Inhaltsverzeichnis
Metrix U61B resp. U61C
Tube testers Metrix U61B resp. U61C; manufactured by Metrix, F - Annecy.
Technical data
- Principle: Tube tester
- Operation modes: Tube tester with DC voltage test
Power supply
- Mains operation: 110, 130, 220, 250 V; 110 resp. at full load 180 VA
Dimensions
- 610 x 400 x 330 mm, 35 kg
Accessories
- Tube adapters (so-called „Camemberts“)
Operation
The Metrix U61 tube tester allows to perform measurements on tubes under realistic operating conditions. These can be taken from the Metrix tube data table, other tube data books or manufacturer specifications - you are therefore not dependent on having the correct card available for a tube or limited to tube list provided by the manufacturer at the time, the set was developed.
The Metrix U61 tube tester consists of various components.
First, it contains an elaborately stabilised power supply. The AC heater voltage can be adapted to the current mains voltage. In addition, the U61 has separate voltage sources for the negative grid bias voltage, two separate positive grid voltages and the anode voltage. All voltages can be tapped at the front of the device via 4 mm sockets or checked with an external voltmeter.
With five measuring instruments, the tube heater voltage, the grid bias voltage, one of two (screen) grid voltages G2, G3, the anode voltage and the anode current can be measured simultaneously and during operation; in the case of rectifier or diode measurements, a series resistor can be connected in the anode connection.
Most operating elements of the tube tester are located on the top of the set: the set has adapters for the various tube sockets, the so-called „Camemberts“, whose shape reminds of the typical French soft cheese. They are plugged into 9 banana sockets on the top of the set and have two or more standard tube sockets mounted on top of each. The unused „Camemberts“ are plugged into spare sockets at the side of the set - when buying a second hand U61, make sure they are present. Adapters manufactured by Metrix or homemade allow additional tubes to be tested on one of the „Camemberts“ if the corresponding socket is missing. Next to this are connections for all nine tube contacts, usually connected to the switch matrix with short-circuit plugs. If the corresponding short-circuit plug is pulled out, an ammeter can be connected for current measurements. The switch matrix on the right can be used to apply each of the available voltages to each tube contact according to the socket diagram. The tube list supplied with the set provides information on the setting of the selectors. If there is no selector setting for a certain tube on the list, the socket circuit diagram can be used to determine relatively easily which voltage must be applied to which contact.
To test the tubes, the set is put into operation, all voltage switches and regulators are moved to the left (counterclockwise) stop, the operating switch is set to the „ATTENTE“ (WAIT) position and then the „MARCHE - ARRET“ mains switch is switched on, the mains indicator lamp lights up. All selector switches in the switching matrix must be in position 2 (earth).
The heating voltage of the tube to be tested is now set; the „TARAGE FILAMENT“ control is set to the current mains voltage until the heating voltage instrument displays exactly the desired heating voltage. The tube to be tested can now be plugged into the corresponding adapter (the adapter letter is found in the tube table) on the top of the set. One heating voltage connection of the tube is now connected to the heating voltage (selector switch of the corresponding electrode in position 3, the other connection remains in position 2), the filament should light up and the tube should be heated.
For the short-circuit test, all selector switches are now set to the „CC“ (short circuit) position one after the other; if the „ESSAI“ (control) indicator lights up, there is a short circuit between two electrodes.
Heating filament control: The continuity of the filament can be checked with the FILAMENT switch, the indicator must light up.
To test the emission of the tube, the selectors are set to the corresponding positions and the grid bias voltage G1 (GRILLE 1) is set first, the coarse level of the corresponding negative bias voltage is selected with the switch and fine adjustment is made with the rotary control.
Only after switching from „ATTENTE“ to „MESURE“ (from WAIT to MEASUREMENT), the anode and screen grid voltages are switched on and can be set with the corresponding voltage range switches and voltage regulators. Two (screen) grid voltages can be supplied, but the corresponding instrument only displays one of them at a time, G2 for the first grid and G3 for the second grid (caution, tripping hazard!).
When the corresponding grid and anode voltages are present, the anode (plate) current can be read on the corresponding instrument, the range is switched downwards from the maximum measuring range. After a short measurement, switch back to „ATTENTE“ so that the tube is not overloaded by a high anode current.
The anode current flowing through a good tube under correct operating conditions can be found in the tube table or in the manufacturer's technical documentation. The slope of a tube can be checked by observing the change in the anode current when the grid bias voltage G1 is altered by 1 volt; the Metrix U61 can also be used to record tube characteristics in this way.
Checking the cathode insulation: if the cathode switch is moved from 2 (earth) to the CC position under test conditions, the cathode circuit is interrupted and the anode current should immediately drop to 0 if the insulation is correct.
For the vacuum check, the corresponding switch is moved to the „VIDE“ (vacuum) position while the measurement is running and a resistor is inserted in the grid circuit; the anode current should not change. If a grid current flows due to a poor vacuum, the anode current increases and the anode current instrument moves visibly upwards by several marks.
To test diodes and rectifier tubes, a resistor of 5000 Ω (switch position 9) or 100 kΩ (position 0) in the case of less powerful diodes is switched into the anode lead, thus reducing the anode current to a safe level.
The U61 can also be used to test glow stabilisers, thyratron tubes and magic eyes; the procedure is described in the manual.
In contrast to many simple tube testers, which only distinguish between „usable - bad“, the Metrix U61 allows tube tests under real operating conditions with DC currents at the grids and anode, resistors or ammeters can be inserted in all electrode connections, etc. The tube table includes the most common tubes, for more exotic tube types you have to build an appropriate adapter and apply the voltages according to the manufacturer's documentation or information in tube manuals.
As a rule, a tube is still considered usable if 70 % of the typical anode current according to the manual is reached.
All voltages can be tapped on the front panel of the device and checked using a high-precision digital voltmeter, for example.
Technical principle
Tube tester with testing using DC voltages under realistic conditions
Tube assembly
Development
The U61, U61B, U61C and LX109A series of tube testers was developed by the measuring instrument manufacturer Metrix in Annecy (France).
Application
The Metrix U61 tube testers were used in Swiss Army signal workshops, but were not used by the troops; the Uem Ger Mech of the troops did not have tube testers.
