This instrument is a compact, portable radio test set capable of testing all components in the modern radio receiver, the main feature being Mutual Conductance method of testing valves. This method ensures an accurate test and operates by means of a variation of grid voltage of the valve under test, giving a reliable indication of the condition of the valve. Another advantage of the use of this method is the application of a gas test to the valve. Rectifiers and diodes are tested by means of the emission test, which is the only way to test these types of valves.
INSTRUCTIONS FOR VALVE TESTING
Once this instruction book has been studied, it will not be necessary to carry it with the instrument, as the roller chart gives all the necessary information for carrying out tests on all valves. The instrument gives a direct reading on the meter scale of Ma/V. and the condition of rectifiers and diodes are indicated on the bottom part of the meter scale, reading good, ?, or bad. On the right hand side of the roller chart, the mutual conductance of the valve under test is listed for comparison with the valve being tested. The end of life point is not listed, but varies considerably with different valves, approximately 60% being a safe figure to operate on. This instrument will not damage any valve in any way, no matter how long the valve is left in the socket with the power on, providing all the switches are set according to the chart. Before switching bottom right hand selector switch from shorts to valves, it is advisable to set selector switches Nos. 1 and 2 to their correct respective settings, as indicated by chart.
To test valves for mutual-conductance, proceed as follows:-
(A) Connect instrument to 240-v A.C. or 6-v. D.C. power supply. In the A.C. model the wiring of the power cord is according to standard practice, i.e. Red and Black 240-v A.C. Green-earth.
In the universal A.C.-D.C. model separate leads are supplied for A.C. and vibrator operation.
(B) Set bottom right-hand switch to position marked line ch., and bottom left hand switch is rotated until meter shows full scale deflection. This ensures correct operating for valve testing, and the bottom left-hand switch marked line adj. copes with supply voltages ranging from 195-v A.C. to 255-v A.C. It is advisable to check line voltages at frequent intervals, as in some districts the line voltage varies from time to time, sometimes giving false readings on valve testing.
(C) Select correct filament voltage as shown on second column of roller chart, the first column being the valve to be tested. The middle left-hand switch is used for this purpose, covering from 1.4-v. to 30-v.
<Page 1>
(D) Place valve in correct socket. (The valve may not light up during shorts test until selector switches are in correct position; this does not apply to all valves.)
(E) Rotate bottom right-hand switch to position marked shorts.
(F) The first test now carried out is that of inter-element shorts. Set selector No. 2 to position L and rotate selector No. 1 throughout all positions from A to L, finally setting both switches to the position indicated on the chart before switching to valve test. If the Neon lights on any position, this indicates that an internal short has developed in the valve. This test will also indicate any leakage between elements as high as 100,000 ohms by a definite glow in the Neon. Sometimes a faint glow may be noticed before placing valve in socket; this may be disregarded, as it is caused by capacity in the wiring of the instrument. If the valve proves satisfactory after this test, the mutual conductance or emission test may be applied, whichever may be the case.
DO NOT TEST FURTHER IF ANY ELEMENTS ARE SHORTING, AS SERIOUS OVERLOADING OF THE METER MAY OCCUR, POSSIBLY DAMAGING THE MOVEMENT.
(G) Mutual Conductance test:- If the last test has been carried out correctly the selector switches Nos. 1 and 2 should be in their correct position, as indicated on the roller chart. The middle right hand knob marked range should now be advanced from 0 until setting corresponds with the information supplied on the roller chart.
(H) Rotate bottom right-hand selector switch to position marked valves.
(J) The button marked valve test should now be pressed, and if the valve under test is in good condition the pointer will swing up scale and read the mutual-conductance of the valve direct in Ma/V., which can now be compared with the correct reading for the valve supplied on the extreme right-hand side of the chart. The button may be pressed for any length of time on any valve, without causing any damage to the valve, enabling a correct reading to be taken.
(K) Gas Test:- This applies only to valves tested by the transconductance method. Press button marked gas test. If the valve is free from gas the pointer will not move from its original position; any movement of the pointer indicates a presence of gas in the valve. The presence of gas does not mean that the valve is useless, but the best results must not be expected from it.
(L) Emission Test:- This test applies only to rectifiers and diodes ( this means a diode only, but does not apply to a multi-element valve, such as a Duo-Diode-triode). The valves tested by emission are identified on the chart in the Ma/V. section, where instead of comparative mutual-conductance reading the valve is marked DIODE, RECT. in the case of half wave rectifiers, or 1st Pl. and 2nd Pl. in the case of full wave rectifiers. Assuming that the shorts test (F) and previous information to that test has been carried out, turn the range control to its correct position (middle right-hand knob) as indicated on chart. It is now permissible to turn bottom right-hand selector switch to position marked valves. The condition of the valve will be indicated on the bottom section of the meter marked BAD-?-GOOD while button is pressed. In the case of second plates of rectifiers set selectors N0.1 or N0.2 or both, to new position indicated on chart, every other switch remaining in position at which already set. Always allow an indirectly heated valve to heat up thoroughly before applying mutual-conductance or emission test, otherwise a false reading may be taken. Some valves of different manufacture will show a small variation in reading, which is quite normal.
MULTI-METER RANGES
The following tests can be carried out without connecting the instrument to any outside source of power:-
MILLIAMPERES, D.C.
