This is the Service Manual for the AVO Valve Tester Type
Contents
1. burnt out Fuse blown No anode volts at valve pin No anode volts at valve pin but sereen volts present T Relay Operates and Fails to Clear Should the relay operate due to a suspected faulty valve ani fail to clear after switching off and on again with no valve in panel set Roller Selector switch to read 000 000 000 and remove top cap connecting lead Switch instrument off and on again amo Check mains connector Replace LPI Check Mains Vol tage Selector setting and replace Fi and or F2 Check that links 4 amp Ay are tight and making firm contact Check that links Ay and AS are tight and making firm contact If fault clears the most likely cause of the trouble is a short on the valve panel certain pin s being shorted out to earth by stray vire or solder or a breakdown in insulation If the fault still persists however check ht line for breakdown to earth between Roller Selector Switch on Valve Panel and ht transformer on control unit 8 Adjustment of Protective Relay The relay should seldom require attention but if for any reason parts are replaced the adjustment is simple it only being necessary to position two 4BA screws see Pig 3 It should be noted that the bobbins if replaced should be positioned such that the flux which they produce is additive Operational limits are as follows a Anode overload Relay should operate on 100V short circuit b Sereen o2. INDICATION SECTION 4 Pago 11 Ia CALIBRATION CHECK SECTION 5 Page 11 SETTING THE mA V DIAL SECTION 6 Page 12 THE INDICATING METER SECTION 7 Page 12 SECTION 1 TEST EQUIPMENT REQUIRED a Avo Electronic Testmeter or equivalent de mean Valve Voltmeter NOTE The Electronic Testmeter should be standardised at the appropriate voltages before making any adjustment mentioned in the following See WARNING on page 2 a Set mains On Off switch to the Off position b Open IK Fig 3 and set the panel controls as followst CIRCUIT SELECTOR to TEST ELECTRODE SELECTOR to A and NBG GRID VOLTS to 40 c Connect the Testmeter across RV2 Fig 3 Switch on and adjust RV3 Fig 3 until s voltage reading of 20 8V is obtained Remove the Testmoeter a Connect the Testmeter between G and C sockets on the top cap connection panel or if the panel has been disconnected for servicing to the G end C positions on the tag board at the back of the Unit e Check that at the 13 and 4 marks on tho dial readings of 6 75V and 2 1V are obtained If either or both readings are out of tolerance the dial should be adjusted mechanically to split the error If it is necessary to make an adjustment slacken the three counter sunk screws on the top of the dial which will then be free to move within the latitude of kidney shaped slots After adjustment re tighten serewa and check readings The areas marked O 5 15 and 40 should c
3. 3 VOLTAGE CABCKS YITH NO VALVE UNDER TEST SECTION 3 Page 8 a AVO Electronic Testmeter or equivalent dc mean valve voltmeter b Valve CV491 Standardised for Mitual Conductance at 16mA anode current c Model 7 or Model 8 AvoMeters 3 a Power Valve capable of passing 100mA anode current CV428 o Resistor 680A BH SECTION i ND SERVICING NOTES See WARNING on page 2 NOTE All measurements and tolerances stated do not include those of the testing instrument and where necessary these should be ascertained particularly before commencement of the calibration procedure Where possible the recommended instruments should be employed 1 300 o s ac Supply Operation amp its Relation to Servicing Whilst the instrument is suitable for uso on 50 to 500 c s ac supplies service and calibration should normally be carried out wing a 220 230 50 c s supply The following features play a vital part in the correct operation of the instrument on a 500 o s supply a The two eloctrostatic screens S1 and 52 on the ht transformer prevent spurious mA V readings and care mist be taken when replacing a transformer to ensure that these screens are connected as shown in the Circuit Diagram see Pig 4 b The separate cable forms lying side by side across the instrument ensure that the grid circuit and its associated wiring is kept well apart from the ht wiring to prevent the transference of energy from one circuit to the oth
