UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - New movement fitted into AVO CT160 meter case

retailer · 11th Apr 2022, 1:17 pm

The meter of my fixer-upper CT160 was in a sad state - the meter case was cracked in the usual spot, the rear glass had come loose and broken while in transit and the coil of the movement was open circuit. On taking the movement apart I could see that a few of the inner turns the coil which is not wound on a former had come loose and had been rubbing on the central pole eventually breaking the wire - it is very fine. With a transplant in mind I found a suitable donor in my meter drawer, the pointer was the right length and the movement itself was a reasonable fit into the CT160 meter case, I just needed to fabricate 2 brackets - one to hold the movement in the case and another to support the original Avo plastic scale, this way I could keep the original appearance of the meter.

Late last year I converted my manual milling machine to CNC and while it is not yet fully finished it is operational so I took the time to measure the CT160 case, the movement and the scale and draw up a 3D model of the two brackets in Fusion360 to be machined in the CNC mill - I did end up machining 3 of each in total, as I had to fine tune the measurements - the 'new' movement fits nicely it's 200uA fsd and needed a meter amp to bring it up to spec at 30uA fsd, the meter amp board tracks were cnc milled - once again Fusio360 was used to design the board and route the tracks. The plan was to cut the PCB to exact size and drill holes in the tester aluminium framing to mount it but it struck me that I could just mount it directly on the meter, there is room for it and turned out to be a good solution - if I had thought of that sooner I could have designed the board so it fitted exactly behind the meter case with no overhang - the PCB is the subject of a separate post in the diy section.

I used fine steel wool to clean up the meter case and soon found one shouldn't let steel wool and meter magnets share the same room - I spent the best part of an hour with a length of masking tape that I rolled into a tube sticky side out and then flattened so it could be slipped down between the central pole and magnet to capture all those fine bits of steel wool.

11th Apr 2022, 1:17 pm	#1
retailer Heptode Join Date: May 2005 Location: Adelaide, South Australia Posts: 541	New movement fitted into AVO CT160 meter case The meter of my fixer-upper CT160 was in a sad state - the meter case was cracked in the usual spot, the rear glass had come loose and broken while in transit and the coil of the movement was open circuit. On taking the movement apart I could see that a few of the inner turns the coil which is not wound on a former had come loose and had been rubbing on the central pole eventually breaking the wire - it is very fine. With a transplant in mind I found a suitable donor in my meter drawer, the pointer was the right length and the movement itself was a reasonable fit into the CT160 meter case, I just needed to fabricate 2 brackets - one to hold the movement in the case and another to support the original Avo plastic scale, this way I could keep the original appearance of the meter. Late last year I converted my manual milling machine to CNC and while it is not yet fully finished it is operational so I took the time to measure the CT160 case, the movement and the scale and draw up a 3D model of the two brackets in Fusion360 to be machined in the CNC mill - I did end up machining 3 of each in total, as I had to fine tune the measurements - the 'new' movement fits nicely it's 200uA fsd and needed a meter amp to bring it up to spec at 30uA fsd, the meter amp board tracks were cnc milled - once again Fusio360 was used to design the board and route the tracks. The plan was to cut the PCB to exact size and drill holes in the tester aluminium framing to mount it but it struck me that I could just mount it directly on the meter, there is room for it and turned out to be a good solution - if I had thought of that sooner I could have designed the board so it fitted exactly behind the meter case with no overhang - the PCB is the subject of a separate post in the diy section. I used fine steel wool to clean up the meter case and soon found one shouldn't let steel wool and meter magnets share the same room - I spent the best part of an hour with a length of masking tape that I rolled into a tube sticky side out and then flattened so it could be slipped down between the central pole and magnet to capture all those fine bits of steel wool. Attached Thumbnails