Avometer Terminal Post Replacement

Repairing the terminals of an Avometer can be a tricky process because finding replacement posts can be extremely difficult. Avo meters for sale on eBay often have, missing, broken, and even burnt terminals, and in this article, we look at replacing them. Interestingly, this part has many different names, for example, the service manual mentions them as "non-loss terminals". However if you want to buy on eBay, then it goes by the name "binding post". They are more popular for use with connecting speakers; however, there are also ones for connecting power supplies. The ones that have a chance of working for the Avometer is the "long screw" type, hence you need to search for "long screw binding post" on eBay.

The posts screw into an embedded brass collar with a thread. This forms an airtight connection that isolates the electronics from the outside environment, thus ensuring military specifications.

The length of the top pair of posts have to be 33 mm long with 6 mm diameter, however the bottom pair can be shorter and you may get away with 20 mm long posts.

On the Avometer Mk 1 and Mk 2, the top pair of terminals are for 2500 V ranges, whilst the bottom pair are for the switched ranges. These terminals are for carrying high voltages and currents, and the top pair of terminals must be the correct replacement part, capable of handling high voltages and current. Do not use binding posts intended for speakers as they are for low voltages and currents and may melt.

If you are using the meter for hobby use, chances you will never use the 2500 V range terminals, and people often use those to replace the bottom pair. This option will allow you to use the meter without costing anything.

Maplin JK24B Twin Terminal Posts – Binding Posts

The Maplin binding posts, code JK24B, seemed like they had a good chance of fitting. The diameter of the posts is smaller and therefore they will not screw onto the existing threads, however they will fit through the hole and the supplied nut and washer can secure them from the other side.

There is only one small modification required to the posts, which is to the small rectangular step. I had to file away approximately 3 mm from either side so that it would pass through the hole. The posts are made of brass, which is soft, and therefore a small hobby craft file was enough to file a part of the step away. However, as the man says, "You break it. You bought it."

Once you file that little step off, it looks like this.

As you can see, it fits nice and flush now, and all I need to do is to secure it with the supplied nut and washer from the other side.

In this photograph, I have secured it tight with a nut and washer, and soldered the wire directly to the post. You will need to use a high wattage soldering iron to solder onto the brass post but it is very simple and easy.

Terminal Caps

On occasion, the metal terminals will be fine and only the caps have melted. In the service manual the black terminal cap is part number 10/6/8, and red the terminal cap is part number 10/7/8.

Back then, AVO Ltd supplied even the replacement terminal caps, however, today it is difficult to find this part.

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