SENCORE SERVICE MANUAL - Pacific TV Online Tube Catalog
Contents
1. MIGHTY MITE TUBE CHECKER ND ANUAL 426 5 WESTGATE DRIVE ADDISON ILLINOIS You have purchased one of the finest instruments that the electronics industry has to offer The TC130 is completely hand wired with no printed circuits It has been tested completely by a competent technician and inspected twice know that there are many reasons why youhave purchased this unit but we would like to cover all of its benefits so that you can fully appreciate them WHAT THE MIGHTY MITE TESTS The Mighty Mite will test all tubes used in portable radios auto radios Hi Fi sets TV sets and also the newest 9 10 and 12 pin tubes recently released It will check over 2500 tubes in addition to picture tubes This is more tubes than any other tester in this price range and as many tubes as laboratory testers test New listings willbe sent to youfor a nominal charge of 2 00 each booklet as new charts are available upon receipt of your signed warranty card WHAT THE MIGHTY MITE TESTS TUBES FOR A new unique principle is used in this tester that will enable you to test for leakage and gas between control gridand other elements shorts between all elements leakage between cathode and heater of 180 000 ohms plus the all important cathode emission test Cathode emis sionhas a special significance here because it serves as a positive quality check if leakage tests have been made first In other words it tests tu2. issiontest the life expectancy can be considered to be much less than if the meter indicated GOOD in a shorter time Also the needle should climb to the GOOD areaand then fall off life expectancy can be considered much less This is also true of picture tubes We cannot recommend that you replace these tubes This decision is up to you or your customer METER PROTECTION Mosttube testers cautions about burning out the meter The meter in the TC130 has built in circuit protection so that you cannot burn out the meter With the FUNCTION SWITCH set to the OFF position the meter is electrically damped This protects it from damage due to jarring REJUVENATION If you wish to rejuvenate a small tube or a picture tube merely increase the filament voltage by setting switch A to one setting higher for ten or fifteen seconds You will also find that this will accelerate gas and leakage con ditions when on the GRID LEAKAGE test If you get a grid leakage reading in the BAD area with a slight increase in filament voltage reduce the filament setting to normal If the leakage reading returns to GOOD the tube is a good tube and should not be rejected If the meter remains in the BAD area replace the tube CIRCUIT DESCRIPTION A complete schematic of the TC130 is shown in Figure 1 The three major tests that determine the quality of a vacuum tube are selected with the FUNCTION control 5 5 These are cathode emission grid leakage and
3. of an inch from the left side of the meter If the meter does not read zero adjust the internal zero ad just potentiometer under the front panel located next to the 12AU7A tube until the meter reads on zero The CAL control and the zero adjust control may interact with each other If so it may be necessary to repeat the adjustments two or three times until both fall into calibration as you switch back and forth HOW TO DETERMINE CONTROL SETTINGS FOR A NEW TUBE Use Tube Manual 1 Determine correct octal socket to use by checking if tube filament pins are 2 and 7 or 7 and 8 If 2 and 7 use socket 1 and if 7 and 8 use socket 2 Ifitisa 9 or 10 pin miniature use socket 3 unless tube has internal connections which must be isolated Switch C will isolate one pin and use of socket 8 will in most cases isolate other unnecessary pins For example a type 1X2 tube is checked in socket 8 because the filament pins 1 4 and 9 Switch Cisolates pin 6 Pins 1 and 9 are isolated in the socket A 12AU7 can be checked in socket 3 since the C switch will isolate the filament center tap Note that there are two 7 pin miniature sockets Socket 4 is used for tubes whose filament pins are 3 and 4 Socket 7 is used for tubes whose filament pins are 1 and 7 such as portable radio tubes 2 Find filament voltage required Set A switchto correctvoltage If filament has a tap isolate it with switch C before inserting tube in socket 3 Findaverage cath
