Mullard Circuits for Audio Amplifiers wave listener and building my own one valve receiver (Radio Luxembourg on Metres and Horace Batchelor’s adverts. This is the book that jump-started the boutique tube guitar amp business. Learn the truth about tube preamp design and modification; see how tube power amps . TABLE 1 Classification of Mullard Circuits Power Amplifiers of General Application Power Amplifiers of Special Application Five-valve, twenty-watt circuit (”);.

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This can lead to wow or flutter after much use.

Their loading should be independent of frequency, otherwise the input signal to the amplifier will also vary with frequency. The larger components should be fitted to the chassis in the positions indicated in the layout diagram of Fig.

Two separate pieces of 16 s. The small ampplifiers resistors should be laid across two tags and the lead wires bent around the tags in the manner shown in a above. This equalisation is best incorporated in a pre-amplifier, so that the scope of application of power amplifiers can be increased without any resultant fall in the standard of performance.

Mullard Power Amplifier c | Preservation Sound

The excursion of the working bias is still kept very small under driven conditions. The output of some pick-up heads varies slightly with this vertical movement so that the pinch effect can be an additional source of distortion. Also, the information contained in this mullxrd does not imply any authority or licence for the utilisation of any patented feature.

Amlifiers maximum level with a centre-tapped heater is only 1. If a dual-ganged potentiometer is used, a special balance control is required. Such a dual system may consist of two direct radiators- for example, a 12 in, unit amplfiers the bass-end of the spectrum and a 5 in. The amplifier should thus be capable of handling peak powers considerably above the average level to allow peak sounds to be reproduced without overloading and audible distortion.

Mullard 520 Power Amplifier c.1956

Circuit Design Although the power-handling capacity of an audio amplifier is not the property which is most important to the listener – a low level of distortion is usually considered to be so – it is nevertheless the prime concern of the circuit mulllard.

The negative- feedback voltage from the secondary winding of the output transformer is introduced across the resistor R3 in the cathode circuit. Initially, an increase in the a. Magnetic pick-up heads moving-iron and moving-coil have basically constant-velocity characteristics, the output voltage being proportional to the velocity of vibration of the pick-up stylus.


The smoothing component R22 can only be chosen when the type of tuner to be used is known. A comparison has been made in Chapter 3 between the distortion in the output stage when speech or music signals are used with normal and ammplifiers loading conditions and this comparison is shown in Fig. In spite of the high level of feedback used 30dBthe circuit is completely stable under open-circuit conditions.

Hum and Noise Contributions to the output from various stray signals picked up at points in the amplifier are normally assessed together, and are often measured as the voltage developed at the output when the input is short-circuited to earth.

When a nominal, cathode-biased, class AB stage is examined under the corresponding fixed-bias conditions with a sine-wave input, it is found that, at high output levels, distortion is greater than when cathode bias is used. A stereophonic cutting stylus is triangular and has two cutting edges which are set symmetrically about the vertical at right-angles to each other. Mains input plug, 3-pin.

When the valve is sited in an obviously doubtful or unsuitable position as, for example, in tape recorders, a flexible mounting for the valveholder or a separate weighted sub-chassis is advisable. This is known as ‘constant-velocity’ recording.

It is expressed as a percentage ratio of the power associated with the particular harmonic to the total output power of the amplifier. The main feedback loop includes the whole circuit, the feedback voltage being derived from the secondary winding of the output transformer and being injected in the cathode circuit of the EF The cans should be insulated from the chassis and the negative connection made to the common earth lead.

Mullard Circuits for Audio Amplifiers

A value of about 6kfi would be suitable for typical current and voltage requirements of approximately 35mA and V. INPUT STAGES A low level of hum and noise is essential in the input stage of an amplifier because high gain is required in this stage to provide a good signal-to-noise ratio and to compensate for the reduction in gain resulting from the use of negative feedback.

Voltages between 20 fod lOOmV High-output heads: Thus, the poles of each section of the tape would be adjacent to the like poles of the neighbouring sections. Several types of pick-up stylus are available particularly for use with standard monaural recordsbut the most common for both standard and microgroove discs is the permanent or jewel-tipped stylus.

The function of mullagd chapter is to give brief accounts of the main items of associated equipment needed for disc or tape reproduction and also to discuss some of the causes of distortion, indicating the methods by which imperfections are minimised. The power efficiency that is, the ratio between the audio output power and the d. Most transport systems are standardised for playing speeds of either Yh, 3h, 7 M. With stereophonic tapes, adjacent paths are used for the twin signals comprising the programme.


Standard records are made with diameters of 10 or 12 inches and provide playing times of about 4 or 5 minutes. The feedback resistor R8 should be of the high-stability type. However, as the amplification factor of the ECC83 is highthe effective gain of the cathode-coupled circuit is still about 25 times.

Consequently, the design of amplifying equipment will normally proceed from tjbe to input, the requirements of the output stage dictating to a large extent the design of preceding stages. The stopper resistors R15 and R16 in the control-grid leads and R20 and R21 in the screen-grid circuits have been included as a normal measure to prevent parasitic oscillations.

B9A nylon-loaded valveholder with screening skirt. Because the characteristics of tape-recorder heads are not standardised, it is impossible to design an oscillator coil that will suit all types of head.

Full text of ” Mullard Circuits For Audio Amplifiers”

This is closely allied to the size of the gap in the recording head. Furthermore, the capacitance must be low to prevent an increase in the phase shift when feedback is used. Because of the direct coupling to the preceding stage, the anode voltage of the preceding valve determines the operating conditions of the ECC This is a common cause of distortion. A nylon-loaded phenolic holder, preferably skirted, is generally adequate. On the basis of the molecular theory of magnetism, the ‘molecular’ magnets in the tape are aligned by the magnetising field: A good margin of stability, a low level of hum, and so on, have never been sacrificed in an attempt to achieve attractive, but less fundamental, properties such as miniaturisation.

The others have only recently been released by the laboratory, and have not yet been published.

Extra stages of decoupling will be required to prevent excessive hum voltage being picked up in the sensitive early stages of the tuner. Because of the variety of signal sources in existence, the range of application of these systems has had to be wide.