4. This is the Service Manual for the AVO Valve Tester Type 160 It was apparently only available as a type written pamphlet Note that there are 2 copies of the circuit diagram at the back of this manual Whoever had the manual glued copies of the circuit onto the inside cover and back cover However as the circuit was a bit too large to fit the cover he just cut the component values off Obviously a Pommie serviceman who thought it more important to have a neat folder than a circuit you could use So the few component values shown are all I can give you For what it s worth on the cover he d noted CV428 or 5B 254 M CV491 or 12AU7 U52 or 5U4 RV1 2 5KQ_ set ma V RV2 10KQ_ Neg grid volts RV3 500Q pre set RV4 90Q set Ia 0 10ma THE AVO VALVE TESTER Type 160 SERVICE MANUAL AYO zz Avocet House 92 96 Vauxhall Bridge Road London S W 1 Telephones ViCtoria 3404 12 lines Part No 10072 361 February 1963 THE AVO VALVE TESTER TYPE 160 THE AVO VALVE TESTER Type 160 CONTENTS CHAPTER 1 Maintenance Information CHAPTER 2 Calibration CHAPTER 3 Final Test Procedure APPENDIX 1 Schedule of Spare Parts ILLUSTRATIONS Prontispiece Pig 1 Valve Standardising Circuit Pig 2 Underside of Valve Panel Pig 3 Instrument Chassis Fig 4 Circuit Diagram Page 3 Page 10 Page 13 Page 17 MAINTENANCE INFORMATION SONTENTS TEST EWUIPENT AEQUIRED SECTICN 1 Pago 3 PAULT FINDING gt SERVICING NOTES SECTION 2 Page
5. are should be taken to replace all wire in its original position 10 To remove any knob remove 6BA screw and spring washer To remove knob spindle and skirt release locking pin The switch nut is now accessible To adjust skirt slacken lock nut rotate skirt to desired position and re tighten lock nut Reverse procedure to replace TAGE CHECKS WITH NO Y U Connect instrument to known 220 230V 50 c s supply ensuring that the mains On Off switch is in the Off position and adjust coarse and fine settings of the mains voltage selector panel to match the supply voltage as accurately as possible Set the Circuit Selector to Test and the Electrode Selector to a and proceed to check the relevant electrode voltages as follows l Honter Voltages a Connect the AvoMeter switched to its ac voltage ranges between H and H sockets on top cap connector panel b Switch on and rotate the Heater Voltage switch through the full rango of values the external meter being set to the appropriate voltage range as required c The heater voltage reading on the meter should conform to the voltage limits shown in the following table Due allowance must be made for the limita of accuracy of the measuring instrument for each particular readings d Switch off and remove the meter 2 Anode Voltages a Connect the AvoMeter ensuring that the mains On Off switch is in the Off position and set to its ac voltage ran
6. e result will generally be between 4 and 5mA V see Pinal Test Procedure For greater accuracy it is suggested that readings of grid voltage be plotted against walues of anode current between 10 and 20mA amd the slope taken from the curve at 16mA The valve should now be labelled es follows 2009 dc 16mA de Heer ee ee eee eee eee 242442 4422 CY 491 The valve should be re standardised daily when in use 4 onstruction The instrument comprises two units in a hinged transit case the lid of which is not detachable Electrical connection between the two units is effected by means of two 5 way side by side cables 5 Removal of the Instrument From its Case See WARNING on page 2 To facilitate servicing or calibration of the instrument it is necessary to remove both sections from the casing this being accomplished by the removal of four hexagonal headed bolts which form the feet of the control unit from the underside of the case The control panel will then be released The valve panel can be withdrawn from ita section of the case by the removal of eight fixing screws around its periphery 6 Simple Faults a No dial light indication No dial light indication or meter deflection on SET setting of Circuit Selector b No indication of meter current No indication of meter current and protective relay operates when testing tetrodes or pentodes No mains input Dial light bulb
