted with socketsmarked 'P.F.'

For connection to the Unit. All recently produced AvoMeters have been fitted with these sockets. Universal Avometer Braille Model 7 Mark IIIntroduced in 1951, the Braille model 7 meter was modified foruse by visually-impaired servicemen and consisted of a more-or-lessstandard meter with a'feeler mechanism' pointer over the scale, swung from the movement.

Youwill note that the Braille range markers are on the front face ofthe meter rather than on the knobs. There are Braille markings mouldedabove the arc of the scale window for each of the ranges. The switchpositions have similarly-marked Braille mouldings and amilled groove on each of the range selector switches so that thepositionscan be found by touch.This idea was also implemented on the Model 8 which wasintroduced in 1951 though the model 7 and 40 meters continued to haveengraved knobs until the end of production.The markings on the braille scale are said to allow users to interpretreadings to within 1% of FSD.See picture below of a Braille model 8 Mk3This Radio Ham QSL card suggeststhat AVO may have rovided operators with these cards as a way ofadvertising their products. (images from Aitor de Elejabeitia). Universal Avometer Model 40Introduced 1939. This one was made in1946Universal Avometer model 40 re-done after Model 7: same asModel 7except ranges and sensitivity. Until about 1948 meterswouldhave had ahorseshoe magnet such as this one.

Several components including therectifier have been replaced in this instrument. Universal Avometer Model D(AM part number 10S/-47 This onewas made in 1945Military version (Air Ministry). Modified Model 40; Switchinstead of 'divide by 2' button. No Q potentiometer and only tworesistance ranges.DC 0.3, 3, 30,300, 1500 volts - sensitivity 5/2.5 mADC30, 300 mA, 3, 30AC15, 150, 600, 1500 voltssensitivity: 5/2.5 mA on 150+ volts, 50/25 mA on 15 voltsAC15, 150 mA, 1.5, 15 AR1k, 10 k ohm (25, 250 ohm center)This meter only requires a single 1.5 Volt cell unlike themodel 7 detailed above.Therectangular battery became obsolete many years ago and mostowners resorted to soldering a U2 or equivalent cell in its place.

Universal Avometer Model 40 Mark IIIntroduced 1952 This one ) was made in 1975In 1980 this instrument would have cost £124.60 exc VATNew movement design but no external changes initially. At somepoint during the early 1950's power factor jacks forP.F. Unit were added and the banana terminals in 1956. This instrumenthas a germaniumrectifier, which must have been a later change. Last manufactured 1986.Housed in aluminium case.Model 40 UNIVERSAL AVOMETER Mk.II (from 1960 advert)A self-contained multi-range A.C./D.C.

Megger Avo Training Institute

Instrument providing 40ranges of current, voltage and resistance. Higher ranges are obtainablewith the aid of external shunts, transformers or multipliers.Range selection is accomplished by means of A.C. Switchknobs, and in addition a -:- 2 press button halves the value of anycurrent or voltage range. Full scale deflection on voltage ranges isobtained with a consumption of 3mA. According to whether thepress button is used or not.

Total resistance of the meter is 200,000ohms.The instrument is similar in design and appearance to the Model 7AvoMeter, and is fitted with an automatic overload cut-out.CURRENT: A.C. 0 to 12 amps.VOLTAGE: A.C. 0 to 1,200 volts.RESISTANCE: Up to I megohm.POWER FACTOR AND POWER can be measured in A.C. Circuits bymeans of an external accessory (the Universal AvoMeter Power Factor andWattage Unit). Two models of this Unit are available, one for use withthe Model 7 Avo Meter and the other with the Model 40 AvoMeter, but ineither case the Avo Meter must be a model fitted with sockets marked'P.F.' For connection to the Unit.

