Experiments with the S.G.

Radio Record, Volume V, Issue 14, 16 October 1931, Page 9

Experiments with the S.G.

I HAV®E been experimenting with the s.g. valve on both ‘short-wave and broadcast for the past twelve months, and I find that enormous amplification can be obtained if they are in matched circuits. I have had four stages of shielded grid working O.K. I first used tuned anode, then parallel feed tuned grid. My first set was an s.g., coupled by tuned anode to an ordinary neutralised triode transformer coupled to det. It worked splendidly. I do not use regeneration on broadcast, as I consider it unnecessary with s.g. circuits, My present set is not exactly the same as the "Outspan," although the circuit is fundamentally. Modifications are: 10-ohm resistances in the ment negative, rheo. in positive, co. and condensers shielded in earthed’ boxes. The coils I evolved from the article in the "Radio Record" on radio-frequency design. They are: Tapped aerial coil coupled to S625, first transformer 75 turns 24 d.s.c., 2in. former coupled to PM16, separately shielded, coupled to second transformer, detector, leaky grid, transformer to PM6. output. The first coil has a primary of 25 turns of 32 s.w.g. wound doubled spaced over wooden matches placed over secondary. This provides the tight coupling necessary. The det. coil is 8in. with 35-turn primary wound the same as before, I have tried several different primaries, but these are easily the best, One modification which I think would improve the "Outspan" is variable voltage control to the screening grids. It is worth all the regeneration put together; put a higher voltage tap on the screen grids, and adjust to below oscillation point; it also acts as volume control. I get plenty of power out of my present combination, and I can get more by careful by-passing and chokes in high voltage leads. Turn out more sets like the ‘Outspan"; they are near the ideal for New Zealand conditions, but bar regeneration, which does spoil the quality. One thing I do not like about the "Record" is that sometimes Questions and Answers and the constructional page are omitted. Now that DxX-ers have a magazine of their own you could eut that page out, as any radio enthusiast can tell you DX-ing is simply a matter of locality. A super-DX set wail not perform in a poor locality. I-have been DX-ing in many different localities, and there is a vast difference in radio reception; therefore your DX Competition is not a square deal. I propose using a pentode with inductor dynamic. Could you supply me with value of audio choke or output device to match valve.-sS.'L.G. (Otago). {You will find all the information relative to matching a pentode to a dynamic speaker in the articles by Mr. Dawson published some time back. -Tec. Ed.] } a