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 Post subject: RCA Victor RHC60W Solid State Stereo line noise issues ...
PostPosted: Jan Thu 11, 2018 3:08 am 
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Joined: Oct Tue 13, 2009 4:10 pm
Posts: 108
Location: Alexandria, VA
Greetings all:

This question concerns an RCA Victor RHC60W (chassis #RC-1227A) AM/FM/FM Stereo table radio from 1966 with Phono and Tape inputs. This radio plays quite well with nice fidelity after I replaced all of the electrolytic caps in the power amp and tuner sections. However, there is a constant loud static / hissing noise that occurs regardless of volume setting and regardless of what input function is selected.

Looking at the 2 snippets of the schematic below, I would like to get some information about the capacitors C76, C77, C78 and C79. These caps are right after the plug, and I'm assuming they are used for line noise supression.

Attachment:
RCA Schematic snippet1_smaller.jpg
RCA Schematic snippet1_smaller.jpg [ 87.64 KiB | Viewed 1268 times ]

Attachment:
RCA Schematic snippet2.JPG
RCA Schematic snippet2.JPG [ 15.64 KiB | Viewed 1268 times ]


Two of the .01 capacitors are missing from my chassis, and there is evidence of a mini-explosion that occurred at some point in the life of this radio. It is also evident that someone did a quick fix job that bypasses the 2 missing caps (C79 is still in place, as is one of the .01 caps). The fix was crude but it does allow the set to work...

My goal is to re-wire this front section to include all of the caps that should be there. I have a non-working parts chassis from another similar stereo (chassis #RC-1227C) that has all of the capacitors in place and wired as they were in the factory, and using this as a template and my schematic, I want to restore this section to its original spec.

My questions to everyone are:
1. What should the voltage ratings be on these .01uf capacitors? As you can see, the voltage ratings are not listed on the schematic. My parts chassis has one large .01 cap with a rating of 1000V on the cap, but the 2 small .01 caps do not have voltage ratings listed on them.

2. The voltage rating on these caps would have to be for AC current and not DC, right? If that is the case, I'm not finding these AC caps when I search on Mouser.com and other sites. I have found some high-voltage caps on Amazon, but the specs don't tell you if these are for AC or DC current. Can anyone direct me to some replacement caps?

3. I haven't found a cap that is 470pf @ 1.4 KV, but I have seen some that are 470pf @ 2000V (although again, I'm not sure if they are for AC or DC current!). A higher voltage rating should be OK, right?

Thanks so much for your assistance!

Stan


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Jan Thu 11, 2018 1:03 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17969
Location: Utica, NY 13502 (USA)
Since you said the static and hissing noise is there regardless of volume setting, are you sure the problem is, indeed, line noise?

Dave


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Jan Thu 11, 2018 4:12 pm 
Member

Joined: Oct Tue 13, 2009 4:10 pm
Posts: 108
Location: Alexandria, VA
Hi Dave,

No, I don't know for sure that this is the cause. I did think putting the circuit back to specs would be a good idea anyways...

Is there another purpose for the caps than what i thought they were for?

Any advice would be helpful. :-)

Thanks,
Stan


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Sep Sat 12, 2020 1:13 pm 
New Member

Joined: Feb Sun 17, 2019 8:34 pm
Posts: 8
Hello Stan,
I also have nearly the same chassis, RC1227C, which went inside an MJT60W. The exact same thing happened to me and those same small ceramic caps! I also have the same schematic and to me the problem stemmed from the phono unit. Those caps bridge across power supply and switching mechanism for the phonograph. I wonder if your rca record player caused the issue. I suspect my turntable motor may be the culprit here.


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Sep Sat 12, 2020 4:58 pm 
Member

Joined: Dec Mon 23, 2019 5:52 pm
Posts: 267
Those caps in the AC input circuit helped stop the "pop" you would hear when turning the power switch or the record changer on and off. Since two of them are across the AC line all the time it wasn't unusual to find them blown up, may even happen when no one was around to hear it. I think the original Sprague ceramic ones were only rated at 500 volts, the one across the transformer secondary carries the same part number as the primary ones. The hiss or static is caused by leaky germanium transistors before the driver transformers, again, a common problem with these chassis.


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Sep Sat 26, 2020 1:06 pm 
New Member

Joined: Feb Sun 17, 2019 8:34 pm
Posts: 8
RCADanny,
Thanks for your quick reply back on this chassis. I was trying to replace the little stereo beacon light and got an interesting reading of voltage.

The stereo indicator lamp terminals shows either 60V or 62V (depending on whether there’s stereo or not. Currently I have it hooked up to an 8v LED I bought from Dave Wojnarowski. Not sure if it’s supposed to work this way, but the light stays on all the time and then goes brighter during stereo. Someone said the original LeeCraft 3600 (RCA 115635) might have had a step down resistor inline and inside the housing.

Might this be an FM alignment issue, in your experience? The diagram shows approx. 21V on this circuit but looks to have a filter resistor to step down.


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 Post subject: Re: RCA Victor RHC60W Solid State Stereo line noise issues .
PostPosted: Sep Sun 27, 2020 3:07 am 
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Joined: Dec Mon 23, 2019 5:52 pm
Posts: 267
I've never found any resistors in those housings when I've replaced the bulb. I used the 12 volt Radio Shack "grain of wheat" type bulbs. I have also used LEDs but had to change a resistor value and add another. I replaced the 470 ohm connected to the terminal that the bulb connected to (stake #AN) to a 1200 ohm, and added a 330 ohm across the LED. At least those values worked with the LED I used.


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