All recently produced Avo Metershave been fitted with these sockets. High-Sensitivity HR Avometermodel 1Introduced 1948? This one isinHigh-Sensitivity HR Avometermodel 2Note the diffferent ohms scale and buutton labels.First with 20,000 ohmsper volt; no transformer or AC current ranges on this model.High-voltage terminals added.No Q knob or 'divide by 2' button. Permanently attached shunt chaintaking 1/4 of meter currentDC 2.5, 10,25, 100, 250, 1000, 2500 volts - sensitivity 50 uADC0.05, 0.25, 1, 2.5, 10, 25, 100, 250, 1000 mAAC10, 25, 100, 250, 1000, 2500 volts - sensitivity 1 mA(Non-linear scale for 10 V)Rresistance 'Low ohms' (about 3.7 ohms center, reversedsome models lacked this)50k, 5M ohm (500, 50k ohm center)This instrument was available in two versions model 1 andmodel 2, the latter had an extended resistance range andcould measure up to 20 M ohm. Instruments in screened cases were alsoavailable.

Universal Avometer Model 8 (sometimes called'Mark I')Introduced 1951. I don't know when this one was made as the movement is a replacement and undated.Versions of this meter were made for the British Army and labelled withthe part number ZD00579Development of High-Resistance model, added back transformerandnormal switch design.Meter reverse button added. Interior re-design to incorporatecommercially available variable resistors on resistance ranges.Bakelite case with battery cover designed to hold the test prods. Themodel 8 was designed to accommodate the more readily availablecylindrical U2 cell (size D) and because of the higher resistanceranges a small15 Volt battery. Early models of the AVO 8 use the B121. This batterywas superseded by the B154 type (squarer cross section) and in 1970/71AVO started issuinginstruments with an adapter to accommodate the smaller dimensions.The B121 and B154 were made with ten biscuit type layer cells.

Modernequivalents are constructed from round button cells (hence the R in thetype number). The meter battery contactsseem to have been changed in the late 1960's from the flat type shownhere to pointed spring contacts more suitable for the BLR types.BLR121 Height: 36mm. Length: 26 mm.BLR154 Height: 34mm. Diam: 15mm.The BLR121 and BLR154 are both rated at 40mAh.These can still be obtained but prove to be veryexpensive. I have successfully refilled the plastic casing with ten newcells obtained from a 'Pound Shop'.

Universal Avometer Model 8 (military version)AM stores number 10S/16411(AM pattern AP12945)This oneis the same as the model 8 Mk1 except that it is fitted with anextended metal push button with rubber boot to reverse the moving coil.This type of pushbutton was used onsome miitary versions but not alland some if not all have a steel outer casing with an earthing terminal.These instruments preceded the TestSet No.1 (see below) which has ranges in multiples of 1 and 3 like themodel 9 rather than 1 and 2.5 of the model 8. Universal Avometer Model 8 Mark IIIntroduced 1956. This one was made in 1960Added red and black banana terminals.Added 500 volt DC range early in production.The rectifier has been replaced in this instrument.With the change to the familiar red and black terminals newleads andprods were made and the battery cover was a simple piece of metal withtwo keyholes and a piece of expanded rubber to keep the 1.5 Volt cellin place.The following are both PDF files and will open in a separate window(the Mk1and Mk2 had the same instructions)Model 8 UNIVERSAL AVOMETER Mk. II (from 1960 advert)This instrument has been produced in response to a demand for a highsensitivity version of the world-famous Model 7 AvoMeter.

It followsthe standard design, retaining the traditional simplicity of operationand compact portability. It has a sensitivity of 20,000 ohms per volton all D.C. Ranges and 1,000 ohms per volt on A.C.

