08-04-2021, 01:14 AM
That American Bosch is a GREAT old radio ! Do NOT try to power it up until you have pulled the chassis and checked to see that all paper condensers and electrolytic condensers have been replaced, all the resistors checked to make sure they are in spec, and replaced if necessary. Then test all the tubes and replace those which are bad or weak. Once that is done, then you can power it up on a variac. If you are very sure of your work you could even just plug it in and see what happens being careful to feel the power transformer and watch the plates of the rectifier tube for overheating, which is what I mostly do, though not the recommended approach.
Now, you may wonder why we replace ALL the paper condensers and electrolytic condensers. It is because they are either bad already, or soon will be, and they can fail in a shorted condition which can cause damage to things like the power transformer which is VERY EXPENSIVE to get rewound, if you can even get it done. They can also cause a fire hazard. Best to just replace them all and be done with it.
Looking at the schematic http://www.nostalgiaair.org/Resources/773/M0040773.htm I see that there are a couple of condensers across the power input to ground to filter out line noise. This was VERY common on these old sets, Philco, RCA, Zenith and others did the same. These should be replaced with a type Y safety condenser, the kind that FAIL OPEN.
I envy you this latest acquisition. It is going to be a great project, and you will both learn a lot and have a lot of fun. Be very patient. Take your time. You will end up with a fine, reliable radio you can be proud of, and which will still be working fine years and years from now. I look forward to your thread detailing your progress in the restoration.
As for that, TAKE LOTS OF PICTURES ! It is so much easier now that we have cheap digital cameras. Take them before you start ANY work so you have a record of how things were to begin with. Then take more pictures along and along as you work, documenting each thing you do. You'll find this can be invaluable if you want to check things. Also, you will have pictures to post in your restoration thread. About posting pictures... If you first post them to a picture posting site, and then use the link to that photo to post the picture in your thread here, you will find that it will load much quicker when people check the thread. You can use any of the picture posting sites. I use tumblr. Good luck, and feel free to ask any questions you may have.
Now, you may wonder why we replace ALL the paper condensers and electrolytic condensers. It is because they are either bad already, or soon will be, and they can fail in a shorted condition which can cause damage to things like the power transformer which is VERY EXPENSIVE to get rewound, if you can even get it done. They can also cause a fire hazard. Best to just replace them all and be done with it.
Looking at the schematic http://www.nostalgiaair.org/Resources/773/M0040773.htm I see that there are a couple of condensers across the power input to ground to filter out line noise. This was VERY common on these old sets, Philco, RCA, Zenith and others did the same. These should be replaced with a type Y safety condenser, the kind that FAIL OPEN.
I envy you this latest acquisition. It is going to be a great project, and you will both learn a lot and have a lot of fun. Be very patient. Take your time. You will end up with a fine, reliable radio you can be proud of, and which will still be working fine years and years from now. I look forward to your thread detailing your progress in the restoration.
As for that, TAKE LOTS OF PICTURES ! It is so much easier now that we have cheap digital cameras. Take them before you start ANY work so you have a record of how things were to begin with. Then take more pictures along and along as you work, documenting each thing you do. You'll find this can be invaluable if you want to check things. Also, you will have pictures to post in your restoration thread. About posting pictures... If you first post them to a picture posting site, and then use the link to that photo to post the picture in your thread here, you will find that it will load much quicker when people check the thread. You can use any of the picture posting sites. I use tumblr. Good luck, and feel free to ask any questions you may have.
