AVO 8 MK 4

AVO 8 MK 4

The Avometer Model 8 MK 4 is identical to the Model 9 MK 4, which was a more sensitive international version. Looking at the serial number mine appears to have a manufacturing date of 1971. The MK 4 is a design continuation from the previous version and consequently many of its design features are the same as the MK 3. This meter has a 37.5 µA movement, which is more sensitive due to better magnet and coil technology. It also has a printed circuit board attached to the meter movement, which provides permanent shunts, including the protection diode D7 (BY124). The service manual recommends removing D7 if it causes problems when measuring common mode voltage sources. This meter still requires a 15 V battery for the "Ω × 100" range, and a 1.5 V battery for the "Ω" range, however this time they use the metal information plate as the battery compartment cover.

Repairing the shunt resistors is much simpler in this meter compared to the MK 1 and MK 2, because in this one, the coils are smaller requiring less wire, thereby making it cheaper as well.

The MK 4 has a plastic back cover that had a tendency to crack along the lower pair of corners. The plastic was usually grey in colour and became easily scratched. It was a single piece mould with an integrated battery compartment and simple wiring arrangement.


Avometer Model 8

There are also changes to the range selector switches, which now include discs, that would be cheaper to fabricate, but do not feel as good as those on MK 2. There are also changes to the potentiometers, primarily to improve the shaft sealing with the front panel. The movement reverse switch occupies much greater space and appears to be over-engineered, but works well. The faceplate dial is much less cluttered and easier to read, and they finally moved the mirror strip (for parallax correction) to the centre where it would be easier to use.

MK 4 Side View

AC and Ohm Ranges
DC Ranges

In the following sections of this multi-page article you can see the electronic construction, circuit boards, and meter movement components.

This Article Continues...

AVO 8 MK 4
AVO 8 MK 4 eBay
AVO 8 MK 4 Inside View
AVO 8 MK 4 Shunt Coils
AVO 8 MK 4 Battery Compartment and Batteries
AVO 8 MK 4 Back Cover
AVO 8 MK 4 Glass Repair
AVO 8 MK 4 Diode D7 Modification
AVO 8 MK 4 Range Selector Switch
AVO 8 MK 4 Cut-Out
AVO 8 MK 4 Meter Movement Magnet
AVO 8 MK 4 Scale Plate
AVO 8 MK 4 Movement Repair and Balancing