Leak tl 50 plus owners manual

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Page 1

OPERATION

'TLIEO PLUS'
POWER AMPLIFIER

é ﬁbmm E
t.-

.LEAK

swam INSTALLATION - OPERATION - MAINTENANCE

NOTES ON THE CHOICE AND PERFORMANCE OF LOUDSPEAKEH SYSTEMS

For Service Manuals Contact
MAURITRON TECHNICAL SERV'CES
8 Cherry Tree Rd, Chinnor
Oxon 0X9 4QY .
Ts|:~ otmaslssd Faxt- (844352554
Emailz- enquiries@mauri1ron.oo.uk

l. The TL/SO PLUS may be fed from the LEAK VARlSLOPE MONO preaamplilier, or from any other
suitable source. This LEAK preampliﬁer is supplied with a black multiple connecting cable terminating in
an OCtal plug which ﬁts the socket on the TL/SO PLUS' marked PRE-AMP'. and automatically makes the
input connection. In this casethe input GAlN control should be turned fully clockwise, An input ofl25mV
r.m.s. will give a power output of 50 watts.

2. When a LEAK pre-ampliﬁer is not used the input connections should be taken via a screened co-axial cable
to the plug ﬁtting the socket marked lNPUT', and the GAIN control adjusted to suit the signal level,

INSTALLATION

3. Check that all valves (tubes) are correctly seated in their holders and that the markings on the valves corres-
pond with those on the chassis adjacent to the holders. The ampliﬁer will work equally well with any of the
alternative valves.

4. The ampliﬁer should stand on its base in a well-ventilated position. If placed in a case or cabinet, ventilation
must be provided. Four separate ﬁxing feet with screws are provided with the ampliﬁer, and these nmsl be
ﬁtted, so raising the bottom of the ampliﬁer, and allowing circulation of air.

5. On the British model the mains transformer is tapped for voltages of 200, 213, 226 and 239 and the voltage
selector plug on top of the mains transformer (see ~TOP CHASSIS drawing) should be set appropriately.
On the US. model the mains transformer is tapped for voltages of IOO, 108. lift and |24 and the voltage
selector plug should be set appropriately. The A.C. power supply is connected to the two terminals nearest
the guide key on the removable plug portion ofthe mains connector marked A.C. POWER', and the supply
frequency can be either 50 c/s or 60 c,s.

In order that the ampliﬁer may be remotely controlled we have provided two terminals marked SWlTCH'
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 link. the flex being
passed through the adjacent grommet marked SWlTCH CABLE. The ﬂex should be knotted behind the
grommet to avoid strain on the SWITCH terminals. Most users will wish to make use of the switch incor-
porated in the volume control of an associated LEAK prevamplitier', which is supplied with a plug and twin
ﬂex for this purpose. Full details are given in the installation sheets which accompany every pre-ampllﬁer.

6. A double socket 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 l00 watts or
thereabouts. This socket is not fused but is controlled by the ampliﬁer switch.

7. 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 corres-
ponding terminal on the ﬁxed portion ofthe connector is marked on the chassis by the symbol rah is very
bad practice 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 groundedt No other earth connections
should be made elsewhere, particularly when a pre-ampliﬁer is also used, if freedom from earth loops and
hum is to be obtained.

Page 2

8. The loudspeaker should be connected by a flt'isltd pair of wires to the plug marked LOUDSPEAKER. It
will be seen from the circuit drawing that one side ofthe loudspeaker winding is connected to the chassts, and
no part ofthe loudspeaker wiring should be earthed elsewhere. The DC. resistance of the connectingWires
should be as low as possible, and not more than one-tenth the DC. resistance of the loudspeaker. lt 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 Changeover switch which replaces it With
a resistor of corresponding value and rating. The selector plug on top of the output transformer (see TOP
CHASSlS drawing) should be adjusted for the nearest match to the advertised impedance of the loud-
speaker.

GENERAL NOTES ON MAINTENANCE

The circuit diagram provides a qualiﬁed engineer with all information required for servicing, However, the
following paints may be oi" interest :7

(a) The TL/SO PLUS' does not depend upon 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.

(b) Should it ever be necessary to replace the reservoir capacitor C14 note that it must be ofa type capable of

handling at least ZOOmA ripple current. The CM ﬁtted has a high margin ofsafety, being capable ofhandling
240mA.

NOTES ON LDUDSPEAKER SYSTEMS
Space does not allow for detailed explanation on this vast subject, but the following points should be noted :-

(a) This ampliﬁer will operate any high ﬁdelity loudspeaker system, both moving-coil and electrostatic types,
including the small low sensitivity assemblies currently popular, particularly in the U.S.A.

(b) You cannot get high ﬁdelity results il you mount a loudspeaker in the same cabinet as the turntable and
pickup.

(c) The assembly commonly called a loudspeaker consists 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
consists 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, Bertinek in Acoustics. McGraw-Hill Publishing Co Ltd. First Edition.

((1) One good motor. properly housed. is capable of giving fairly good results. but two good motors, properly
housed. will give noticeably better results: in this case one motor is designed to reproduce bass, and the
other treble. A ﬁlter (dividing network) must be used in conjunction with the two motors.

(0) Remember that even the best conventional loudspeaker systems are by far the weakest link (i.e..the greatest
source ofdistortion) in a high ﬁdelity chain. and that such systems are relatively expensive. The fundamental
weaknesses of conventional loudspeakers are discussed succinctly in a paper by H. J. Leak. High Fidelity
Loudspeakers: The Performance ofMoving-Cnil (Ill E/ec/ros/atic Transducers. Journal of the British institute
of Radio Engineers. Vol. l6. No. l2. December l956. Copies are available front the institution. 9 Bedford
Square, London. W.C.l. price 7 -. However. such systems have become out-moded by the revolutionary
Leak invention ofthe composite sandwich diaphragm. The basic principles are described by D. A. Barlow.
M.Sc. (Head of the Leak Transducer Research Department) in Wireless World. December 1958. A further
paper describing the complete Leak Sandwich loudspeaker system was delivered to the British Institution
of Radio Engineers by D. A. Barlow and H. J. Leak on the 24th January, 1962. and will be published in a
forthcoming journal of the Institution.