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Re: Leak TL/12 Plus

Geschreven door John Hupse op 16. Feb 2007 22:01:56:

In reactie op: Re: Leak TL/12 Plus geschreven door Maarten van den Brom op 16. Feb 2007 18:02:18:

Maarten,

Op een Leak TL/12 Plus eindversterker zit normaal een 2-polige luidsprekeraansluiting. Deze bestaat uit een isolatieplaatje waarop 2 schroefjes. Wanneer je iets anders aantreft is dit er later opgezet.

De luidspreker wordt aangesloten op de versterker via een getwist snoertje met 2 aders. Het is de bedoeling om circa 1 cm isolatie van elke ader te strippen, en de blanke koperdraad stevig onder de schroefjes van de luidsprekeraansluiting vast te klemmen. De gedachte aan zoiets als een Din plugje zou nooit bij de Leak ontwerpers zijn opgekomen.

Voor de niet-gloeiende buizen zijn er een aantal foutmogelijkheden: er zitten verkeerde buizen in, de 6,3 Volt gloeispanning ontbreekt of er zitten buizen in waarvan de gloeidraad is onderbroken. Het eerste kan je op het oog controleren, met een universeelmeter kan je de andere twee mogelijkheden checken. Maak meteen de buispennen even schoon.

Gebruikershandleiding:

H.J LEAK & Co. LTD.
April 1957
TL/12 PLUS POWER AMPLIFIER
Installation, Operation and Maintenance
Notes on the choice and performance of Loudspeaker systems
The TL/12 Plus may be fed from LEAK "VarislopeIII" and "Point One Plus" pre-amplifiers,or from any other suitable source. A source impedance higher than 25kOhms will tend to raise the hum level above the advertisedfigure of 85 db below 12 watts. An input of 125mV r.m.s. will give a power output of 12 watts.

Check that all valves(tubes) are correctly seated in their holders and that the markings on the valves correspond with those on the chassis adjacent to the holders. The amplifier will work equally well with any of the alternative valves.
The amplifier should stand on its base in a well-ventilated position. If placed in a case or cabinet, ventilation must be provided. Four separat fixing feet with screws are provided with the amplifier.
On the british model the mains transformer is tapped for voltages of 205, 225 and 245 and the fused voltage selector on the top of the mains transformer (see "Top Chassis" drawing) should be set appropriatly. On the U.S. model the mains transformer is tapped for voltages of 105, 110 and 117 and the fused voltage selector plug should be set appropriatly. The A.C. power supply should be connected to the two terminals nearest to the guide key on the removable plug portion of the mains connector marked "A.C. Power" In order that the amplifier may be remotely controlled we have provided two terminals marked "switch" underneath the mains transformer (see "Under chassis" drawing). The amplifier will not work unless these terminals are electrically joined, and when the amplifier leaves our factory a wire link joins the terminals. A remote switch may be run from the "Switch" terminals, after removing the line, the flex being passed through the adjacent grommet marked "Switch Cable" The flex should be knotted behind the grommet to avoid strain on the "Switch" terminals. Most users will wish to make use of a switch incorporated in the volume control of an associated Leak pre-amplifier, which is supplied with a plug and twin flex for this purpose. Full details are given in the installation sheets which accompany every pre-amplifier.
A double socked marked "A.C. Outlets" is fitted as a convenient source of power supply for gramophone motors, self-powered radio tuners, etc. The power taken from this socket should be limited to 100 watts or thereabouts. This socket is not controlled by the amplifier switch or fuse.
Many British tuner units have no build-in power supplies and require a source for heater and anode currents. The octal socket marked "Spare Supplies" on the back of the amplifier is provided for this purpose. The pins are numbered as indicated on the circuit diagram, and connections should be made to the pins similarly numbered on the removable plug which is supplied. The high tension voltage is 350V and on the tuner units it may be necessary to provide a dropping resistor of suitable value, and some units may also require a condenser for smoothing and/or decoupling after the dropping resistor. An earth connection should not be made directly to the tuner units, as this is automatically effected by the above connections via the power amplifier. The maximum current available from the 6.3V terminals is 2.1A and the maximum high tension current is 40mA.
A connection to earth (ground) should be taken from the third terminal on the removable plug portion of the "A.C. Power" connector. This terminal is the one furthest away from the guide key and its corresponding terminal on the fixed portion of the connector is marked on the chassis by the symbol . It is very bad practise to omit this connection, which may be made to the water system or to the steel conduit encasing the house wiring, providing that these systems themselves are properly grounded. No other earth connection should be made elsewhere, particularly when a pre-amplifier is also used, if freedom from " earth loops" and hum is to be obtained.
The loudspeaker should be connected by a twisted pair of wires to the terminals marked"Loudspeaker." It will be seen from the circuit drawing that one side of the loudspeaker winding is connected to the chassis, and no part of the loudspeaker wiring should be earthed elswhere. The D.C. resistancs of the connecting wires should be as low as possible, and not more than one-tenth the D.C. resistance of the loudspeaker. It is bad practice to operate any power amplifier without a loudspeaker, and if it is desired to mute the loudspeaker by switching it out of circuit this should be accomplished by use of a change-over switch which replaces it with a resistor of the corresponding value and rating. The selector plug on top of the output transformer (see "Top Chassis" drawing) should be adjusted for the nearest match to the advertised impedance of the loudspeaker.
GENERAL NOTES ON MAINTENANCE
The circuit diagram provides a qualified engineer with all information required for servicing. However, the following points may be of interest:-

