Neutralising the 2RF B-D.

Radio Record, Volume II, Issue 43, 10 May 1929, Page 29

Neutralising the 2RF B-D.

I SAW your note re neutralising shielded 2RF Browning-Drake.. I have done most of the coil-winding and wiring of three of these sets. In each case I found it absolutely impossible to neutralise on the circuit given in last May’s "Radio Record,’ and so have reverted to another method which is much simpler to operate, and as far as I have found quite OK. I am using a primary aerial coil of 24 turns jumble-wound top-end to earth, bottom to aerial. With this set I have been troubled with too much volume, and when rheostats turned too low then distortion creeps in,

so I have solved the trouble this way and find it very effective and efficient. I have put a .0005 variable condenser in series in the aerial with a switch across it so as to cut it out for weak stations. This I have tried with a dozen other makes of sets, and found effective with all of them, and may be a help to others suffering from the same trouble. As for the 2RF B.D., I cannot say enough in praise for it, and with my experience the biggest job is to get an audio to stand up to the output of it. Only one audio circuit, in my opinion, is satisfactory, and that is the pushpull. I have tried eight different types with five different makes of transformers, and they could not take the output without distortion at less than quarter the volume. This can put out

far too much volume for comfort, so I advise anyone considering building one of these sets to got in for nothing except push-pull audio.-B.D. and PUSH-PULL (Nelson). The method of neutralising is that known as split primary, and should be equally effective as that originally

described. However, the 2RF B.D. works well as described. Failure to neutralise means wrong values or too high voltage on the detector. The parallel feed described in "Guide" gives excellent results, and should make the two R.F. even more popular. There is no doubt if volume is to be handled, push-pull is the best amplifier (described by "Pentode" in our issue of November 2). Primary Variation. W D. CAMPBELL writes: Re neu- * tralising of Browning-Drake, wind | another wire on with primary (about — 15 turns, primary the same), the primary connections are the same, but there is no central tap. The start of primary and the finish of the other . wire (both 30’s), go to B +. The finish of primary, of course, goes to plate, . and the start of the other to neutralising condenser. : This method I have found very satisfactory. Use one wire of cotton-cover-ed and one enamelled. |