AERIALISMS

Sun (Auckland), Volume III, Issue 687, 12 June 1929, Page 14

AERIALISMS

When J'our aerial is not in use it should be connected to earth via a switch outside the house.

Leads from the plate should not be placed close to or parallel with leads from the gird.

In the case of a tuned-anode circuit the “earthed” end of the condenser is that which is connected to the H.T. positive terminal.

One advantage of non-microphonic valve holders is that there is less chance of damaging the base of a valve when pulling it out of the holder.

Recent experiments with anti-motor-boating devices suggest that a 4-mfd. fixed condenser is greatly preferable to the 2-mfd. usually employed.

An L.F. choke for a filter output unit should have an inductance value of about 20 henries, and a low D C resistance—say of 300 to 350 ohms.

When making adjustments to an H.T. mains unit always take the plug connecting this to the mains right out of its socket, and do not trust to the switch being “off.”

Do not throw away the little stiffening rods supplied with packets of Glazite, etc., as these rods make excellent spacers when winding coils.

If a piece of stiff paper or blotting paper is pushed over terminal shanks or wires when these are soldered, this will protect the surrounding panel, etc., from “sprays” and flux.

A fuse should always be inserted in the leads from the mains when current is being taken from this source for the loud-speaker field, or similar purpose.

In potentiometer-operated circuits carrying high-frequency currents, a .001 condenser (or thereabouts) should always he connected between the slider of the potentiometer and that end which would otherwise be in the H.F. circuit.

If you are taking H.T. from the mains and are troubled with a si hum, it is a good plan to insert the primary or secondary of an old L.F. transformer in series with the H.T. to the detector lead, as this very frequently effects a complete cure.

When a potentiometer is to be used for volume control at the low-frequency end of the set its resistance should be equivalent to that of a grid leak in the same place, i.e., a quarter megohm, half megohm, or so.

When winding solenoid coils over a ribbed former it is a good stunt to cut little grooves for the first and last wires to fit into, and there will then be no tendency for the windings to shift along the former, as they will he anchored securely In place by the end turns.

If you are often fiddling with a terminal in a rather inaccessible place, do not forget that it may be an advantage to cut a slot across the top of it with a hack saw, afterwards using a screwdriver to tighten the terminal. (Many manufacturers have adopted this plan as standard.)

Another serious disadvantage of a low-resistance voltmeter is that when connected across the source of potential it is measuring it passes such a heavy current that the conditions obtaining are radically altered, and therefore a misleading reading is given.

A faulty grid leak is, as a rule, fairly easy to detect, simple methods being satisfactory in nearly every case. A loud howl or ticking noise when the reaction coupling is fairly tight is a sign that the grid leak is either cut right put of circuit or of much too high a value.

Serious distortion also results sometimes from a defective or unsuitable grid leak.

Where transformers are marked OS and IS and OP and IP it is usual to connect the OS to grid and IP to plate. If your L.F. transSormer is not clearly marked to indicate the correct connections, try changing over the leads w-hich go to the primary or to the secondary as they may make a marked difference to strength of reception.

The absence of a large condenser across each H.T. plus tapping and H.T. negative is not very noticeable in some circumstances, for instance, when the H.T. battery is new and giving its full-rated voltage. With an older batter}', however, absence may be shown by cracking or “frying” noises, or if low-frequency amplifiers are used, perhaps a tendency to hoivl when the set is just on the oscillation point.

Mr. G. Wendt, who arranged special broadcasts for KDKA to the Polar regions, says that radio users in the Arctic regions cannot employ accumulators, and therefore operate entirely from dry-cell batteries. But it was found that the “life” of these batteries in store was not long enough to last the season, and after experiment it w-as proved that by freezing them they are made quite inoperative. So when they want to put a new one in circuit they have to thraw it. when all the little watts bob up again as fresh as paint.