Johnson Scrubbing bubbles and a small paint brush will get the accumulated dust and surface dirt off the chassis. Wipe with paper towels. DO NOT USE ARMOR ALL WIPES, or anything abrasive. Most polishes have some abrasive qualities to them. Metal polish can be used, but leave the areas around lettering alone. The lettering is fairly fragile and will come off with light rubbing. The serial # is stamped into the chassis with punches. So it won't come off.
Dilute 50parts water to 1 part Simple Green is ok to clean chassis if the scrubbing bubbles doesn't do the trick. The routine here is to use the LEAST HARMFUL and work up to a positive result using the Least Harmful method. So there isn't a "all in one" method of cleaning. Some guys will go to the extreme of Machine polishing the chassis to a chrome like finish and add lettering back on the chassis. FISHER built the chassis as a clean metal chassis with cadmium plating. Yellow dust on the chassis is the cadmium breaking down. Wet it down with water and wipe up. Put it in the bag and seal it. Then go wash your hands as cadmium can be toxic to humans. Wearing gloves (surgical type) is a good idea. Don't try to buff it down to a chrome like finish. Just clean it up and polish it a little to get the 50-60 years of accumulated dust and dirt off.
After you get the cleaning liquids off, blow it down with Hi pressure AIR. Can's of air won't do it. Then let it sit near a heater (air flow is a plus) for a couple days. If it's warm and sunny, put it in the sun.
Now the fun begins. Testing and reconditioning. The Best all around beginner kit is the upgrade kit by Metalbone.
http://www.metalbone.net/fisher.html
However it does NOT come with Multi-Section Can caps, and possibly upgraded grid return resistor values, upgraded Coupling cap values, screen stability resistors, and a way to adjust the bias. (2 boards have been developed on AK and work well for this.). But the Metalbone kit has correct manual, extra schematics for marking up, etc.
HAYSEED HAMFEST
https://hayseedhamfest.com/collections/audio/products/fisher-500-b-re-cap-kit has 2 CAN CAP kits available for the 500B. One has 2 discrete BIAS caps for those who rather build the bias section with discrete parts. The other has a drop in replacement for the dual bias cap. I would recommend the 2nd option as I get the impression this is your 1st reconditioning of a FISHER. Plus it's a neater installation.
If you run into problems, ASK QUESTIONS HERE! The aggregate knowledge base here is as good or better than any other Forum, plus you have dedicated FISHER Hobbiest's here. We pretty much know these units as well or better than the original group of engineers. When you get done with it, it'll be better than it was when you got it, and your grandkids will have a unit they can depend on.
