View Single Post
Old 22nd Jul 2021, 2:56 am   #12
Join Date: Jul 2021
Location: Melbourne, Victoria, Australia.
Posts: 7
Default Re: AVO 8 Mk5, should I attempt repair, or send it to a repairer?

Hi guys,
Am new here.
I have an AVO model 8 MK2.
Was new in 1959. A long story;BUT
The MK2 had a 37.5 uA meter movement, and c cursory glance at the manual from posted by technotel suggests that not much has changed in 60 years.
The current shunt system provides the damping for the meter movement and converts the instrument to a 20,000 ohm per volt meter.
If the meter connection is disconnected, the meter movement will swing freely as suggested in post #4. if the movement is then shunted with a 6k8 resistor, the meter swing should reduce to the required/normal amount of swing. If the amount of swing doesnt change between with the resistor connected, then the meter coil is open circuit.
If this all works out OK then you have eliminated all of your worries. Just persevere with fault tracing.
My model 8 MK2 failed with the fine wire connection at the 6K8 shunt resistor. A 1.3 volt battery measured 1.6 volt. resoldering the broken wire fixed the problem.
Good luck and just take things slowly.
To measure 2500 volt, just add 30 megohms in series with the 1Kv terminal.

As a comment, a mate who worked in the telephony equipment division at Philips Hendon works in Adelaide, said the AVO was the only meter he ever trusted.
I got mine when it was fully depreciated at Philips. The instrument tech guys fitted new jewels and calibtrated it and it only comes out of its box on special occasions.
Hope this helps,
prumpfy is offline