4. D LEAKAGE Note the lower meter scaled GOOD BAD and questionable 7 This important check will locate many tubes that may otherwise be passed If the meter reads in the GOOD area butis slowly moving into the questionable area wait for a minute or so to see if the meter will finally move into the BAD area This is the type of tube that is hard to find on many other testers These particular tubes may not give serious trouble in power output or rectifier stages but should be rejected immediately if operating in high impedance circuits If all tests have been satisfactory the tube is in excellent condition and should not be replaced Please note the cap lead which should be placed on all tubes having caps TO CHECK PICTURE TUBES Use the same procedure as above with the following in mind Use the picture tube socket provided For 110 degree tubes it will be necessary to use an adapter socket which is readily available at your parts distributor Set the filament volt age switch A to 6 for most picture tubes A few new tubes have filaments as low as 2 volts so it 13 a good idea to start at 2 volts and switch up to 6 to be sure that the filament does not burn out Watch the picture tube neck for brilliance The set tings for the other controls are as follows TO TEST PICTURE TUBES Set SWITCH B to G Set SWITCH C to 6 Set SWITCH D to K TUBE LIFE EXPECTANCY TEST If the meter needle climbs very slowly into the GOOD or questionable area on em
5. bes completely In test after test we found that these checks have revealed troublesome tubes tr other testers did not find even expensive dynamic testers WHAT IS THE GRID LEAKAGE SENSITIVITY Thecontrolgrid leakage sen sitivity is over 100 megohms The high sensitivity is realized by using an expen sive moving coil meter Most testers use lower cost moving iron movements This high sensitivity is especially important in circuits controlled by AGC voltage A lower sensitivity of 2 to 5 megohms as found in many tube testers may eventually reject the tube but notduring the time that it is being tested because tube heat causes the leakage to increase with time On some tubes leakage may not reach this low level and the checkers with lower sensitivity will not find the tough dog tube HOW THE MIGHTY MITE III CHECKS EMISSION The Mighty Mite III tests all tubes for cathode emission near their operating current level See page 7 This is very important as many testers do not testat operating levels may test the tube good but it will not work satisfactorily in circuit HOW THE MIGHTY MITE CHECKS FOR SHORTS The Mighty Mite III con tains a new unique circuit to test for shorts between each and every element in tube This circuit checks tubes for interelement shorts at a very low voltage The newer frame grid type tubes requiring a low test voltage can be tested safely and accurately Shorts tests are made by mere
6. designed to select one of the remaining tube pins the control grid or on rectifiers or diodes the plate and short all of the other pins together The sel ected pin and the junction of all of the other pins are used in testing emission grid leakage and shorts as discussed above ZERO ADJUSTMENT THE TC130 MIGHTY MITE TESTER It may be noted that the zero on the TC130 is not at the extreme left as it is onmost meters but rather about a quarter ofan inch up the scale This is because the cir cuit employed is an unbalanced VTVM to accomplish the high sensitivity on grid checks Line voltage changes may cause the zero to fall above or below that marked on the meter The zero potentiometer is the potentiometer located under the front panel It is the potentiometer nearest the 12AU7A tube If you are operating the TC130 in an area where the line voltage is far off 115 volts where the TC130 was factory cal ibrated you may suspect that the TC130 is inaccurate because the meter does not come to rest at zero If so check for zero and make adjustments if necessary as follows a Set the line voltage at exactly 115 volts Set the Function Switch on CAL and adjust the CAL adjustment on the front panel until the meter reads on the CAL on the meter This is located on the far right side of the meter b Switch the function switch to the short test position and note the meter read ing in relation to Zero The zero is located about one quarter
7. e in one of these sockets as indicated in the chart Locate the picture tube socket you will be using this for all picture tube tests Locate the grid cap lead This will be used on all tubes having grid or plate caps OPERATE THE TC130 MIGHTY MITE III AS FOLLOWS 1 Plug line cord into 105 to 125 volts 50 to 60 cycle AC receptacle 2 Locate tube in set up chart in cover Tubes are listed numerically and al phabetically Looking to the right of the tube listing note the set up information r controls A and D and the tube socketnumber Some tubes have more than listing This is for tubes that effectively have more than one tube in an envelope Each section is tested independently 3 Set the controls as indicated and insert the tube in the socket indicated Where more than one listing is shown make complete checks using each listing Short test need be made only once on most tubes 4 Set the FUNCTION switch to CAL and set the meter to the line marked CAL on the extreme right hand side of the meter by adjusting the small shaft marked CAL You need not make this adjustment every time the tester is used however before rejecting a tube that is questionable check to see that the meter is cali brated with the tube in the socket 5 Next switch the FUNCTION switch to the test desired You will find some ways to short cut these tests but for a complete check proceed as follows a Set FUNCTION switch to SHORT TEST and swi
