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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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20th May 2014, 9:22 pm | #1 |
Retired Dormant Member
Join Date: Feb 2011
Location: Auckland, New Zealand
Posts: 12
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Backoff pots on AVO VCM Mk4
The backoff pots on my Mk4 valve tester have become rather scratchy, so I think they would benefit from some Cramolin. The problem is how to get the juice into them - they appear to be almost sealed units so the back cans are going to have to come off. Given they are buried deep within the tester, the only way I can see of achieving this is by removing the pots - here's where the plan becomes unstuck. Knob removal is easy, then one is confronted with a roll pin through the shaft, which really does not want to be moved. Any ideas how this can be done without special pullers (pushers?), or alternatively, any better ways of getting contact cleaner into the pots?.
M |
21st May 2014, 12:24 am | #2 |
Octode
Join Date: May 2009
Location: Linkoping, Sweden
Posts: 1,463
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Re: Backoff pots on AVO VCM Mk4
If you look carefully at the roll pin you should be able to see that one end is straight and the other has the edges filed down a small amount so they could slip into the hole easier. You need to push the pin out towards the straight end. On some shafts one end of the hole is larger, having a conical opening, this is the end that the pin should come out of and also inserted into.
You can use a piece of wood or pcb and put it against the shaft for protection and then use a pair of heavy pincers to push the pin out, put one claw of the pincers on the piece of wood and the other on the roll pin and then just squeeze the pincers, the roll pin should come out quite easily this way. Some roll pins are conical so one end is smaller than the other, I have seen both types of roll pins on AVO VCM's. It is possible to replace the potentiometers by buying new Clarostat potentiometers and then either swapping the shafts or cutting the shaft and drilling a new hole for the roll pin. You will have to grind down one side of the shaft socket and also replace the slider, cutting it from the new potentiometer and then soldering it on the old slider, if you swap the shafts.
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Martin, Sweden |