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I_AM_CANADIANOffline
Post subject: RCA stereo console repair  PostPosted: Apr 26, 2014 - 09:51 PM
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My mother has a Canadian RCA Victor stereo console, model no. SCH878. I assume it was made in the early 1960s, and it has 4 speeds, 16, 33, 45, 78, and AM and FM tuners.

Now, maybe 8-10 years ago, I switched it on and played an old 78 on it, and it seemed to work fine. Now, however, as soon as I turn it on and the tubes warm up, there is a loud buzzing that is the same no matter what I do with the volume (buzzing is actually audible even before the tubes warm up). Also, touching the metal parts on it results in a relatively mild shock.

Though I know only slightly more than nothing about electronics, that led me to suspect that it was a grounding problem, but grounding it from the screw labelled 'G' produced no effect. Not sure what the 'A' screw is for. Confused

Judging by what I've read on the internet, the constant buzzing is indicative of bad caps, but I'm a total novice and would rather see a manual or a schematic before I do anything. Unfortunately, Google has completely failed me, I haven't been able to find any reference whatsoever to this console. Might any of our Canadian members be able to point me in the right direction?

And does anyone have any advice as to what the problem might be? My family has only been on this continent for about 60 years, so this is one of the closest things we have to an heirloom, as sorry of a state as it's in. Laughing Many thanks in advance to you groovy, knowledgeable individuals.








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stephenjayeOffline
Post subject:   PostPosted: Apr 27, 2014 - 06:33 AM
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First off, those two terminals marked "G" and "A" are for an external antenna.

As for the loud hum, there's a 90% chance it's a capacitor gone bad. I searched your console's model number but w/o a hit- Not unexpected. Take that amplifier chassis out of the unit (if needed) and look for a number inked on the chassis. It may also be on a sticker, nameplate, whatever. That will give you the model # of your amplifier and that's your search term. Using those #s to search on eBay, I had an old Zenith console stereo amp for which I was able to purchase a repair kit complete with all the parts I needed to rebuild the unit. Sounded sweet when I was done, love them tube amps.

I would imagine there's lots of rebuild kits available on eBay for your model as they made a ton of console stereos w/ identical amplifiers. Good luck!
 
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I_AM_CANADIANOffline
Post subject:   PostPosted: Apr 27, 2014 - 07:32 AM
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stephenjaye wrote:
First off, those two terminals marked "G" and "A" are for an external antenna.

As for the loud hum, there's a 90% chance it's a capacitor gone bad. I searched your console's model number but w/o a hit- Not unexpected. Take that amplifier chassis out of the unit (if needed) and look for a number inked on the chassis. It may also be on a sticker, nameplate, whatever. That will give you the model # of your amplifier and that's your search term. Using those #s to search on eBay, I had an old Zenith console stereo amp for which I was able to purchase a repair kit complete with all the parts I needed to rebuild the unit. Sounded sweet when I was done, love them tube amps.

I would imagine there's lots of rebuild kits available on eBay for your model as they made a ton of console stereos w/ identical amplifiers. Good luck!
Many thanks! I will do that.

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elvisluvsOffline
Post subject:   PostPosted: Apr 27, 2014 - 08:25 AM
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Would anyone know if this type of amplifier has lethal shock potential? Or is it usually older ones? Good luck with your repair-m
 
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Post subject:   PostPosted: Apr 27, 2014 - 10:37 AM
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Stephen hit the nail on the head. Your loud hum is caused by a faulty capacitor, probably in the power supply section. And yes,, elvisluvs, be careful - the power supply caps can hold a shock potential. It's best to arc the 2 cap leads with each other before working on it. This will drain off the charge.
 
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Post subject:   PostPosted: Apr 27, 2014 - 11:34 AM
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Is that model number for the whole console or just the amp? If it's for the whole console I would try to find the the model number of just the amp and search for that. Other consoles may have used that same amp and there may be a Sam's Photofact for it. If you have stores nearby that sell vintage gear they'll usually know someone who works on this stuff. Do you have soldering skills/equipment? The ability to test the tubes would be nice too.
 
