Laboratory Jottings

Radio Record, Volume III, Issue 11, 27 September 1929, Page 25

Laboratory Jottings

Mullard Valves. E have received from Speddings Limited, a full range of the new Mullard valves, and have been able to test each valve in its particular place in the set. Four distinct series are now produced: Two, four, and six-volt and A.C. valves. Hach range is complete, being equipped with general purpose, high frequency, audio, power, detector, sereen grid, and pentode valves. The full range of the new valves is as follows :-

Of these new valves, the following merit special attention :- The special detectors: 2D, 4D, and 6D. This is a very fine series of very sensitive valves. They will oscillate on very low voltage, and give a high amplification without distortion. They are not easy to overload. Sereen grid valves: The Mullard sereen grid valve has a very high amplification factor and steps up the signals yery considerably. The plate is taken from the terminal at the top of the glass. The pentode: The pentode in this make of valve is known as the Pentone, and mpares very favourably with other’ pentode valves. It has been found that if a station is on the borderline of readability anda pentode is introduced in the last stage, it will

be brought in at satisfactory strength. However, ‘a pentode can be easily overloaded, and it is advisable to keep a power valve handy to prevent this happening. For roundness of tone the set owner is advised to introduce the — special power valves, 252, 254, or 256. These are capable of giving just. that completeness to reproduction that makes wireless worth while. HE AG. ‘valves have een brought out in three types, two of which

are indirectly heated and use the 5-10 base. 102T is the heater valve and in character is very similar to the Radiotron 227. A.C.3 is ditectly heated and is similar to Radiotron 226. A.C.4 is, strictly speaking, a D.C. valve of the 171A type. It can be used as a super-power yalve in the last stage for sets using battery power, but in this case a resistance would be needed in the filament circuit. The new Mullard valves are sent out in very attractive cartons. These are artistically designed in two colours, and make a very good display. The valves are robust and breakage through ordinary handling very diffcult. They are obtainable in either English or UX base.

. Va , Position yf. ia. va. g. Slope. Ri. v.g. PMLA Det. 2 1 150 36 7 51,000 13 PMIHF HLF. 2 1 150 18 8 22,500 43 PMILF. Audio 2 1 150 11 9 12,000 ves PM2 Power 2 15 150 75 1.7 4,400 12 PM2D Audio 2 .25 150 13.5 1,25 10,700 * 6 PM12 S8.G. 2 15 150 200 87 230,000 12 PM22 Pentode 2. 3 150 82 1.3 62,500 10.5 PM252 Power 2 3 150 5.4 21 2,600 15 PM8 . yeneral 4 06 150 14 1.05 13,000 6 PM8BA Res. 4 06 150 88 .66 55,000 1% PM4+ Power 4 1 150 8 1.8 4,450 12 PM4D Audio 4, A 150 15 2.0 7,500 43 PM14 8.G. 4 .075 150 200 87 230,000 14 PM24 Pentode 4 15 150 62 2.3 28,600 104 PM254 Power 4 18 150 4.2 2.1 2,000 223 PM5 General 6 .06 150 17.5 1.2 14,700: 43 PM5B Res. 6 .06 150 40 15 55,000 13 PM6 Power 6 AL 150 8 2.25 3,550 9 PM6D Audio 6 1 150 18 2.0 9,000 4h PMi6 == S.G. 6 aA 150 200 --- 200,000 — 6 Pentode 6 17 150 50 2.0 25,000 12 PM256 Power 6 25 150 425 2.0 2,100 223 DFA6 Power 4.5 85 400 .-s« G4 1.45 4,500 30 DFAT Power 4.5 85 400 24 86 2,800 150 DFAS Power 4.5 85 400 19.5 1.3 15,000 Th DFAS Power 6 6 250 5 2.5 2,000 283 D020 Power 756418 2 © 425 5 2.5 2000 a1 PTT eee ee