7. e valve and external meter Set the Neg Grid Volts control at 40 Connect a resistance of 680kD 5 between grid and cathode sockets on the top cap connector panel Set the Circuit Selector switch to position Gas The panel meter should indicate full scale deflection 20 Disconnect tho resistance and switch off Using the recommended AvoMeters the valve should be connected as shown in Fig 1 If unable to use the reeommended meters ensure that those used are of sub standard accuracy the current meter having a maximum voltage drop of 100mV and preferably scaled O 25mA and the voltmeters a sensitivity of 1000 Q V If rectified ac ia used for the ht supply it is essential that steps are teken to ensure that the supply circuit is adequately smoothed the Solartron Varipack is a suitable source The bias supply should be obtained from a suitable battery note polarity of connection The heater supply for the valve may be ac or dc but must be within of the rated voltage a Set the grid bias voltmeter to read 9V b Adjust the ht supply to 200V then by means of successive adjustmenta of the bias and ht voltage controls set the anode current at 16mA the anode voltmeter must read 200W Note the new grid bias reading c The standardised slope for the valve can now be obtained fromt The difference between the two anode current readings i e ImA over the difference between the two grid voltage readings Th
8. er at high mains frequencies If at any time it is necessary to displace wiring within the instrument great care must be taken to ensure that it is replaced in its original position e 2 The 0 02pF C1 and 0 02uF C2 capacitors prevent spurious readings on insulation ranges when the instrument is used at high mains frequencies of Inst Before commencing servicing the instrument should be checked as follows a b c a e 2 g h j x m n 3 Ensure that the mains Qn Off switch is in the Off position Connect the instrument to an ac voltege supply of 200 250V 50 o s of known magnitude Set the instrument voltage adjustment to its appropriate position Switch on noting that the panel indicator is illuminated Set the Mains Voltage Selector fine control such that the meter pointer lies as near as possible to the centre of the zone Connect the AvoMeter in series with the 4 link Using the CV491 standardised in accordance with Pars 3 with 200V de anode volts check that i Por 16mA anode current the negative grid volts indication is within 5 of the standardised value ii The slope mA V is within 5 of the standardised value A reading of amp mA on the external instrument will be equivalent to amp dc current of 16mA through the valve this is the value normally indicated by the anode current controls when the meter is at its null position Remov
9. ge between A and C sockets on the top cap selector panel b Switch on and rotate the Ancde Voltago switch through successive positions the meter being set to the appropriate range as required c The meter readings should be 1 1 x the voltage indicated by the Anode Voltage switch 2 6 per cent a sA a b c a e Due allowance must be made for the limits of accuracy of the measuring instrument for each particular reading g with the Anode Voltage switch set to 100 the actual voltage reading should be 110V 2 46 Switch off and remove the meter Screen Voltages Connect the AvoMeter ensuring that the mains On Off switch is in the Off position and set to its ac voltage range betweon S and C on the top cap selector panel Short the anode of V a to cathode pins 2 and 5 See Fig 3 Switch on and rotate the screen voltage switch through successive positions the external meter being set to the appropriate range as required The meter readings obtained should be 1 1 x the voltage indicated by the Screen Voltage awitch 2 6 Due allowance must be made for the limits of accuracy of the measuring instrument for each particular reading Switch off and remove the meter CHAPTER 2 CALIBRATION 0 CONTENTS TEST BWUIPMENT REQUIRED SECTION 1 Page 10 CHECKING THE NEG GRID VOLTS CONTROL SECTION 2 Page 10 CHECKING THE SET mA V CONTROL SECTION 3 Page 11 CHECKING THE SET
10. mA on the external meter the CT160 indicates a nominal figure of 16mA Remove the CV491 and with the bias control set at 40 connect a 680k0 5 resistor between G and C connections on top cap board Check that with the circuit selector switch set to Gas the CT60 meter shows f s d within 20 Insert a U52 in the appropriate socket sot the circuit selector svitch to test and electrode selector switch to DI Insert the test meter on appropriate do current range in series with the losd from the top cap board D1 to the rectifier anode 15 m Check that for all load switch positions i The CT160 meter reading is approximately in centre of good scale ii That the testmeter readings are within 410 of nominal value Repeat test as in j with anode lon connected to D2 on top cap board and electrode selector to D2 16 varm eee HEH i E zi ms z Lapa J A D j 3 f oe Be se 2 lt 3 1 F g
