AVO Voltage Converter VC1 I have been given [April 2013] an AVO model 8 Mk4 with one of these and a very leaky 1.5 volt cell. It was connected directly to the cell with wires rather than the flexible printed circuit conductors which are intended to slip between the cell and the meter contact springs. It would always be in circuit and drawing some current.
With a new 1.5 volt cell my unit drew 330 microamps on no load, the unit is rated at 90 microamps max at 15 volts according to its label. An alkaline D cell has a typical capacity of 12000-18000 mAh so should last a very long time if constantly discharged at this rate.
I have opened it up for you see that it has 3 transistors one inductor and sundry components.
The out put as it appears on my oscilloscope [5mV/div and 10uS/div]
An AVO model 8 presents a load of approximately 200 000 ohms to the 15 volt battery when the leads are connected together. I checked the operation with and without such a load and found that it produced a satisfactory output over the range of 0.9 to 1.6 volts.
Note that although the VC1 will fit the Mk4 and later models it will be too big for the Mk1 and Mk2. By removing the screws at either end it will just fit a Mk3. The BLR121 is 35mm overall, the VC1 40.6mm over the screws and 37.3mm between the contact pads