Moving MultiMeters

AVO model 8

AVO used to be a respected British manufacturer of electronic instruments. They are now part of the Megger-AVO company. Their range of multimeters was known for their robustness, precision and reliability. The AVO model 8 is a very good instrument. In the time it was introduced, its 37.5 μA meter movement made it an exceptionally sensitive instrument. In march 2007 I bought this AVO model 8 that looked very well. The price was low because the meter movement was defective. When I collected the meter, I had a very pleasant conversation with the seller who had worked with different types of AVO meters a lot, and who was pruning his collection of instruments. When I inspected the meter for the cause of the defect, I saw that the counterweights that balance the meter movement, had disappeared. After some fiddling, I was able to make some replacement weights and rebalance the meter. It is now working again. Although I should recallibrate it, it is already a nice instrument to have and use.

AVO model 7

The AVO 7 was a robust instrument, manufactured in the 1950-ies by the British AVO company. Somewhere around 1982 I found this specimen on a flea market. I remember there was a label on it from the local electricity company. It was clear that the meter had been used heavily, because the lettering "DC switch" and "AC switch", engraved in the Bakelite case, had almost worn out. I hoped that this was my chance to own and use one of those a legendary AVO meters and decided to accept its condition. Alas, when I inspected the instrument at home, I found it did not work. There were signs of numerous previous repairs and some of the resistors looked scorched. So this is a nice old instrument to look at, but nothing more. Anyway, the AVO model 7 uses a 1 mA meter movement, so for electronic measurements it generally loads the circuits too much.

Unknown British meter

This is a British made meter I bought on a flea market somewhere around 1980. I don't recognise the name of the company that made it. Judging by its construction (it has an off-the-shelf 1 mA meter movement and standard stock switches in a Bakelite case - no fancy custom case and meter) this must be one of a small series from a small workshop only The meter is still working but the readings are 25 % low on all ranges.

Unigor type 6E

Unigor by Goertz was a brand of robust meters from Austria. I remember Unigor multimeters were used in the electronics lab at the Delft University of Technology. The Unigor 6E is an electronic multimeter, meaning it has a built-in battery-operated transistor amplifier. This results in a sensitivity of 1 MΩ/V and a lowest DC current range of 1 µA. It has 54 AC and DC ranges, 13 dB ranges, 12 resistance and capacitance ranges and 2 temperature ranges (if one has the matching temperature probe). Goertz claims an accuracy of 1% for this meter. It has a mirror scale to enable accurate reading. A very good and professional meter. I bought this meter in 2009. It looks like it is in very good shape, althought the test prods that came with it are not original and the battery compartment is corroded.

M-4324

This is a Russian multimeter that was sold in large quantities in the late 1970-ies as a robust and precise yet affordable instrument for hobbyists. It seems to have been inspired by the Unigor, although it is far less robust. I bought it in 1977 for 69,- Guilders. It has a 40 μA meter movement with a large number of scales. The meter movement uses a taut band suspension instead of a jewel-and-spring. It has separate AC scales to correct for the small errors introduced by the meter rectifier. An interesting feature of this meter is the fact that it uses 3 NiCd cells as a battery for the resistance ranges. This turned out to be a disadvantage rather than an advantage, as there was no battery charger included and the NiCd cells eventually were worn by too frequently charging them. I replaced the button cells by size AA NiCd cells, but these gave up too. I have used this meter for my day-to-day hobby use for a number of years, until I bought a digital multimeter in 1986.

Alecto TM-200

This is a small but useful Japanese multimeter from the late 1970-ies for the beginning electronics hobbyist. It has a 50 µA meter movement and if offers all the ranges that a hobbyist normally needs. This meter was bought and owned by a good friend of mine, who gave it to me when he decided to end his electronics hobby.

Unisound DT-1103

This is quite a remarkable multimeter because of the 10 μA meter movement. Its sensitivity is no less than 100 kΩ/V (10kΩ/V on AC) so that on the 1000V DC range it has a higher input resistance than my DVM. Its size suggests it is a professional instrument, but on the inside it doesn't look really robust. The only references to the Unisound brand I can find on the web, suggest this meter was sold by Radio Shack, which more or less confirms it's aimed at the hobbyist.

When I opened it, I discovered the two size B cells for the ohms ranges had been leaking. The battery holders had rusted, but not too badly. I took the battery holders apart, took the contact springs out and cleaned them. After that I polished them and they ended up looking reasonable.

I bought this meter on a flea market at my children's school in 2006. I did not really need it, but I found its large size and sensitive movement very interesting. Unfortunately, I forgot to take the instruction booklet home. When I ran back, the seller had already left. Anyway, even without the manual the meter is working excellently.