11. on and vith the instrument set to its teat position allow the valve to warm up Set the panel meter pointer to zero by means of the Neg Grid Volts control The external meter should indicate between 47 5mA and 52 5mA 0 5 x indicated value on Anode Current control 5 the panel instrument indicating zero If required repeat this test at any other settings of Anode Current controls Rp ee 2 Switch off and remove the meter SECTION 6 SETTING THE A V DIAL a b e a e g h 5 With the link open and the SET mA V dial at rest set RVI at its maximum anti clockwise position viewed from the front panel and adjust friction tight the locking nuts of the U shaped stirrup Connect the Testmeter set to a suitable range across RS Switch on and advance the SET mi V dial to a reading of 5 Rotate the RVI spindle further by means of the stirrup in a clock wise direction until the Testmeter gives a reading of 105n If this reading is achieved without further clockwise advancement of the stirrup or if its procurcment necessitates an anti clockwise movement of the stirrup then investigate the accuracy of RI R2 R5 and FRV1 The locking nuts on the stirrup should now be tightened and the reading of 105mY on the voltmeter checked Again check that the de millivolts developed across R5 at the 2ma V and 10ma V settings of the dial are 260mV and 52 5mV 3 Check that the dial can no
12. orre within the indicated area to OV 2 6V 7 amp V and 20 8V 5 respectively 10 Switch off ani remove the Testmeter e a a b c a With LK still open connect the Testmoter set to a suitable de range across R5 Switch on and check that when the dial is advanced to its 10 5 and 2mA V positions readings of 52 5aV 105mV and 260nV 3 are obtained If for any reason the relationship between the dial and the potentiometer has been upset tae procedure Setting the mA V Dial given in Section 6 should be adopted Switch off and remove the Testmeter ON 4 NG INDICATION Standardise the Testmeter at 47V dc Close the link LK aml set the panel controls as follows CIRCUIT SELECTOR to SET and ELECTRODE SELECTOR to A Connect the Testmeter across RV2 and switch on A reading of 47V should now be obtained whilst the meter on the instrument panel should indicate within the zone If voltage reading is correct but panel meter indication is outside zone check Resistors R3 and R4 Switch off and remove Testmeter SECTION 5 Ia CALIBRATION CHECK a b c a e Open the link on the valve base panel and insert a Model 7 AvoMeter set to a suitable de range into the circuit Set up the instrument aml place under test any power valve capable of passing 100mA anode current o g CV428 Set the Anode Current controls to 100mA 9OmA and 10mA switch
13. s possible to the centre of the mark Check that selector settings show 5V of the actual mains voltage It is most important to ensure thet the meter reading in the Set position is maintained at the centre of the mark on the scale for all subsequent tests c Set the circuit and electrode selector switches as given in the table overleaf and connect a 1 megohm 1 resistor across the electrodes on top cap board as detailed under the heading Condition Check that a leakage of 1 megohm 10 is indicated on the panel meter in each case1 13 Circuit Selector Electrode Selector e Condition Svitsh Sitch a R Al Resistor connected across Al and any of the following H C A2 or G 5 2 Al Resistor connected across 8 and any of the following H C or G C H R At Resistor connected across C H or H and any of the following Al A2 S or G c a c a Resistor connected across C and either H or H NOTE In positions C H R and C H chock that beater volts appear across H and H a Check operation of the overload cut out with i An anode cathede short at an anode voltage of 100 Connect a short across Al and C top cap board ii A screen cathode short at a screen voltage of 60 Connect a short across S and C on top cap board e Check the following unloaded anode volts with the Testmeter on appropriate ac range connected across Al and C on top cap board Nominal Volts 60 100 150 250 400 Ac
