The Shielded-5 Neutrodyne

Radio Record, Volume II, Issue 37, 28 March 1929, Page 31

The Shielded-5 Neutrodyne

A Little Ambiguity ’ RATHER unfortunate error oceurred with the drawing of the shielded-5 neutrodyne published in our issue, Vol. 2, No. 35. The error occurred in the wiring of the audio stages in the lay-out diagram. It was shown that the "B" -++ 90 was connected to the "B" + 135, and these to B of the last audio transformer. The mistake was that the connection between "B" -++ 135 and "B? -+- 90 was incorrect, as a reference to the theoretical diagram would show. "B" -+- 135 is connected ‘directly to speaker positive and to that ‘only. MORE than one cprrespondent has been puzzled over this, and the following is a typical inquiry from "Kelburn," Wellington :- 1. In the theoretical diagram the terminals shown for "B" + 185: and -+- speaker are not made through any eonnection on the set. To what are they connected? ANSWER: They are connected to one another. 2. In the lay-out diagram the lines meeting tend to make it a little ambiguous in one place. For example, see the connection from "B" -++ 90 to "B" of the last audio transformer. The connection for "B" -- 135 seems to join on to this. ~ Mould this be so? ere See above. . "B? + 585 | is shown as being con- { with the speaker terminals, but ‘is there no other connection for "B" -+- 135?

-- ANSWER: No. "B" plus 135 goes to the speaker only. 4, I intend using 6-volt valves. What should the value of the rheostats attached to the filaments of the two radio frequency valves be? . ANSWER: Actually, 6 ohms will be sufficient, as it is sometimes necessary to dim the filament of the radio frequency valves slightly, but it would be wise to use a 20 ohm rheostat so that if, at any time in the future, 5-volt valyes are used, the rheostat would be sufficient to burn. the filament at the correct temperature. 5. If 6-volt valves are used with a 6-volt accumulator, what would be the value of the R2 resistance? ANSWER: A _ resistance is not necessary under these circumstances. 6. Would it be better to install coils wound on ebonite formers or celluloid formers? What make of coils would you recommend? ANSWER: There are several very fine lines of coils on the market at the present time that would be suitable for this set. Some are wound on ebonite and some on celluloid, both of which are equally efficient. For example, Airzone are on celluloid and Radiokes are on ebonite. "[TNCIDENTALLY," the above correspondent writes, "I would like to express my appreciation. of the wounderful value of the "Radio Record," and the useful hints given to the amateur who wants to. know a bit more about radio than just turning a few dials. I keenly look forward to the issue each Tuesday, and I keep a scrapbook which is invaluable to me containing cuttings (indexed) of all the matter in the "Record" worth keeping for reference purposes, and incidentally, the book has reached goodly pro- . portions."