Useful Tips

Radio Record, Volume V, Issue 25, 31 December 1931, Page 26

Useful Tips

HERE pick-up leads must neces sarily be long it is a good plan te incorporate an audio transformer with short wiring from its primary to the grid ¢ircuit so that the long leads te the secondary are decoupled from the vaive. \ HEN dealing with R.F. amplification, "B"’ current is small, so there is no danger in. pulling out the R.F. grid-bias plug and trying different tappings while the set is on. \ HEN using flex leads to carry the heater current in an all-electric receiver, be sure that it is possible to do this without dropping the heater voltage. WHEN adjusting a double crystal type of detector a! "ays draw the adjusting control knob back before attempting to find a fresh surface, as in this way you avoid scraping the two crystal surfaces together.

WHEN a condenser intended to he used for ordinary D.C. supply is being tested, the test voltage, should be at least twice the normal "supply voltage, For condensers to bé used with alternating current mains the test voltage should be at least three times the value of the alternating voltage across the condenser. Witu audio valves, and particularly with power valves, it is important always to switch off the set before adjusting the grid-bias plug in its battery. "THD use of "armoured" twin flex for pick-up leads (in which the covering can be earthed) is frequently effective in removing hum. BZ (500D contact is particularly important in a erystal set where’ resistance losses can be serious in the aerial or earth circuit. HEN considering valves of similar characteristics, remember — that, generally speaking, the one with the highest mutual conductance is the best.