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This topic comprises 2 pages: 1 2
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Author
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Topic: An old RCA tube amplifier?
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Doug Eisemann
Film Handler
Posts: 21
From: Douglassville, PA
Registered: Mar 2001
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posted 01-03-2005 04:44 PM
Hello, Fixing amplifiers like this is what I do for a hobby and a job, so I could offer some pointers. First of all, I can't find any literature in my files on this particular model, but I have seen them before, and I know they can actually be very good sounding amps. I have the 1939 model MI-9355, using 2 845 output triodes and 2 866A mercury rectifiers. It needed a smaller power amp (15-20 watt MI-9354) to drive it to full output. Part of the PG-142 system I believe. On your amp, it is likely that any electrolytic capacitors will be beyond useful life at this point, and need to be replaced. Small paper capacitors may or may not be good at this point. Whatever you do, don't just hook up power to it and turn it on. Things may be irreversibly fried that way. The person at Radio Shack is unlikely to know much about fixing it, unless he is used to tube gear, but it should certainly be able to work again with some component replacement. All tubes are still available, except old 2A3s are expensive, but new ones are being made. Feel free to email me if you need some more help
Thanks Doug Eisemann [ 01-03-2005, 04:55 PM: Message edited by: Brad Miller ]
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Doug Eisemann
Film Handler
Posts: 21
From: Douglassville, PA
Registered: Mar 2001
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posted 01-03-2005 07:35 PM
I wanted to add to Mr. Gulbrandsen's post about replacing components. If you do have to replace components to make the unit functional, I always try to use modern replacements, carefully hidden in the old cases. IE, often with electrolytic capacitors, it is possible to cut open the old case, remove the old internals, and place the new, smaller part inside. When reassembled carefully, it is hard to tell anything was done. It is nice to see these units restored carefully and enjoyed, rather than simply sold off due to their monetary value. Generally, the build quality of old theater amplifiers is better than any new "high end" audiophile tube stuff, and cost a fortune when new, hence the high value even today. It will be interesting to see your progress.
Best Regards Doug Eisemann
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Will Kutler
Phenomenal Film Handler
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Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001
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posted 01-06-2005 01:01 AM
I agree with what many people have said on this forum.
Usually resistors and wax-paper caps go bad and must be replaced. Just install the new ones exactly as the origonals were.
If those origonal can-style electrolytics are bad, and no new ones can be found, a simple solution is just to disconnect the leads, install insulated terminal caps, and then just install a new modern cap between those disconnected leads....or like what was stated, remove the guts from those origonal caps, put the new cap inside, and reinstall onto the chassis.
Check out Antique Electronic Supply in Scottsdale, AZ for your needs. You may also take a look at Antique Radio Classified magazine.
Changing the subject, I finally aquired a radio at a very reasonable cost that I have been searching for for several years....the 1938 RCA 816K, and am looking forward to beginning restoration!
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