The TL/12 Plus does depend on the output valves (tubes) being a matched pair to give the stated performance, and if one output valve fails it is not necessary to replace both.
Should it ever be necessary to replace the reservoir capacitor C14 (which is in the same can as C13) note that C14 must be of a type capable of handling a heavy ripple current. The C14 fitted has a very high margin of saftey, being capable of handling 380mA. The values of 60mfd and 100 mfd are made high for the sole of minimising the hum resulting from unavoidable "earth loop" which must be occasioned by the connection of non-powered tuner units.
NOTES ON LOUDSPEAKER SYSTEMS
Space does not allow for detailed explanations on this vast subjekt, but the following points should be noted:-

You cannot get high-fidelity results if you mount a loudspeaker in the same cabinet as the turntable and pickup.
The assembly commonly called a "loudspeaker" consits of a magnet, a moving-coil, and a diaphragm (or "cone"). This assembly is a "motor" You do not listen to a motor; you listen to a loudspeaker system, which consits of one or more motors mounted in a housing, (baffle, box, cabinet or horn). The housing plays a profound part in determining the quality of reproduction. The effects of various housings are discussed by L.L. Beranek in "Acoustics" McGraw-Hill Publishing Co., Ltd., 1st Edition.
One good motor properly housed is capable of giving good results. Two good motors properly housed will give noticably better results: in this case one motor is designed to reproduce bass, and the other, tremble. A filter ("dividing network") must be used in conjunction with the two motors.


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Specification

Valves(Tubes)
First stage 1 EF86 or Z729 or 6267
Second stage 1 ECC81 or B309 or 12AT7
Output stage 2 EL84 or N709 or 6BQ5
Rectifier 1 GZ34 or 5V4 or 5AR4

Power Output
14 watts r.m.s. maximum
Total Harmonic Distortion
0.1% at 12 watts output ( ±1db) at 1kHz
Hum and Noise
85dB, ±3db, below 12 watts with a source impedance of 25k ohms
Sensitivity
An input of 125mV at 1 kHz gives 12 watts output
Frequency Response
±0.5db 20Hz to 20kHz
Damping Factor
25, measured at 1kHz
Input Impedance
1 megohm, plus approximately 5 pF
Stability Margins
Gain, 10db ±3db Phase, 20° ±10°
Loudspeaker Impedances
Loudspeakers of any impedance between 3 ohms and 20 ohms may be used. An adjustable plug on top of the output transformer selects three tappings, nominally 16ohms, 8 ohms and 4 ohms.
Power Supply
200 - 250VAc 50Hz - 100Hz
or (alternative model)
100 - 125VAc 50Hz - 100Hz
A fused voltage selector plug is fitted on top of the mains transformer
Consumption
75 watts (80 watts with Leak pre-amplifier).
Spare Supplies
The following supplies are available for a radio tuner unit from a socket at the rear:
Heater: 6.3 V 2.1 A A.C. max
H.T. 350V 40mA D.C. max highly smoothed (0.2V r.m.s. ripple).
A double socket marked "A.C. Outlets" is fitted as a convenient source of power supply for gramophone motors, etc. Corresponding plugs, with 6-ft, (2 metre) cables are supplied with the amplifier.
Dimensions
25,4 * 20 * 15,2 cms
Weight
14.5 lbs or 6,58 kg
Fixing
Four brackets and screws are supplied for fixing the amplifier to a baseboard.
Price :
18£






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