The AVO 8 Mk 5 (AVOMETER MODEL 8 Mark 5) was a military approved universal meter (also known as Test Set No 1. Mk 2) first introduced in 1972 and manufactured by the Kent based company AVO Limited. It complied with the British Defence Standard (DEF 155), whilst an identical meter Model MMR 14C complied with the British Post Office specifications.
Compared to the previous models, this one has a tough durable plastic case making it much lighter to carry on the field. The internal electronics including the movement are of simpler design. The most obvious difference is that the shunts are etched onto a printed circuit board (PCB) eliminating the coils as the previous models had. It also utilises flex circuits and cables, which connect the PCBs together. The range selector switch is also different and cheaper where they etched the contacts on the PCB thereby lowering component costs drastically.
There was one minor revision of the mark 5 design, where for models manufactured after November 1981, the 22-kΩ potentiometer (6121-048) replaces the 15-kΩ potentiometer (6120-303). There was also a major revision where RV1, RV2, and RV3 changed from 18 kΩ to 22 kΩ, including changes made to capacitors C4 and C2.
One of the reasons why these meters continue to exist is because of the overload protection mechanism, which cuts the current during an overload condition. This makes the meter extremely useful for beginners who may make mistakes. If you are starting electronics, then a meter such as this is far better because it disciplines you into thinking the correct way such as understanding what you are measuring in a circuit and what to expect. This is far better than automatic ranging meters, which provide a convenience but are not very useful for gaining the correct discipline.
In this multi-page article, you can see the circuit boards, battery compartment, meter movement, and basic design architecture of this meter. You should also look at my other Avometer articles in the series for comparison.
This Article Continues...AVO 8 Mk 5
AVO 8 Mk 5 Battery
AVO 8 Mk 5 Circuit Boards
AVO 8 Mk 5 eBay
AVO 8 Mk 5 Repair
AVO 8 Mk 5 Meter Movement
AVO 8 Mk 5 Dial
AVO 8 Mk 5 Cut-Out Mechanism
AVO 8 Mk 5 Range Selector Switch
AVO 8 Mk 5 Leather Storage Case
AVO 8 Mk 5 User Manual