Ranges from 100 Vupwards.In addition to the many well-known features such as the automaticoverload protection device, dual-knob range selection, etc., it has apush-button for reversing the polarity of the movement to obviate theinconvenience of changing over the leads when encountering oppositepotentials in respect to a common reference point.CURRENT: A.C. 0 to 10 amps.VOLTAGE: A.C. 0 to 2,500 volts. Universal Avometer Model 9 Mark IIIntroduced in about 1964The model 9 was intended for the export market and is similarto the Model 8 MarkII apart from the international symbols and 3-10ranges instead of 2.5-10 and the positioning of the anti parallaxmirror.No dB scale; resistance on bottom of scale plate instead oftop; no LR or Ins. PositionDC3, 10, 30, 100, 300, 600, 1000, 3000 volts - sensitivity 50 uADC0.05, 0.3, 1, 10, 100 mA, 1, 10AC3, 10, 30, 100, 300, 1000, 3000 volts - sensitivity:1 mA on 100+ volts, 3 mA on 30, 10 mA on 10, 30 mAon 3AC10, 100 mA, 1, 10 AR2k, 200k, 20 Mohm (20, 2k, 200k ohm center)The rear of the front panel of a Model 8 MkII (the switchingarrangement for models 7,8 and 40 etc is much the same). Test set No.1(NATO part number 6625-99-105-7050) military version of Model 8/9MarkIIThis one in wasmade in 1971Note thatTest set No1 was made for several years and was based upon the currentcommercial model at the time.(see model 8 Mk5 below)Test set No.1 (a military version of Model 8/9 Mark 2)Essentially the same as Model 8 Mark 2 apart from 3-10 ranges insteadof 2.5-10; no dB scale; resistance on bottom of scale plate instead oftop; no LR or Ins.

At some point added fuse on low ohmsranges.This model is housed in a protective steel case.No dB scale;resistance on bottom of scale plate instead of top, noLR or Ins. PositionsDC3, 10, 30, 100, 300, 600, 1000, 3000 volts - sensitivity 50 uADC0.05, 0.3, 1, 10, 100 mA, 1, 10 AAC3, 10, 30, 100, 300, 1000, 3000 volts -sensitivity: 1 mA on 100+ volts, 3 mA on 30,10 mA on 10, 30 mAon 3AC10, 100 mA, 1, 10 AR2k, 200k, 20 M ohm (20, 2k, 200k ohm center)Later versions of 'Test Set No. 1' wereessentially identical to the Mk 5 (to 1986)and Mk 6 (from 1986 toend of Avo use). Universal Avometer Model 8 Mark IIIIntroduced about 1964. This one inwas made in 1968Replaced copper-oxide with germanium rectifiers to improve ACsensitivity and frequency response (typically 20K Hz at 2.5V). Thesewere not incorporated in Model 9 untilthe Mark 4 version.Fuse added to low ohms ranges. Early models of the Mk3 do notincorporate the additional protection features described below andshown on the circuit diagram.DC 2.5, 10,25, 100, 250, 500, 1000, 2500 volts - sensitivity 50 uADC0.05, 0.25, 1, 10, 100 mA, 1, 10 AAC2.5, 10, 25, 100, 250, 1000, 2500 volts -sensitivity: 1 mA on 10+ volts, 10 mA on 2.5AC100 mA, 1, 2.5, 10 AR2k, 200k, 20 M ohm (20, 2k, 200k ohm center)Also LR (= 0.325 volts, for use with low range of Resistance RangeExtension unit) and Ins.

(2 M ohmcenter, with external power)A miltary versionof the 8Mk 3 (AM stores number 10S/16411) with extended Rev MC buttonwas also made like that shown on the earlier model above.Looking at the diagram on the rightthe meter has thermal compensation plus additional protectiondiodes around the movement and in circuit with the ohms range. The ohmsrange was vulnerable to putting it across AC so the diodes back to backwould protect the meter and draw the current through the fuse.

Also adiode across the movement deals with AC on a DC setting so protects themovement, so it sees 1/2 the waveform thus tripping the mechanicalmovement otherwise the movement would just see AC and not movetherefore not cut out and ultimately be destroyed. Previous models itseems would not be protected if on the DC setting but were connected toa high AC supply voltage.

