Points Regarding Wave-Traps

Radio Record, Volume II, Issue 33, 1 March 1929, Page 27

Points Regarding Wave--Traps

-R.S. (Auckland) writes asking the following questions :- 1. I wish to build a crystal set and wave-trap inside a Lucos coil screen, but find that a 38-inch former at 60 turns that signals are loudest when the coil is halfway in. What can I do to get the same signals full in? I want 1YA only. ANSWER: It appears as though there are too many turns on the coil, although the correspondent has not made his point clear as to what he means by: the coil halfway in. Generally, to reduce wave-length take off turns, and when the condenser reduces it to 0, it would indicate that there are too many turns. A wave-trap should not be shielded. 2. My B battery registers 18 volts, using a Philips 141 valve. Is it necessary to incorporate a choke and condenser?

ANSWER: No. A choke and condenser is necessary only when a large output, greater than that which the valve in question can handle, is to be dealt with. 8. An ingenious diagram embodying wave-trap, crystal set, and direct aerial, is sent, and the correspondent wants to know if it is correct. ANSWER: It is O.K. 4, Is a fixed crystal a Foromodenser all right as both can be fitted into the tin? ANSWER: This we cannot say. The best plan is to try. 5. You say, "To find the number of turns on a coil, divide the wave-length by 7." What size does this imply? ANSWER: If tuned with a .0005 condenser, and the coil wound on 2 3inch former, this would give the requisite number of turns. 6. Is it possible to adjust the condenser so that by means of the D.P.T.D. switch it would be unnecessary to tune on each occasion? ANSWER: It would be possible, but it is rather too complicated to be worth while.