'H' attenuation network, 135 ohms impedance, with calibration reports, metal / wood / plastic / paper, made by V M L Pty Ltd, Melbourne, Victoria, Australia, 1961, used by Telecom Laboratory Services, Strathfield, New South Wales, Australia, c. 1961-1990
The operating controls of the attenuation network are fitted into a metal panel screwed into a rectangular wooden box which has a leather handle on the side of the box and a removable wooden cover secured by four metal clips. There are four rotary control switches which are, from right to left, a two position dial indicating '' or '50', a six position dial (scale 0 to 50), an eleven position dial (scale 0 to 10) for units, and an eleven position dial (scale 0 to 1) for tenths. At the right side of the top panel are 3 terminals labelled 'input' with the middle terminal marked 'E'. At the left side are 3 terminals labelled 'output' with the middle terminal marked 'E'. Two terminals are located together at the centre top side of the panel, marked 'C.P.' and 'E.'.
Accompanying written materials:
Photocopy of the layout of the operating controls on the front and rear panel and schematic diagram of the circuitry, one page.
Calibration report dated 11/12/61, one page.
Calibration report dated 15/12/81, three pages.
Repair note dated 10/12/81, one page.
The top panel of the attenuation network is marked:
''H' ATTENUATION NETWORK' 'DECIBELS' 'V.M.L. PTY. LTD.'
'135 (Ohm symbol) IMPEDANCE' 'MELBOURNE AUSTRALIA'
'MAX. INPUT LEVEL 27 D.B.M.' 'TYPE AT. 6-135 SERIAL No. 740-275'
'ACCURACY:- AUDIO ± ·25% ± ·02 DB.'
'1Mc/s. ± 1% ± ·05 DB.'
Printed and typed information on the paper sticker on the top of the cover of the box from the Telecom MQA Northern Region State Calibration Centre includes 'DATE 01.05.91' and 'THIS UNIT IS NOT CALIBRATED. CALIBRATE ON DEMAND' and 'CALIBRATION DUE: MAY 1993'