Universal Avometer Model 8 Mark IVIntroduced 1969. This one inwas made in 1971In 1980 this instrument would have cost £98.50 exc VATNew internal construction using PC boards. Wired connectionsto battery compartments.Reliability problems with this model (nomilitary versions). 2.5 A range replaced with 10 mA and resistancemoved to bottom of scale plate to match Model 9. AC sensitivityincreased againDC 2.5, 10,25, 100, 250, 500, 1000, 2500 volts - sensitivity 50 uADC0.05, 0.25, 1, 10, 100 mA, 1, 10 AAC2.5, 10, 25, 100, 250, 1000, 2500 voltssensitivity: 0.5 mA on 25+ volts, 1 on 10, 10 on 2.5AC10, 100 mA, 1, 10 AR2k, 200k, 20 M ohm (20, 2k, 200k ohm center)Also LR (= 0.325 volts, for use with low range of Resistance RangeExtension unit) and Ins. (2 M ohmcenter with external powerHoused in plastic case. Mirror placed mid scale rather than atbottomas on all previous versions.

This was the last model to have leatherrather than plasticcarrying strap.Avometer Model 8 Mk 4(from 1970 catalogueThis multi-range instrument has been designed to meet the requirementsof radio, television and electronic engineers requiring an accurate,sensitive yet robust instrument. The Avometer Model 8 Mk 4 incorporatesall the traditional design features of its predecessors, so highlyvalued for Simplicity, together with such additional features as:increased sensitivity in the lower a.c.

Avo Megger 210600

Voltage ranges, fused ohmscircuit to provide increased protection against inadvertent overload inthe lower resistance ranges, improved temperature coefficient enablingmeasurements up to 500 amps d.c. To be made with the aid of a range ofshunts, and improved frequency response. It also incorporates thefamiliar Avo automatic cut-out mechanism and a decibel scale for audiofrequency tests.SPECIFICATIONAC 10mA to 10A f.s.d. In 4 ranges.DC 50uA to 10A f.s.d. In 7 ranges.AC 2.5V to 2,500V f.s.d. In 7 ranges.DC 2.5V to 2,500V f.s.d. In 8 ranges.Resistance: 0 to 20M ohm(First indication 0.5ohm).Decibels: -15dB to + 15dB.Accuracy: AC Voltage and Current ±2.25% of f.s.d.DC Voltage ±2% of indication.

Current ±1% off.s.d.Sensitivity: AC voltage ranges 2,000 ohms/V(10V upwards).DC voltage ranges 20,000ohms/V (all ranges).Size: 204 x 185 x 115 mm.Weight: 2.95 kg. (including leads).(click on image)This is the first model to havewired connection between the battery compartment and the meter. Thespare fuse is housed in a hole on the right. Access byremoving the back cover.This meter was equipped withan electronicvoltage converter which was supplied from the 1.5Voltcell.

This item is normally supplied with a flexible printed connectorthough in my case the previous owner had soldered wires to the 1.5 Voltcell to power the unit. See for moreinformation.Introduced 1969. This one in has no date. Avometer Model 9 Mk 4(from 1970 catalogue)The Avometer Model 9 Mk. 4 is a high sensitivity instrument for themeasurement of voltage, current and resistance. It is designedprimarily for the electronics engineer and is similar in specificationto the Avometer Model 8 Mk. The Model 9 incorporates all thetraditional design features of the Model 8 including the Avo automaticcut-out mechanism and reverse moving coil facility.The Model 9 is, however, scaled in basic units of 10 and 3 and allrange switches, controls and terminals are identified by graphicalsymbols, which in general follow the requirements of the InternationalElectrotechnical Commission.The protective devices incorporated in the Model 8 Mk.

4 are allretained and an insulation resistance range now enables measurementsup to 600A to be made using a range of external shunts. The decibelscale is, however, not included on this instrument.SPECIFICATIONSimilar to the Test set No 1 (see above)A.C. 10mA to 10A f.s.d.

In 4 ranges.D.C, 50uA to 10A f.s.d. In 7 ranges.A.C. 3V to 3000V f.s.d.

In 7 ranges.D.C. 3V to 3000V f.s.d.

