Steve Green NEPA said:
What are the prerequisites? Temperature? Humidity? Limiting cigarette smoke (the wife is a heavy smoker)? The phase of the Moon? Camphor balls? Spraying the controls? Using them often?
Which, if either, is worse : cold or heat?
I know that car radios weather most weather. Perhaps they're designed to be sturdier. And I've seen two Hammarlund SP-600's that stayed in outdoor shacks for decades of every extreme of weather imaginable which still worked dynamite. I *don't* think those shacks were climate controlled but could be mistaken.
Am just looking to get a few extra miles out of these analog things. To this codger, the analogue ones have more soul.
Engineers? DX veterans?
Temperature - heat is probably worse than cold - heat will deteriorate many components. Room temperature is definitely a good idea. Temperature cycles - hot to cold and back will accelerate mechanical failures and if the radio is based on an IC, help moisture to seek into the IC destroying it. Room temperature is a good idea.
Humidity - can promote corrosion and mold.
Cigarette smoke is horrific for electronics. Some components are corrosive to metal, and others coat the board with a slightly conductive coating. Of course radios are not as important as your wife. Save her life - get her off the things!
I'd keep clear of camphor - but many old radios have a fair amount of flux on the PC board. If you decide to do a cleaning - I would use nothing stronger than alcohol, try to get the 90% pure variety or you will put a lot of water on the board. Do not get it into things like the tuning capacitors, and some early plastic capacitors are sensitive to alcohol damage, so be careful! Test everything. Audio amps are a little different, I take the boards out, soak them in alcohol, brush them with gentle brushes until the alcohol rinses clear. Then I re-assemble and go on my way.
Some people swear by re-capping, if your radio is over 30 years old it may not be a bad idea. Aluminum electrolytics have improved since the 60's and 70's, driven by calls for reliability from switching power supply makers. You can almost certainly get a capacitor in a smaller package and / or higher voltage rating than the ones you replace. Don't sweat things like putting a 47uF 35V in place of a 50uF 15V. It will work!
Do not attempt re-transistoring of old radios unless you have exact (or close) replacements. The 0.1v to 0.2V drop of Germanium transistors is 0.6V of Silicon transistors - the Silicon will not work. Most old radios use PNP and not NPN. I have purchased some junk, non-functional old electronics just to mine them for old transistors so I have stock of them to repair old equipment.
I have a very controversial, but effective way of fixing old switches and pots. I disassemble and clean with solvent, carefully get rid of tarnish with a pink eraser - a good one with small grain size. Its mild abrasion cleans the tarnish right off without scraping off the plating. After I have them completely clean, I put a very thin coating of silicon wheel bearing grease on the contact points, including the resistive wafer of pots. I put them back together, restoring a bit of tension in spring contacts, and that is the last problem I ever have with them. Some that were horribly scratchy are going on 30 years since I did this, and haven't given a problem since. The reason this works is that the grease forms a corrosion barrier, and the spring contacts in the pots and switches have just enough force to punch through the grease, then it wicks back when the pot or switch is moved.
Of course keeping them away from dust is important, if you use something in a dust storm it is going to get inside. If the pots aren't sealed - if the tuning cap isn't sealed, you are looking for problems.
I've got a house full of radios - a lot of transistor radios 50 years old. All work, all are similar in performance to new.
Don't over align, either, do the job right and leave it for at least a couple of years. These things don't drift.
Don't drop them.
