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The reasons for a welcome change in set design.

(This is a text advert - Soon the superhet would dominate commercial sets.)

Superheterodynes have the following advantages:

1. Stable HF amplification, and
2. uniform selectivity across the tuning range.

Their failings are:

1. Liability to heterodyne whistle by (a) second channel, and (b) excitation of the tuned input circuits from the oscillator;
2. tracking, although generally satisfactory, is not precise on both wave ranges;
3. distortion, or, alternatively, lack of selectivity in the intermediate amplifier;
4. non-uniform sensitivity across the tuning scale unless an intricate circuit system is used by which both the output and coupling of the oscillator are modified with change of tuning;
5. poor sensitiveness to an exceedingly weak input, unless a pre-first detector HF stage is fitted.

In superheterodynes to-day we find, strangely enough, intermediate amplifiers of both higher and lower frequencies than the incoming signal. If of higher frequency, selectivity and amplification will suffer, and if lower the problem of obtaining high selectivity without distortion arises-, together with liability to second channel heterodyne.

Why not, therefore, keep the signal frequency unchanged? Because at the commencement of the vogue of the single-dial superheterodyne the defects of straight HF amplifiers of high gain were:

1. Instability owing to the excessive value of grid to plate capacity of the older type of screen-grid valve;
2. distortion by increase of modulation of the carrier - the variable-μ valve was only just making its appearance;
3. poor selectivity as a result of cross-modulation;
4. the goodness of the tuned circuits declined as the capacity of the tuning capacitor increased, so that sensitiveness as well as selectivity were by no means uniform across the tuning range.

To-day the position of the straight HF amplifier is quite different. The Ferrocart tuning coils, even in a circuit arranged for high selectivity, produce very considerable stage gain, and this can be used to full advantage owing to the remarkably low grid-to-anode capacity of the type of HF valve now available. The HF pentode, as compared with the screen-grid valve, does not introduce effects of cross-modulation. The variable-μ type handles a considerable signal input without distortion by change of modulation, and with the aid of amplified AVC can be arranged automatically to adjust the signal-handling properties so as to be always in a condition of accepting without distortion a signal input in excess of that by which it is actuated. The characteristic of a tuned circuit having Ferrocart coils is such that sensitivity is almost uniform across the tuning range. High selectivity is obtained without side-band cutting, due mainly to filter design and partly to the important fact that amplified AVC renders the receiver insensitive to a slightly off-tune interfering signal. The Haynes two-HF tuner, Model R, typifies all these features, and is a forerunner of a new vogue in receiver design.

At the 1932 Radio Exhibition the Haynes Single Dial Superheterodyne, then nearly a year old, stood alone. To-day it is typical, but is already superseded by the two HF straight set having Ferrocart filters, low-capacity HF pentodes, amplified AVC, and diode detection, a perfectly stable arrangement which sets an entirely new standard for range, selectivity, and quality, with neither background noise nor self heterodyne whistle.

That The Wireless World readers agree with these views is revealed by the remarkable demand for this new product. Haynes tuners, amplifiers, chassis, and radio-gramophones embody exclusive features, and have achieved an unrivalled reputation for outstanding performance. Demonstrations are given every Friday evening from 7.30 to 9.30 pm at the factory and at other times if advice is received by telephone. A 32-page booklet is available on request which describes the new two HF tuner unit and the exclusive Haynes system of Duophase LF amplification, as well as Haynes loud speakers.

A new factory extension of 3,000 square feet now includes accommodation for the London office, and the address is: Haynes Radio, Queensway, Enfield, Middlesex; telephone: Enfield 2726.