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Post subject:   PostPosted: Apr 28, 2014 - 08:47 AM
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Let's talk about the electrical shock potential in that amp. As long as it's disconnected from your home's wall outlet, the most you'll get from one of those electrolytic capacitors is similar to a static spark one can generate during the winter months inside. A small bite but unless one is very, very unlucky it's not going to do you serious harm. The poster who raised this caution is probably thinking of the second anode lead in an old CRT television. The picture tube acts as a big capacitor and can store anywhere from 10,000 to 30,000 volts for quite a long time- That will definitely get your attention and can be lethal.

Notice that when you took off the back to your stereo console you automatically disconnected it from your 110 vac wall receptacle, and so the dangerous B+ voltages that power the tubes aren't present.

Back when we were young and stupid apprentices, we would charge up those large paper caps and leave 'em lying around as a practical joke. Never killed anyone Wink
 
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Post subject:   PostPosted: Apr 28, 2014 - 12:01 PM
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stephenjaye wrote:
Let's talk about the electrical shock potential in that amp. As long as it's disconnected from your home's wall outlet, the most you'll get from one of those electrolytic capacitors is similar to a static spark one can generate during the winter months inside. A small bite but unless one is very, very unlucky it's not going to do you serious harm. The poster who raised this caution is probably thinking of the second anode lead in an old CRT television. The picture tube acts as a big capacitor and can store anywhere from 10,000 to 30,000 volts for quite a long time- That will definitely get your attention and can be lethal.

Notice that when you took off the back to your stereo console you automatically disconnected it from your 110 vac wall receptacle, and so the dangerous B+ voltages that power the tubes aren't present.

Back when we were young and stupid apprentices, we would charge up those large paper caps and leave 'em lying around as a practical joke. Never killed anyone Wink



So are you saying this true with older 50's models as well? I have a couple of 50's models I would like to restore, but i'm scared to touch them Laughing

My RCA model has a loud hum and low volume output
 
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stephenjayeOffline
Post subject:   PostPosted: Apr 28, 2014 - 02:03 PM
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throbbingpuppy wrote:
stephenjaye wrote:
Let's talk about the electrical shock potential in that amp. As long as it's disconnected from your home's wall outlet, the most you'll get from one of those electrolytic capacitors is similar to a static spark one can generate during the winter months inside. A small bite but unless one is very, very unlucky it's not going to do you serious harm. The poster who raised this caution is probably thinking of the second anode lead in an old CRT television. The picture tube acts as a big capacitor and can store anywhere from 10,000 to 30,000 volts for quite a long time- That will definitely get your attention and can be lethal.

Notice that when you took off the back to your stereo console you automatically disconnected it from your 110 vac wall receptacle, and so the dangerous B+ voltages that power the tubes aren't present.

Back when we were young and stupid apprentices, we would charge up those large paper caps and leave 'em lying around as a practical joke. Never killed anyone Wink



So are you saying this true with older 50's models as well? I have a couple of 50's models I would like to restore, but i'm scared to touch them Laughing

My RCA model has a loud hum and low volume output


The voltage stored in those old paper caps bleeds off, probably in the time it takes to get all the screws off the back of that old console. Smile If it would make you feel a bit easier, use an insulated jumper to touch all the leads of the caps you'll usually find underneath the metal amplifier chassis. Clip the other end of the insulated jumper to the metal chassis first, btw.

One great rule of thumb is to keep one hand in your pocket! This way, if you touch something "hot" there's no possibility of the shock running across your chest (and heart) and through the other hand that may be grounded.

Good luck with your restorations.
 
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RidinTheWind
Post subject:   PostPosted: Apr 29, 2014 - 12:01 PM
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I recall reading that it may take a day or two for the charge in a capacitor to bleed off by itself and that the shock from some can be very bad. Best to short the two leads with an insulated screw driver. You will likely hear a loud pop.

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