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 Post subject: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: Dec Sat 15, 2018 7:59 pm 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
Hello All,

I'm putting together an order for the above referenced receiver and I have a couple questions:

1) This is the first time I have worked on a receiver this new and there are a couple types of caps that I don't recognize and wonder if I should replace them. The first type is a ceramic tube with sealed ends, no way to know what is inside. The second type appears to be rolled foil in a clear injection molded body. I have attached pictures for both. Any opinions on whether or not I should replace these along with the wax caps?

Attachment:
File comment: Ceramic Tube
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Attachment:
File comment: Injection Mold
DSCN1165.JPG
DSCN1165.JPG [ 75.35 KiB | Viewed 776 times ]


2) My copy of the SAMs Photofact isn't clear enough to see if there are any wax capacitors in the FM module. I would prefer not to disassemble it because I'm afraid I'll get in over my head. Have any of you been into one of these? Is there any caps that need replacing in that sub-assembly?

Thanks in advance for your replies,
Russ Mileham


Last edited by rmileham on May Sun 10, 2020 12:57 am, edited 1 time in total.

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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sat 15, 2018 9:40 pm 
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Location: Annapolis, MD
If i am not mistaken, those ceramic tubes have P/W caps inside. The smaller silvery-looking ones(eg second picture) look like film.
The universal rule of capacitors: If in doubt, replace.

FM module:
I always open such things for cleaning and inspection (eg coils whose mechanical connection has come loose)
I normally don't find much to replace but, in principle, there could be a small electrolytic hiding in there. If you prefer not to open it, then post a snip from the schematic so we can see what is likely.

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"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sat 15, 2018 11:11 pm 
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Joined: Nov Fri 15, 2013 10:17 pm
Posts: 2038
Location: Haddon Heights NJ
My two cents:
I have only repaired a handful of "modern" radios, but i fund that the only electrolytic need replacement. I'm guessing for the pictures that this is a 60's model, at least looks from that era to me. Any way, in my very limited sample i think i only changed 1 "wax" cap, solely because was physically damaged.

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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sun 16, 2018 12:57 am 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
Mark,

Paper and Wax so should probably replace, got it.

I am 99% certain that there are no electrolytic caps in the FM sub-assembly for two reasons: 1) in looking at the schematic, all caps have values on the order of picoFarads. Too small for 'lytics? 2) The photo fact separates out the electrolytic caps in the parts list and I have accounted for them all in the main chassis.

Do the small values indicate that they are most likely ceramic disc? I'm really nervous about taking the sub-assembly apart. I really want this stereo as a daily driver and would hate to screw it up.

My pdf viewer doesn't seem to have an easy way to take out a snippet, I'll keep trying.

Dan,

You are exactly correct about the radio being a fairly late mode. It is about 1963 or 64. I showed some pics when I first got it here: http://antiqueradios.com/forums/viewtopic.php?f=9&t=309178
I hear what you're saying about the electrolytic caps, but I'd really like to replace the wax and paper caps too while I'm in there. There are a couple in this chassis that are bubbled and at least one has been dripping wax. I won't replace any of the ceramic disc caps unless I find one I know to be bad.

Thanks for the replies!

Best,
Russ


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sun 16, 2018 2:26 am 
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Quote:
Paper and Wax so should probably replace, got it.


In general, for the radio you're working on, anything that's shaped like a AAA battery or larger, it's paper or electrolytic; those are clearly distinguishable in your photos. On the schematic, anything larger that about 1mfd and has polarity markings is probably electrolytic.

Quote:
Do the small values indicate that they are most likely ceramic disc?

Any in pico range, it's not likely paper, leave it in place.


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sun 16, 2018 3:41 am 
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Location: Annapolis, MD
Quote:
My pdf viewer doesn't seem to have an easy way to take out a snippet, I'll keep trying.
Use a photo editor. If you have a Windows system, I'm pretty sure there is one there by default. One popular freebie is Irfanview.

I us GIMP, which is almost as powerful as Photoshop, but is also free.

BUT--I believe you about no electrolytics in the FM module---maybe you want to save this for later.

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-Mark
"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever
PostPosted: Dec Sun 16, 2018 5:04 am 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
Attachment:
GimpSnip.jpg
GimpSnip.jpg [ 56.22 KiB | Viewed 725 times ]


Thanks for the tip about GIMP Mark. It seems to work well with Lubuntu which is the OS I have on this old laptop. I think for now I am going to try to avoid the FM module. Once I have finished recapping the main chassis I will worry more about it during testing and trouble shooting.

Best,
Russ


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: May Sun 10, 2020 1:09 am 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
Hello All,

I have finally gotten back to this receiver, please don't judge. I have recapped, troubleshot an FM oscillator problem and have it working pretty well after aligning both the AM and FM sections.

The problem I have is that FM sounds great as long as I leave it in mono, but selecting FM Stereo introduces noticeable distortion . I also noticed when I tried to align the mulitplexer that adjusting the 67 kHz coil had no discernible effect.

Any thoughts on where I should look first?

Thanks,
Russ

Attachment:
Multiplex.jpg
Multiplex.jpg [ 121.93 KiB | Viewed 354 times ]


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: May Sun 10, 2020 3:51 am 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
I think I found it.

R53 and R54 form a voltage divider to supply 30V to pin 9 of the 6CL8A. R53 was open and R54 was out of spec. I replaced both and FM Stereo sounds much better.

Russ


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: May Sun 10, 2020 11:42 am 
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Joined: Nov Fri 15, 2013 10:17 pm
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Location: Haddon Heights NJ
Nice, FM alignment is much more involved than AM. The IF transformers need to peeked in a certain way as they need to pass a bigger signal. I normally use a scope and a signal generator with markers.

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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: May Sun 10, 2020 1:13 pm 
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Joined: May Thu 21, 2015 4:15 am
Posts: 292
Location: Brookings, SD
Hi Dan,

I learned that with this project. It was my first attempt at an AM FM Stereo. I used a sweep generator without markers. I tried to inject a marker from a second generator. It was all very haphazard, but I think it worked ok. My big problem was a noisy scope trace and the sweep generator had some drift.

In spite of all that, the radio sounds good and the sensitivity seems acceptable. After making the repairs to the multiplexer FM Stereo sounds much better, but I can still hear a hiss at higher volume and on weaker stations. Perhaps I should go through the alignment of that part of the circuit again.

I'm also thinking that if I'm going to make a habit of working on these things, I need some better equipment. Many times I felt like I was trying to do brain surgery with a hacksaw.

Russ


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 Post subject: Re: RCA Victor RC-1205C AM FM Reciever - New Question
PostPosted: May Sun 10, 2020 5:37 pm 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 124
Most of the tube type multiplexers I have heard never sound as good as the solid state ones. Alignment may help, but it may be as good as it gets. Old stereo instruction books even say to switch to mono if the sound is noisy on weaker stations, some units did this automatically.


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