[R-390] Stripping knobs

[Jacques Fortin]

Hi Jim, just my two cents:
I used a pot filled with lacker thinner to strip the R-390/390A knobs.
The metal used to make those is not pure aluminum, but a zinc alloy (zamak) for the small ones and an aluminum based alloy for the tuning ones.
To repaint those, I used Krylon Dual Superbond in black satin finish, because it was the one that best matched the original.

Happy New Year to all !

73, Jacques, VE2JFE in Montreal

Been working on combining several R-390/URR carcass radios into as many complete radios as possible.  I took one set of knobs and put them in full strength Simple Green All Purpose Cleaner as a stripping agent.  It takes some time but it works well.  Once the paint is loose, a brass brush does the work of removing the stubborn spots.  Best to ware gloves as full strength cleaner really dries the hands! Bar Keepers Friend in the powder form and an old toothbrush does a nice job of removing the remaining film and leaves a clean bright aluminum like finish.  Interesting that some knobs had a red primer coat, some had a gray primer coat but most had no primer coat at all.  The internal structure of some of the large knobs is different so evidently there were more then one supplier.
Diluted Simple Green works well to clean the front panel as does Krud Kutter.  I like the latter as it is not supposed to attack aluminum.  There are formulations of Simple Green that are safe on aluminum, better then the standard formulation.  I will try the Simple Green Coil and Condenser cleaner on the next set of knobs, if I can find it!
I looked at the various tips and see that there is no standard recommended paint for the knobs.  The original paint appears to be flat black, I assume that it is an oil based enamel.  Any comments about the use of gloss or semi gloss black?

Happy New Year!
JimLogic: Method used to arrive at the wrong conclusion, with confidence.  Murphy ______________________________________________________________
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