01-05-2015, 03:42 PM
http://golbornevintageradio.co.uk/forum/showthread.php?tid=4523&highlight=monoknob
Some while ago I asked if anyone had any chassis with Volume and Tone pots on them that might be of use. I did find a couple of chassis but the items were no better than on mine. I'm convinced that all are probably now of no use. Apart from being noisy (on a signal gennie and headphones) they have gone out to roughly 3 times there original value. That is a 600K at 1M6 and use WD40 and it goes to 1M8.
These pots are Philips clever design again having a 5:1 gearbox (multiplied to about 8:1 by the position of the fulcrum on the operating lever) built in.
Anyway a nice man on ARM suggested, and gave me a sketch of an idea to use external gearbox's to drive new conventional pots. I doubted that without a lathe I would be able to make these but once I found suitable gears started to see it was possible using just my column drill. This was needed to shorten spacers and cut shafts. But putting them in the drill and pulling them down on a file does the job. Lots of ins and outs and measuring but I can get within 1/10 of a mm.
So pots are now working smoothly and I can proceed with the rest of it: rewire the chassis, get a rewound bandpass coil and finish the artwork for a new dial, probably a difficult re-alignment and then a cabinet restore in the summer.
Happy to have solved a major issue.
Gary
Some while ago I asked if anyone had any chassis with Volume and Tone pots on them that might be of use. I did find a couple of chassis but the items were no better than on mine. I'm convinced that all are probably now of no use. Apart from being noisy (on a signal gennie and headphones) they have gone out to roughly 3 times there original value. That is a 600K at 1M6 and use WD40 and it goes to 1M8.
These pots are Philips clever design again having a 5:1 gearbox (multiplied to about 8:1 by the position of the fulcrum on the operating lever) built in.
Anyway a nice man on ARM suggested, and gave me a sketch of an idea to use external gearbox's to drive new conventional pots. I doubted that without a lathe I would be able to make these but once I found suitable gears started to see it was possible using just my column drill. This was needed to shorten spacers and cut shafts. But putting them in the drill and pulling them down on a file does the job. Lots of ins and outs and measuring but I can get within 1/10 of a mm.
So pots are now working smoothly and I can proceed with the rest of it: rewire the chassis, get a rewound bandpass coil and finish the artwork for a new dial, probably a difficult re-alignment and then a cabinet restore in the summer.
Happy to have solved a major issue.
Gary