8. e open resistor and re place Locate open connection Description 01 mf 10 200V 20 mf 70V 01 mf 600V 1 mf 2007 NE2 bulb NE2E with holder 0 1 MA moving coil 300 ohm 10W tapped 140 ohms 6K potentiometer 10 meg 1 2W 5 2P9P switch 11P12P switch 2P11P switch Fil trans 1P12P switch 5P5P switch 12AU7A Socket Octal Socket 10 pin Socket 7 pin min Socket Novar Socket Novar Socket 5 pin Nuvistor Socket 9 pin min Socket Loctal Socket compactron BLACK _ _ _____ _______ _ ____ il Ral R3 R4 2200 6807 R2 ol 6 220 G sia H 518 J 4 ue B __ 43 RED 35 RED YELLOW Yy BLU 16 BLUE YELLOW 12 6V ORANGE IOV _BRN YEL a 40 cave onar WHITE L5V YELLOW BLK WH rs MAN FILAMENT BLK vi 108 125 50 60 CYCLE Vi RECTIFIER AMPLIFIER 26 6 ae HH VIOLET 5 FUNCTI OFF EMISSION GRID LEAKAGE SHORT TEST CAL TC DC VOLTAGES TAKEN WITH FUNCTION SWITCH IN CAL POSITION SETUP 470 SETUP 130 SCHEMATIC
9. full scale This is an important feature because 1 it is impossible to burn out the meter even with a shorted tube or with the load set ting on the wrong position and 2 it permits more usable range on the meter scale from 0 to 75 ma GRID LEAKAGE The grid leakage test circuit uses the same basic indicating circuit Actually the grid leakage test circuit could be considered as an ultra sensitive ohmmeter The break between the good and the questionable areas on the grid leakage scale repre sents approximately 200 megohms and the break between the questionable and the bad areas represents approximately 100 megohms In use the control grid of a tube under test is connected through 10 megohms to ground All other elements are connected to approximately 40 volts the arm of the Calibrate adjustment control If a tube has grid leakage or emission a posi tive voltage will be developed across the 10 megohm resistor with respect to ground which is then fed to the 12AU7 grid and causes the meter to indicate The more leakage there is the higher the meter will read towards and then into the bad area until finally a dead short would cause the meter to read full scale Leakage of 100 meg or a grid emission current of approximately 0 5 microamp would pro duce a leakage indication just into the bad area SHORT TEST Shorts between elements of 180 000 ohms or less are indicated by a simple neon indicator A capacitive voltage divider al
10. lows less than 35 volts to reach a tube under test This is important especially in the newer frame grid tubes where breakdown can occur with higher voltages As switch D is rotated each pin or element is checked against all of the other pins for shorts gas or leakage up to 180 000 ohms In the H K position of switch D heater to cathode leakage will be indicated A dull glow indicates some leak age in a tube The 0 1 mf condenser in series with the neon indicating circuit reduces the effect of normal tube conduction lighting the bulb on one anode true short will light both anodes of the bulb Disregard dim flashes in the shorts indicator Note Some tubes have internal connections between pins These tubes will show shorts and are indicated on the tube chart with an asterisk SWITCHING AND SOCKETS Referring to the complete schematic Figure 1 note that all tube pins except fil aments first go through SET UP switch and then SET UP switch Switch is special switch that has beendesigned to let all pin connections feed through in positions and 12 but in any other position one of the pins is opened For ex ample the schematic shows all pins feeding through except the first position which is open In number 2 position this lead would be open etc Switch C is used to reject one of two control grid leads or a filament center tap that otherwise would prevent normal testing procedure Switch is
