NATIONAL PHYSICAL LABORATORY, 30th August, 1949. C. G. DARWIN, Director.
(The National Physical Laboratory is a Government Laboratory under the Department of Scientific and Industrial Research. It is the highest authority, on standards and measurements in Great Britain.)

REPORT ON TESTS OF TWELVE WATT AMPLIFIER Marked: "POINT ONE" TL/12, H. J. LEAK & CO. LTD.

TEST CONDlTIONS.

In all cases the input was applied to a 50,000 ohm resistor connected to the amplifier by 3 feet of screened cable. The output load was in all cases a resistor of 18 ohms, and the output transformer secondary windings were connected for the " 15 ohms-20 ohms" condition.

TOTAL HARMONIC DISTORTION for 10 WATTS OUTPUT.

0.037 at 1,000 c/s, (0.0003 ratio to fundamental).
0.1% at 60 c/s, (0.001 ratio to fundamental).
2nd and 3rd harmonics predominated, and were approximately equal in magnitude.

HUM AND NOISE.

-80db referred to 10 watts.

SENSITIVITY.

148mV r.m.s. input gave 12 watts output at 1,000 c/s.

LOAD DAMPING FACTOR. (Load impedance/output impedance).

42 for 10 watts output at 1,000 c/s. (Output impedance 0.43 ohms).
45 for 2.5 watts output at 1,000 c/s. (Output impedance 0.40 ohms).
The output impedance was found to be substantially resistive.

FREQUENCY RESPONSE.

Gain relative to that at 1,000 c/s measured at 7.5 watts output, including the losses introduced at the higher frequencies by the capacitance of the input resistance of 50,000 Ohms.