40-190 hums intermittently - Printable Version
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RE: 40-190 hums intermittently - codefox1 - 07-25-2013
You are lucky to not have turned this one into a basket case. Don't turn it on again until all the electrolytic and paper capacitors are replaced with recently manufactured stock. A good cleaning of all switches and controls would be wise, and some of us just replace all the small carbon resistors whilst doing the overhaul because it is easy enough, cheap, and makes a big difference in alignment accuracy and long term reliability. Strange as it might seem, the tubes are pretty hardy.
RE: 40-190 hums intermittently - Raleigh - 07-27-2013
I think the 40-190 has a couple of can electrolytic capacitors mounted on the top of the chassis. They are almost certainly bad, but can be cut open and modern electrolytic capacitors mounted inside them (called restuffing.) This preserves both the appearance of the radio and the original under-chassis wiring. Some restorers like doing this, but others don't and just mount the replacement electrolytic capacitors in some convenient place under the chassis. You might need to add a terminal strip underneath.
The antiqueradio.org web site recommended by Klondike98 has a page on restuffing electrolytic capacitors if you should have any interest in it.
By the way, if you don't restuff the two topside capacitors, you should not connect the positive side of the old capacitors to anything at all. The negative side of the old capacitors can be used to make mounting of the new ones easier, but be aware that one of them is grounded to the chassis and one is separated from the chassis with a fiber washer.
RE: 40-190 hums intermittently - codefox1 - 07-28-2013
Yup, compared to a 65 year old cap, a 25 year old cap looks "new." Most likely still bad or about to fail. You'll have to undo the hatchet job, but take plenty of pictures.
I'd replace the carbon resistors as well for long term reliability at the same time you change the capacitors. Easy enough and inexpensive.
RE: 40-190 hums intermittently - fossilexpress - 08-01-2013
Almost ready to order the replacement caps and resistors and restore this thing. With 5 exceptions, all of the caps are original. Some of them look like they are getting to be tricky to get to. In lieu of multiple posts, here are some questions I still have:
1. As I replace components, should all leads be covered with heat shrink tubing? What should I use as a heat source?
2. Should I remove the tubes prior to servicing?
3. If I want to clean the chassis and other components (e.g., tuning condenser), are there best practice tools and products? (BTW, I have a copy of Johnson's book)
4. Looking at pictures of other 140-90's on this site, the antenna is covered by some sort of cardboard (?) tube. The repair sheet describes it as "shielded" Should I make one? Out of what?
5. One of the "new condensers" is .01 mf, 1600v (I think this is no. 52). One of the old ones is 0.003 mf, 1000v (number 50). Should I use 1600 v replacements for both?
6. And finally, any common beginner mistakes I should watch out for?
If any of you are at Radiofest, enjoy visiting the Chicago area! - Thanks in advance - Roy