OHMS, 0-500 and 0-50000.
VOLTS, D.C.
VOLTS, A.C.
VOLTS, OUTPUT.
The different ranges and operation will be described in their order on the bottom right-hand selector switch.
OHMS:- This operates from a self contained 950 type 1.5-v cell fitted on the chassis at the back of the main panel, and may be replaced by removing the four screws holding the front panel and removing the instrument from the case. The cell pulls straight out of the clip. When fitting make sure positive and negative are in the correct position as marked on the battery panel and are making proper contact.
OPERATION:- The bottom right-hand switch is set at position marked Ohms. The test leads should be inserted in respective positive and negative wanda sockets at bottom of panel and then shorted together. Now adjust ohms adj. knob (middle right-hand) until meter reads full scale. With left-hand switch in ohms position, the reading is direct on top of the meter scale, being 15 ohms centre scale. The current drawn from the cell on this range is 100Ma. for full scale deflection. No current flows while the leads are open circuit.
By moving the bottom left-hand switch to ohms X 100 and again adjusting for full scale deflection, the same part of the meter scale is used, but the reading is multiplied by 100, the centre scale now being 1,500 ohms The full scale deflection current flow on this range being 1 milliamp. A higher range is available by plugging power into the power and using megohms scale up to 10 megs., which is described later.
MILLIAMPS:- To read milliamps rotate bottom right-hand switch to position marked Ma's and bottom left-hand switch that selects ranges from 1 to 250 milliamps. It is advisable to take the initial reading on the highest range, and so avoid, overloading the meter movement. Four ranges are available, of which resistance and tolerances are stated in the first page of the manual.
D.C. VOLTS:- Five ranges of direct-current volts are available at a resistance of 1,000 ohms per volt. The bottom right-hand selector switch is set at D.C.V., and the range required is selected by means of the bottom left-hand switch. As in Ma's, to avoid overload to the meter it is wise to start on the highest range and switch to lower ranges when possible.
A.C.VOLTS:- Five ranges of alternating-current volts operate with a copper-oxide rectifier, the same scale being used as for D.C.V. and Ma's. Set bottom right-hand selector switch to A.C.V. and required range may be selected by means of bottom left-hand switch. The resistance of these ranges are 1,000 ohms per volt, the actual meter movement being .9 milliamps. These ranges are calibrated at a frequency of 50 cycles.
O/PT. V. (Output Volts):- With the bottom right-hand switch in this position and any of the five voltage ranges on the bottom left-hand switch, the operator has a useful output meter, with a large condenser in series with the negative test lead (internally wired), thus effectively blocking D.C. volts and enabling the operator to place the negative lead on the chassis of the radio under test and the plate of the output valve, the reading given being the audio frequency output of the valve. It is advisable to always start by switching to the highest range (1,000-v.), thus allowing the condenser to charge initially, without overloading the rectifier or meter. When first connecting it will be noticed that the meter will advance upscale, and as the condenser charges the pointer will gradually drop back; it is now safe to turn to lower range suitable for your requirements.
For all further tests it is necessary to apply 240-v. A.C. or 6-v. D.C., whichever the case may be, and further adjusting line voltage by setting bottom right-hand switch to line ch. and adjusting meter for full-scale deflection by means of bottom left-hand switch marked line adj. When line has been adjusted for full-scale deflection of meter, the following procedure may be carried out for reading direct the capacity of electros:-
ELECTROS:- By setting bottom right-hand selector switch from line ch. to electros and placing test leads directly across the condenser, to be measured regardless of polarity. Condenser may be electrolytic, paper or mica insulation type. If condenser is in a radio receiver it is necessary to disconnect one end first. The section of meter scale is use is underneath mutual-conductance section, and marked MFD., and the reading on this range is direct-scale reading. If a full-scale reading is obtained the condenser under test is shorting, and no reading at all means an open circuit. Some condensers vary as much as 20% from their rated value; but usually an indication of more than 20% from the rated value indicates some fault in the condenser, which is due for replacement. Short test prods together and use range control for final adjustment.
CAPACITY:- By turning bottom right-hand selector switch to position marked CAP, after checking the line voltage, the reading now cover from .01 to .5 mfd. It is necessary to multiply scale reading by .01; this becomes very simple when the instrument has been used a few times. It is always necessary, when testing any condenser which is wired in a radio receiver, to disconnect one end of the condenser, thus cutting out any resistance or capacity which me be in paralleled with the condenser, which would give a false reading.
MEGOHMS:- This range has a dual purpose, and after carrying out line ch. test, as in all previous A.C. tests, this range would be better firstly described as a low-capacity range, giving readings from .001 mfd. to .05 mfds. When using this range, it is necessary to multiply scale reading by .001, the result being in mfds. When using this range for megohms, line check should be first carried out the then set switch at position marked megohms. The reading is made on the scale directly below the capacity section of the scale, and is calibrated direct in megohms reading from 5,000 ohms to 10 megohms. For a more accurate reading the top ohms scale may be used and multiplied by 15,000, making the centre-scale reading 225,000 ohms, or .225 megohms. The megohms scale, though, usually gives a quick and accurate direct reading.
For any further information as regards operation of the instrument or any enquiries communicate with:
RADAMETA TEST EQUIPMENT,
Fowler Road, Guildford.
ciasteczkowypotwornie