11. ly rotating Switch D through all posi tions while observing SHORT IND HOW TO CHECK HORIZONTAL OUTPUT TUBE PLATES Theplateof any tube picks up very little current when measuring cathode emission Likewise plates or screens seldom open up However the horizontal output tubes with plate caps can open because of excess heat So it is a good idea to check the plate current sep arately after making the emission test Here is how you do it Leave the tester set up for emission Then set switch B to J and set switch D If theplate is O K the meter will read The amount of current indicated by the reading is not important as this does not change with age It is either good or bad openor connected Tap the plate cap to be sure that the reading stays con stant NEW MECHANICAL FEATURES The Mighty Mite has number of mech anical features not found on other tube testers First note the four additional tube sockets to check the latest tubes Sockets have phosphor bronze contacts for long life The set up chart on the inside cover is another handy feature The all steel carrying case not only insures maximum protection but adds a modern appearance to the instrument TO ACQUAINT YOURSELF WITH THE MIGHTY First note the four controls marked A B C and D These are the four controls that you will be set tingup from the chart Next note the ten sockets numbered one through ten You will be inserting the tub
12. ode current with normal bias from tube manual Set Load Switch according to chart below CATHODE CURRENT SWITCH B SETTING 50 ma 20 50 ma 15 30 ma 10 16 ma 6 12 ma 2 7 7 2 o 8 5 or less QJ HJA P 4 If tube has two Grid pins or Plate pins etc isolate one pin with switch Refer to schematic Figure 1 for connections between switch and sockets If pin isolation is not required set C switch to 6 5 Find control grid pin and set switch D to pick up this pin If tube is a rec tifier set switch D to plate pin Refer to Schematic Figure 1 for connections between tube pin and D switch SERVICE AND WARRANTY All Sencore products are guaranteed to be free of defects due to workmanship when purchased Any defective unit returned to the factory service department at 426 5 Westgate Addison within 90 days after purchase will be serviced free of charge In no case will a unit be replaced with a new unit All Warranty Cards must be in the factory office within 10 days after purchase of the unit Any unit that has been mishandled or misused will receive a charge for both parts and labor regardless of date of purchase No unit will be serviced without charge for either parts or labor after one year of manufacture regardless of circumstances Run numbers are stamped on chassis to denote date of manufacture Please tell us what you think is wrong with the unit when you send it in for repair If you wish
13. shorts betweenelements The FUNCTION control alsois used toturn the unitoff and place a short across the meter position 1 and to check calibration of the unit position 5 Calibration could be compared to Line Adjust in some older testers If some trouble should develop in your tester a few minutes spent in studying the circuit will help you to find the defect and get your tester back into operation BASIC CIRCUIT The basic indicating circuit is essentially a single ended vacuum tube voltmeter using 1 2 of al2AU7 tube asan amplifier Although only one tube is used the cir cuit is ultra sensitive and has many outstanding features One of the main features is the EgIp response With zero volts on the grid input to the 10 meg resistor the meter in the cathode circuit will read very low less than 0 1 ma As voltage is applied and gradually increased the meter current will rise linearly untilit reaches approximately 0 75 ma with 5 volts applied to the grid circuit At this point bias on the 12AU7 is almost zero and any additional voltage applied to grid is dropped across the 10 meg resistor due to grid current flow Consequently approximately 40 volts is required to make the meter read full scale 1 0 ma This broad response feature is used to advantage in both the emission and grid leakage tests as will be described in this section With the FUNCTION switch in the CAL position i e approximately 40 volts at the arm of the CAL po
14. tch D to H K position b SHORT IND lamp will glow if leakage of 180 000 ohms or less exists between heater and cathode in any tube While in the SHORT TEST position rotate switch D through all settings from to A Watch the SHORT IND lamp for additional shorts or leakages be tween elements If the lamp glows be sure that it glows on both electrodes Dimly lit electrodes indicate leakage or gas in a tube Before rejecting tube note whether not this tube is marked withan asterisk in the tube chart If it is this means that there are extra internal connections that will show up as a short and the tube should not be rejected if it lights on these settings only Certain dual section tubes have the cathode of one section tied to the suppressor of the other section These tubes may indicate a short on one position only of the D switch If short is on more than one position of D switch the tube has a short unless otherwise indi cated in set up booklet and should be rejected NOTE A few tubes marked with an asterisk may not show shorts This is because some tube manufacturers use the spare base pins for extra internal connections whereas other manufacturers of the same tube type do not d Set the FUNCTION switch to EMISSION SHORTS TEST was satisfacto ry Set switch D to setting indicated in chart Read the tube emission quality on the top scale on the meter Ifemission checkis OK set FUNCTION switch GRI