14. tual ao Volts 66 110 165 275 440 Lasits 2 6 Check the following unloaded heater volts with the Testmeter on appropriate ac range connected across H and H on top cap board in mo aa 2 2 2 5 5 3 5 7 10 2 10 8 20 5 22 41 44 120 130 Ps g h 3 k Insert a CV428 in the appropriate socket set the instrument to the correct electrode selector switch to Al and obtain a balance then check that i By varying the grid voltege an anode current of 100mA is obtainable ii The valve does not osciliate NOTE The meter reading should nov vary appreciably when the hand is placed near or on the insulated anode lead iii By varying screen voltage the anode current varies accordingly Insert a CV491 12A4U7 as si i and standardised for mutual conductance at 16eA anode current with 200V lied to the anode connect the H R Testmoter on 10mA ac range across the Ai Link Then check that i Por 16mA anode current on the CT160 the external Testmeter reading is 8mA ii Negative grid volts is 35 of the standard figure iii Mutual conductance is 45 of the standard figure NOTE The mutual conductance figure for the CV491 will normally be in the order of 4mA per volt at an anode current of 16mA The tolerance specified for measure ment of mutual conductance on the instrument applies only to this point on the mutual conductance control Check that with the anode current set up to E
15. verload Relay should operate on GOV short circuit c The relay should not are excessively on a 200 short circuit on anode or screen a The relay should not operate when checking a 120mA rectifier Before making any adjustments check that the lamp LPI is operative When the instrument is used solely on a 110V supply it may be preferable to replace LPI with a 1007 15 pigmy lamp 9 Servicing the Valve Holder Panel The Valve Holder Panel is connected electrically to the control panel by means of two 5 way side side cables One of these cables embodies two thicker sections 16 012 for H and H leads Connections to tag boards on either unit are shown in Fig 2 The wiring of the valve holders on the panel is in the form of nine separate loops all pins comprising a loop and linking in roller 1 of the Roller Selector Switch This form of loop connection is used likewise for pins 2 9 all nine circuits approximating in length and following a similar route around the panel These loops are further loaded with beads of ferroxcube which sufficiently demp the loop to prevent the valve under test breaking into parasitic oscillation A diagrammatic layout is shown in Fig 2 Perroxcube is also used on leads feeding the selector switch as a precaution against lf oscillation Where it is necessary to replace valve holders these with the exception of the B8B are fitted to the panel with nuts and bolts and are thus easily removable C
16. w be rotated to its 1mA V position and that the motion is eventually arrested by the stop screw on the dial and not by the stop at the end of the potentiometer track Switch off and remove the Testmeter SECTION 7 THE INDICATING METER This is a self contained unit which may be withdrawn from the control panel by the removal of two 2BA screws see Pig 3 When used in the instrument as an anode current null indicator the meter has a full scale deflection for approximately 10mA not critical When removed from the instrument the meter has a full scale deflection of 20pA and internal resistance of 3 2500 When shunted by R9 only see Circuit Diagram the meter has a full scale deflection of 39 8nA FINAL TEST PROCEDURE CONTENTS TEST EQUIPMENT REQUIRED SECTION 1 Page 13 PINAL TEST DETAIL SECTION 2 Page 13 NOTE When all repairs have been carried out and the instrument is re assembled carry out the following final test detail a AVO Electronic Testmeter or equivalent mean de Valve Voltmeter b Model 7 or Model 8 AvoMeter c Valves CV428 CV491 and U52 Resistor 1 megohm 1 e Resistor 680kohm W SECTION 2 FINAL TEST DETAIL Seo WARNING on page 2 a Apply a 500V megger test between the mains input and frame gt Apply a known ac 50 c s voltage in the range 200 250V to the instrument and with Circuit Selector at Set set mains voltage selector until needle on panel registers as near a
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