General Electric RC-4851 coffee table stereo

[nmonj84]

I'm looking for any insights folks might have regarding this model. When plugged in I hear a hum sound. Some of the tubes get warm, others dont. I so far replaced a 12AX7 and a 6AQ5A but that didn't seem to fix it. Before i wonder down the rabbit hole of vintage audio, i thought i'd understand what i'm up against from folks who have done this before. i'm commited a few hundred bucks on replacement tubes thus far. Trying to avoid a project int he living room with 5 and 7 years olds. Some foresight from you all would go a long long ways. A redit forum suggested it was the capacity that was likely bad and to swap that first. A parts diagram woudl be super helpful.
Images attached for reference. The sticker ont he bottom says its RC 4851 B

[TC Chris]

The hum is likely from a defunct filter capacitor, that big tubular orangish thing in the photos.They die. Do not buy new tubes until you know you need them.

The filter capacitors need to be the same (or somewhat greater) values in microfarads (mfd) and voltage rating. This big ones are polar--maintaining polarity (+, -) is crucial.

It's usually wise to replace paper capacitors (usually smaller tubular devices) too. Same voltage/capacitance, with no polarity to worry about. When these get leaky, they let DC get where it's not supposed to be and mess up tube performance. Disc-shaped capacitors are ceramics and usually do not need replacement.

The good news is that these capacitors are cheap. But they require desoldering/soldering, which may take a bit more time.

Chris Campbell

[William]

I see your dog is guarding your GE, or at least attempting too. I like the black trim and the way it highlights the walnut finish. Was it that way when you got it?

Bill

[nmonj84]

Thanks!

Chris
I could use a short gameplan to follow, maybe you could critque my plan :

1) figure out if i can de-couple the two electronics boards under the tuner (shown in images); would be nice if i can work on this seperate from the coffee table and intermittently connect it and test it (might need to install a few quick-connects.
2) purchase a multimeter and de-soldering gun. I own an soldering iron and some decent tin from a recent build with my son(that was my first time soldering though; tin that came was the gun was awful).
3) search replacements for the filter capacitor, if cheap, proactively replace without testing if it was bad. Original markings:

• 112B3518-10
  100 MFD 300 VDC
  75 MFD 300 VDC
  70 MFD 25 VDC
  (bracet obscures potentially 1 cm of text)
  BLK. COM. NEG.
  Oper. Temp. 65C

4) photograph the boards in better detail when they are outside the coffee table; load here and re-group.

William,
In 4Q18 I was given the table from an old mentor of mine at work. He has a knack for cool things but listens to his wife when his horading gets out of control. My wife and I were remodeling the inside of our recently purchased home and she and the contractor decides that the table could use a fresh finish; the trim was their idea and we like it as well! Since then, kids water bottles has left marks; in another year or so, i'll likely refinish it again. certaintly will if i can get it working again.

Last comment/quesiton. Would I ruin this piece if i added in a bluetooth receiver to the speakers while i'm in here? It would be fun for the family to put on any tunes; then again i have a neat seagan radio that can do that for me just fine. I may go quite for a while but will be reading up and working towards this goal. thank you for your insights!!! Chat GPT doesn't quite understand vintage audio.

[William]

So, the first thing I would do is try and find a schematic for your GE, that will help you immensely as you tackle this project. There is lots to do, but all in good time. Baby steps are recommended.

Nick, I highly recommend that you totally read through the post under "OTHER CONSOLES," GE Wellington coffee table stereo by stbasil." He has what you have minus the tuner/radio. You will gain real insight as you read through what he did, and you will basically be doing the same thing to yours as stbasil did to his. Then, please start a new thread under "OTHER CONSOLES," one that pertains to your GE that way it will be easier for us to find you and give you a helping hand. And yes, you should be able to add Bluetooth to your GE, if I remember correctly, stbasil did just that.

One more thing, would you please provide a photo of the control panel so we can see what controls you have. Thank you.

I hope this helps and remember it is all about baby steps.

Bill

[Hi-Fi-Mogul]

NIck,
See if Greg can move your post to create a new
separate topic for your G.E.

It will simplify the process going forward.

[electra225]

This topic has been moved here so we can better help the member with his project. I hope this works like I THINK it should. This is my first attempt at doing this, so bear with me...

I did it! It actually worked out like I'd hoped it would....

Please don't even plug your GE stereo in again until you get those filter caps changed. In any GE device that we would work on here, you can bet the filter caps are going to be severely leaky if you are lucky, and plain shorted if you are not. You can take the power transformer out if they short. That chassis should be the same one used in my Trimline 300, so it will be here on the forum, in Downloads, located in the navbar at the top of this page. When changing the filter caps, I recommend using 100uf at 450 volts for both filter caps, then whatever you have handy with more than 50 working volts DC for the cathode bypass cap. These three capacitors are located in the orange cylinder you have in one of your pictures. I have a supply of 100uf at 100 volts I like using for cathode caps since they aren't much good for anything else. If you need to buy new caps for cathode bypass, use something like at least 70uf, increasing the value from original.