15. tentiometer is fed directly into the 12AU7 grid circuit The CAL potentiometer is adjusted for fullscale meter current with the tester set up and the tube to be tested in its socket B CATHODE EMISSION TEST Cathode emission of a vacuum tube is tested by applying an AC voltage to the grid or plate if the tube is a rectifier or diode and measuring the amplitude of the pul sating DC present onthe cathode All tubes are tested at or near normal operating current levels The gridis used asa pick up of cathode current because it was learned that nearly all current flows to the grid in testers where grid and plate are tied together By leaving the plate open an emission test can be made between the grid and cathode and tests turn out the same as if the plate were connected The pulsating DC on the cathode of the tube under test is reduced in the voltage di vider 5 6 meg and 10 meg and applied to the grid of the indicator circuit through 10 meg and 01 mf to ground This network filters the signal so that pure DC is present on the grid of the 12AU7 A tube with normalemission will cause the meter to indicate at approximately 78 ma 100 on the EMISSION QUALITY scale of the meter If emission 15 lower than normal a proportionately lower meter reading will result At 50 of normal the meter will read the BAD area If emission is higher than normal the meter indication will be compressed as described above such that it will never exceed
16. to repair your own TC130 we have included a schematic and a parts list of the most needed parts A voltage check compared to the voltages on the schematic should locate most malfunctions SYMPTOM No meter indication on any position of function switch Meter indicates but will not calibrate Meter can be cali brated but will not indicate emission or leakage on some sockets Short indicator glows without tube in socket in some positions of switch D when Function Switch is in SHORTS position Emission measure ments OK but grid leakage will not in dicate Grid leakage measure ments OK but emission will not indicate Short ind glows on one anode when test ing tube for shorts TC130 TROUBLE CHART PROBABLE CAUSE Defective 12AU7 Defective meter Loose connection at meter terminals Defective potentio meter Defective electrolytic Defective 12AU7 Defective CAL po tentiometer Loose connection at tube socket or at switch or D Wire at tube sockets touching C switch improperly set Function switch Function switch Load switch Transformer Defective 0 1 mf condenser CORRECTIVE MEASURE Check tube and replace if bad Check meter if bad replace Check connections Check potentiometer and re place if defective Check electrolytic and replace if defective Check tube and replace if de fective Check pot and replace if de fective Check
17. tube socket in use and wires which feed thru each ter minal on both wafers of switch C If switch C is OK check wires connecting between switch C and switch D for a poor con nection Check wiring at tube sockets To locate short turn TC130 on and set FUNCTION Switch in SHORTS position Then move wires with a non metallic probe until light goes out This will locate shorted wires Center switch properly in each position Check switch and connections to switch Check switch and connections to switch Check switch Check transformer for opens Check for shorted or leaky ca pacitor SYMPTOM Meter reads high above 0 on emission scale with no tube in socket Bad tubes indicate very good full scale Reference Cl C4 C2 C5 12 M1 Rl R11 R12 R15 Sl 53 54 Tl 52 55 1 PROBABLE CAUSE Defective 12AU7 Zero adj pot mis adjusted or defective Line voltage very low Open resistor on load switch Open con nection at load switch or function switch PARTS LIST Part Number 24G130 24638 24614 24627 2061 early models 20G6 later models 23812 14G129 15S15A 14G85 25542 25541 25543 28S10A 25522 255408 1804 2664 26622 2662 26620 early models 26G56 later models 26G23 26G3 26615 26621 10 TC130 TROUBLE CHART Con t CORRECTIVE MEASURE Check 12AU7 and replace if de fective Check pot re adjust pot Locat
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