Double-grid Valves

Radio Record, Volume II, Issue 24, 28 December 1928, Page 25

Double-grid Valves

Queries from Correspondents RIOR to and following our special issue, in which a single stage amplifier using double grid valves was described, we have had questions regarding this type of valve. These are not to be compared with the pentode style of valve, in which there are three grids and which requires a high plate voltage, though it is connected in the set in the same manner, The valve is primarily intended to give maximum amplifiction at low voltage pressure, and is thus admirably suited to single stage amplifiers. which are to_ be worked solely from batteries. However, the following questions and answers show their wider application :-- : 1. "Gan double grid valves be suvcessfully used in an ordinary circuit, such as a neutrodyne, without alterations to the wiring, providing the amplification factor, ete., are suitable?" Yes, circuits using two or more of these valves have already been deseribed, and according to another letter give great resu‘ts.

2. "Can double grid valves be used in a push-pull amplifier, and, if so, how much yolume will such an arrangement carry without distortion?" _ hey are. not suitable valves for last stage owing to their low undistorted output. Their special application has been mentioned above. 3. "Could you please publish the characteristics of the different makes of these valves?" As far as ean be ascertained Philips 441 is the only suitable double-grid obtainable in New Zealand. Following are its characteristics: Filament voltage ..-..--.-. 4.0 Filament current .....--+-- 9.08 Anode voltage ...-- eeseveves 2-20 Auxiliary grid voltage --+++. 2-20 Total emission ....sseeeee+ 20 Amplification fa@tor ...-+-> 4,5 Mutual coductance (Slope) 1.0 500 Internal resistance ....+-.+ 40 Negative grid bias ....+..++-. 4.5 Normal anode current, M.A. 90.9 Anode grid capacity ...--- 2.0 4, "What is the total B current consumed by one of these valves?’-A. C. SIME (Otago). me, See above table-Normal anode. current. ) )

R. SIMSON (Auckland) writes: * "Tf have an N.Z.R. circuit set with two audio stages, using all double grid valves with the following voltages: Set. 44 B. first and 163 B. second and 18 B. The A battery is a 2-volt accum. B battery is a 223 block. The following stations have peen logged: 1YA, 2ZB, 1ZQ, 2BL,° 2FC, 8LO, 4QG, 2YA, 26B, 3YA, 382C,2KY on either speaker or phones. If am always able to get music from one of these stations, and as the set discharges an accumulator in eight weeks and 2 B battery (I don’t know how long, but it has dropped only 3yv. in five months), I think "local station" grumblers should get a similar set and be independent of local. I have also tried a gramophone pick-up, and whilst the volume was there the bass was missing. I am at present building a four-valve double-grid set with many innovations for economy. . Can you tell me any method of getting the bass from a pick-up without increasing the plate voltage? The reproduction of bass notes require more power from the last valve than do the treble notes, consequently to do the bass frequencies justice 4 real power-valve with ample voltage on the plate must be used. ~ Letrodes have not sufficient power output to efficiently handle bass notes in a last stage amplifier. ,