INTRODUCTION The TF 2600 is a wide-range a.c. voltmeter of high sensitivity and stability; 12 ranges, giving full-scale deflections from 1 mV to 300 V, enable voltages down to the order of 100 to be measured. An amplifier-rectifier type instrument, it maintains good accuracy with moderately distorted waveforms. A cathode follower input stage, with associated attenuators, regulates the signal level to a four-valve amplifier,, the output of which energizes a moving coil meter via a full-wave crystal rectifier. The meter is calibrated in terms of the r,m* s* value of a sinewave, but responds to the average value; it is also calibrated in decibels relative to 1 mW in 600ft, giving a range of -72 to +52 dBm. The output of the amplifier section is made available at a pair of f ront-panel terminals. This provides a pre-amplifier facility, having a response similar to that of the instrument as a whole, with an output of up to 300 mV on any range.