[TC Chris]

Thanks!

Chris
I could use a short gameplan to follow, maybe you could critque my plan :

1) figure out if i can de-couple the two electronics boards under the tuner (shown in images); would be nice if i can work on this seperate from the coffee table and intermittently connect it and test it (might need to install a few quick-connects.
2) purchase a multimeter and de-soldering gun. I own an soldering iron and some decent tin from a recent build with my son(that was my first time soldering though; tin that came was the gun was awful).
3) search replacements for the filter capacitor, if cheap, proactively replace without testing if it was bad. Original markings:

• 112B3518-10
  100 MFD 300 VDC
  75 MFD 300 VDC
  70 MFD 25 VDC
  (bracet obscures potentially 1 cm of text)
  BLK. COM. NEG.
  Oper. Temp. 65C

4) photograph the boards in better detail when they are outside the coffee table; load here and re-group.

William,
In 4Q18 I was given the table from an old mentor of mine at work. He has a knack for cool things but listens to his wife when his horading gets out of control. My wife and I were remodeling the inside of our recently purchased home and she and the contractor decides that the table could use a fresh finish; the trim was their idea and we like it as well! Since then, kids water bottles has left marks; in another year or so, i'll likely refinish it again. certaintly will if i can get it working again.

Last comment/quesiton. Would I ruin this piece if i added in a bluetooth receiver to the speakers while i'm in here? It would be fun for the family to put on any tunes; then again i have a neat seagan radio that can do that for me just fine. I may go quite for a while but will be reading up and working towards this goal. thank you for your insights!!! Chat GPT doesn't quite understand vintage audio.

[TC Chris]

Ack!!!!!!!!!!! I just typed out an extended reply and only the quotation got posted!!! I'm too slow a typist to do it again tonight. Summarize: figure out color codes on that big capacitor (and the other one like it in one of the photos). Match voltage rating or go higher. New standard capacitance values are different than old ones; chose next-higher new standard value.

Chris Campbell

[electra225]

GE didn't believe in using plugs to connect all the components. They hardwired everything. There is no neat way I know of to work on it. You have to come up with a plan that will work, usually different in every case. GE was fairly minimalist in how they built things, but their stuff performed surprisingly well for what it was. GE was good about using a certain chassis in several different models, which makes service information easier to find in many cases. I have an RP-1590 C stereo that I restored, including recovering the cabinet. I took all the components out in one piece. GE built their stuff so you could do that, the secret is to finding out how they intended that to take place. There is instructions in the service literature for that particular stereo, not sure if it is included in others or not. You want to check the grounds on the printed circuit boards. The tone boards can be problematic if they have been mishandled. The tone controls are mounted on a printed circuit board, with the controls mounted in such an orientation that they are hard to clean installed in the cabinet. You have to remove the tone board from the cabinet, then wrestle it around so you can get to the controls to clean them, something that should be done. Be careful as you handle the tone board. If you damage it, it can cause all kinds of hard-to-find issues. It can be hardwired if you break a trace. The hardest part about that is finding the break. I would really recommend that you replace the filter capacitors so it is safe to run, then get a baseline of performance on it before you do anything else. This initial investigation with it running will let you know what issues you have, and you will also know if you have an issue after you worked on it where to look for the issue. GE stuff isn't hard to work on, and will make a good beginning project.

[Hi-Fi-Mogul]

1. Please post the vacuum tube complement for both
the audio amp and radio circuit.

I have 2 possible schematics, but need more info.

2. Take a good look through the "Getting Started" section for
general "must do" tips on vintage restorations.

3. Can you read a circuit schematic ?

It can be a bit challenging, as the real topography of
the amplifier/radio chassis does not equate to the
nice linear layout of a schematic.

4. What is your electonics' knowledge base ?
I'm not sure if I saw anyone ask that.

5. The Garrard Autoslim record changer is a good
unit, and we'll help with that service, also.

[electra225]

Thank you for your kind offer of help with the schematic, Mr. Mogul. In the way of a suggestion, "stbasil" posted the schematic for his stereo in Downloads. That information may be pretty close to what will work with this stereo. My bet would be the difference between the two instruments would be the cabinet style.

[stbasil]

FYI, the schematic I uploaded (from radiomuseum), and the one in the 1964 Beitman's book are only for the amp, which worked for me since my model doesn't have the tuner. And the component designations in the radiomuseum schematic don't agree with the PCB markings in my model, though it's accurate otherwise.