In 8 ranges.Resistance: 0 to 20M a (first indication 0.5 ohmAccuracy: A.C. Voltage and Current ±2.25% of f.s.d.D.C. Voltage ±2% of indication. Current ±1% of f.s.d.Sensitivity: A.C. Voltage Ranges 2000 ohms/volt (10V upwards).D.C. Voltage Ranges 20,000 ohms/volt (all ranges).Size: 204 x 185 x 115mm.Weight: 2.85kg.Price each £34.80. Avometer Model8 Mark VIntroduced 1972.

This one inwas made in 1973TestSet No1 Mk3 (66) is the military version of thisinstrumentNewinternal and external design including movement, the new plasticfront-panel no longer includes the word 'Universal' Plastic casingredesigned. Leather carrying handleabandoned for a plastic one. Instrument much lighter than all previousmodels.dB scale and LR range deleted. (But LR could still bemeasured withResistance Range unit.) Adopted Model 9 ranges and added 600 volts ACrange.DC 3, 10, 30,100, 300, 600, 1000, 3000 volts - sensitivity 50 uADC0.05, 0.3, 1, 10, 100 mA, 1, 10 AAC3, 10, 30, 100, 300, 600, 1000, 3000 volts -sensitivity: 0.5 mA on 30+ volts, 1 on 10, 10 on 3AC10, 100 mA, 1, 10 AR2k, 200k, 20 M ohm (20, 2k, 200k ohm center)Also Ins.

(2 M ohm center, with external power)AVO METER MULTI RANGE MMR14C/2The Model 14C Avometer is a Model 8 Mk5 made to aBritish Post Office specification. It is essentially the same apartfrom front panel markings and a different instruction plate on the back. Avometer Model 8 Mark 6Introduced early1980's This one in wasmade in 1984New internal design using rigid PC boards (less rugged)instead of flexible wiring. Deleted high-voltage terminals.DC 3, 10, 30,100, 300, 600, 1000 volts - sensitivity 50 uADC0.05, 0.3, 1, 10, 100 mA, 1, 10 AAC3, 10, 30, 100, 300, 600, 1000 volts -sensitivity: 0.5 mA on 30+ volts, 1 on 10, 10 on 3AC10, 100 mA, 1, 10 AR2k, 200k, 20 M ohm (20, 2k, 200k ohm center)Also Ins. (2 M ohm center, with external power)The military version 'Test SetNo. 1' was essentially identical to the Mk 6.

Avometer Model 8 Mark 7Introduced 1992Only change from the Mark 6 was the addition of a 10 A fuse inseries with all ranges.Last manufactured 2008.Precision AvometerIntroduced 1963/4 This one inwas made in 1967RANGESDC1.5V to 1500V and 1.5mA to 15AAC 3V to 1500V and 3mA to 15ASensitivity 100 Ohms/Volt on DC and AC except for 3V AC range which is50mA fullscaleDesigned to provide anaccurate and stable local reference or transfer standard for industrialand laboratory engineers. It meets the requirements of Section 6 of BSS89/1954 for precision grade instruments ie:D.C. Voltage ranges 0.3% of f.s.d.D.C. Current ranges 0.5% of f.s.dThe accuracy on a.c. Voltage and current ranges is 0.75% of FSD (formfactor of 1.11) This accuracy is maintained for audio frequency testsup to 1 kHz on ranges up to 3OOV.Temperature correction:true value= 1+.0003(t-20) where t is ambient temperature in degreesCelsiusRange selection is accomplished by means of two controlsmechanically interlocked with thethirdcentral control to select voltage or current as required. Two 7 inchscales calibrated 0to 150 and 0 to 30 cover both voltage and current measurements.

A testcertificate is provided for each instrument housed in the lid. (notshown)Precision Avometer Mk2made in June 1970Pictures of Mk2 supplied by Adrian AlmondThe Welwyn blue high stability precisiion resistors wereintroduced by AVO in about 1968 to replace the wire wound types used onprevious models throughout their range.NotesJust to give you all an idea of variants of the Avometer.There are some interesting variants here that may have only ever hadsmall production runs. Thanks to Andy Gilham (Megger/AVO) for this listof official variants.