[R-390] Front Panel Restoration Knobs Rock Tumbler

[Glenn Scott via R-390]

Cecil and group,


Sorry about the last title line????



I have tried glass, hulls, and several other media's on these panels. Nothing came close, especially, with rapidly cleaning out the letter engraves while not doing ANY damage to the front panel whatsoever. Once the flow and pressure are dialed in, I can do one side of a panel in about 5 minutes or less with no subsequent picking of paint and primer from the engraves. The Armex powder pellets are small and get deep into into the engraves much better than anything else I have tried.


For the knobs, I use a large rock tumbler with 2 gallon drums with the green pyramid media I get at Harbor freight. I put 3 or 4) R390 or A sets in the tumbler and let it spin about 2 weeks. Sometimes, I have to put a few knobs back in for another 2 weeks but I keep enough spare knobs ready to keep up with and exceed my  restoration needs. I have not seen any rounding of corners or other issues with the tumbler.
After the green pyramid treatment, I swap jugs on my tumbler and spin the knobs with hulls for another 4 or 5 days. They come out very clean and ready for Powder coating after a quick dip into my Acetone tank to remove any oil from the hulls. 


I bought tapered silicone plugs to shove into the holes on the bottom of the knobs to keep chunks of media from clogging them. The plugs are especially needed for the large MHz and KHz knobs. If you don't plug those holes, there is a chance of breaking  off the fingers on back.


Can we post links on this forum?


http://www.ebay.com/itm/186-piece-High-Temp-Silicone-Rubber-Powder-Coating-Tapered-Plug-Kit-MIT-PK-186-/261872974999?hash=item3cf8d87c97&item=261872974999&vxp=mtr


The plugs were cheap, reusable and color coded. You can get them at companies that sell powder coat supplies and on epay.
I have some worn out, sacrificial, Bristol set screws that I loosely install in the set screw  holes to keep the media out as well.


Unless the Bristol screws are perfect I replace them with the EXCELLENT screws that Dr. James A. Moorer sells on epay. I bough a substantial number of these from Dr. Moorer and they are of OUTSTANDING quality. He had these PROFESSIONALLY machined a number of years ago and this has been a wonderful resource for all of us who enjoy these receivers; his ebay name is jamminpower. As most R390 series receiver enthusiast know, Dr Moorer has an excellent website that has loads of R390(A) information.


I like using the tumbler since it's working 24 x 7 and does not take away from my bench, play or rest time. I tried a vibrating tumbler from Harbor freight which worked well, maybe a little faster than the rock tumbler but after a month the HF unit started to fall apart. HF did give me a refund which I used for more media.
The tumbler I bought was about $300 and has a large heavy duty motor; the additional jugs were ~$35 each. I have used it for the last 3 or 4 years and it's still running with no problems.


73,
Glenn Scott WA4AOS
DSM Labs
glenn at dsmlabs.com