General Electric console stereo guts resurrection

[electra225]

I am "cleaning and tossing" in the shop. I have tossed a lot of books, parts, tubes, speakers things "I know I'll need that someday" stuff. I can't store it, don't want to keep it organized, am tired of looking at it. Nobody wants it, I don't need it, the round file is scoring.

I came across a box with the guts of an old ugly GE stereo. The cabinet was made of "mystery wood" looked like a combination of cardboard and sawdust. It was in poor shape and had a sprayed-on finish. It had a beautiful 1200-series VM changer, with GE's "Custom" tone arm. I removed the guts and changer, put the rest on the burn pile. I would offer this chassis as a little project to help our new member as he starts on his Zenith radio project. I have no idea the condition of this outfit, it is missing all the amp tubes, and I can't find any identifying numbers to tell the model. Maybe some of our members talented at identifying chassis can come up with a model number. This outfit has a full-stereo AM-FM tuner and basically the same amp chassis as the old RP-1590 I restored and have run the wheels off of since. There are seven tubes in the tuner, four in the amp chassis. It has "Magnavox style" wiring, with the external speaker RCA jacks connected with wire nuts. Yep, FACTORY wire nuts, not a hack. Tinkering with this chassis will give our new member an idea how to proceed with confidence on his project and will be better than just tossing these guts with no benefit to anyone. With no cabinet to work with, it will be easier to see everything out in the open. I'll take pictures to clarify the text. What say ye?

[electra225]

I can't get to the shop right now due to the spambot invasion, but I can add some context to this project.

First off, some experience I have had with GE equipment. When you open up a GE device and see the brown paper filter cap, replace it before you plug in the device. It will be bad 99.99999% of the time, shorted usually. These power transformers are not known for being wimpy, but I have seen two or three of them blown because of this filter cap being shorted. Second, GE uses Muntz engineering, but gets lots of performance out of minimal componentry. Their early printed circuit chassis are not the best, and this amp chassis typically tends to suffer from a badly baked printed circuit board. This particular one is in beautiful condition. I'm guessing it has had low hour usage and it is better ventilated in this console cabinet than it would be in a smaller cabinet. This amp chassis uses 7189 single-ended output tubes. You can use 6BQ5's but it drives them pretty hard. The famous/infamous printed circuit tone control board is probably the worst feature of this setup. These boards develop hairline cracks that cause you to exercise your vocabulary, but are elusive to see and repair. Fortunately, hardwiring the entire board will fix it.

This particular setup is trying to be a Concert Grand. You may notice the white plug I took a picture of. That plug supplies power to the tuner chassis, which has its own power supply. It has a selenium rectifier and filter cap. So, the initial power up will necessitate unplugging the tuner pending checking it's power supply for safety. I will perform my safety check on the amp chassis, then power it up after changing the filter caps, including the cathode bypass cap. The filter caps are 100 uf @ 450 volts. I use a 100uf @ 100 volt cathode bypass because I have several of those and they aren't high enough voltage rating for filter caps. My safety check has been poo-poo'd by the radio snoots, but it has served me well and it was how I was taught. On a transformer power supply, you need not less than 500K ohms on the filter caps to ground. Less than that may be considered a short. On transformerless supplies, 50K is my spec. In this case, I'll change the caps just because. Then I'll find out what AC is to the plates of the rectifier. The plates of the rectifier have the highest voltage in the chassis, it is AC. The highest DC is at the cathode of the rectifier, then filtered for use by the chassis. Our first task will be to determine if the transformer is good, has 6 volts for the tube filaments. I'll include pictures to show how I do this....

[electra225]

Our first tests were positive. I had to change my plan a bit. The white power plug on the amp chassis needs to stay there in order to supply power to the amp chassis, via the controls on the tuner, just like Magnavox. I should have known better. I connected the entire outfit to my Kill-A-Watt device. This measures line voltage and wattage used by the chassis. You will see that at 113+ volts line AC, the chassis pulled a tad over 28 watts, this without the rectifier or any high voltage on the chassis. This wattage represented the draw of the tube filaments in the tuner and the dial lights. During the test, I determined that the power transformer is good, witness the 300 volts AC on the rectifier plates at the octal socket and the dial lights and tuner tube filaments glowed. Our next procedure will be to replace the filter capacitors, repopulate the amp tubes, then see if we have B+, the high DC voltage required to power the various circuits in the chassis. At that point, I will need a schematic to proceed further without guessing.....

[electra225]

Guys, the spambots are trying to shut us down.....

Wonder of wonders, this contraption actually works! And, more wonder of wonders, it sounds pretty good! It originally ran 6X9 speakers in the console, but I have it connected to my Fisher 15" stereo speakers. Good bass, not so bright of treble, but that might be correctible with more work. The controls are all dirty, I had a bunch of dirty tube sockets in the tuner chassis. The whole thing pulls a tad over 75 watts in full song. The dial lights all work, the power transformer is cool as a cucumber running about two hours at 120 VAC on the line. I don't keep 100uf @ 450 volt caps on hand, so I employed my "GE kluge" caps, consisting of a two 47uf caps paralleled with a 10uf for one 104uf cap the other is a 33uf and a 47uf paralleled with a 24uf cap for 104 uf for the two filter caps and I used a 100uf @ 160 volt cap for the cathode bypass, since I had that on hand.

I don't know what I'm going to do with this thing now. I have no real use for it, no real interest in it. Somebody need it for parts? It works, not too bad, either. Seems a shame to toss it.

The thing is kinda deluxe for a GE. External speaker jacks, tape input, scratch filter, kind of a fancy tuner bezel. Nice heavy metal knobs and a counter-weighted tuner knob. Plus it has connections for the changer, set up for VM.

[William]

Greg, do you have a photo of the controls/tuner?

Bill

[electra225]

I can take some pictures if you'd like. I am going to solder the connections under the wire nuts. They are just twisted together. How this thing has survived all the years it has and has been in storage and kicked around and those connections are still together and good is a minor miracle. The AM band needs a good alignment. I have it running on a pair of Amperex 6BQ5's and I think I like the sound of those better than the 7189's. I may swap my RP-1590 over to 6BQ5's.

[William]

Thanks, Greg, for posting the photos. I was curious about what the control panel looked like, wanted to see if it resembled the GE that I worked on for the antique guy. Similar by, same theory just a little different.

Bill

[electra225]

The controls and the VM changer were the only two nice things on that nasty old console. It was one of those that are Colonial style that you can put a TV into that cabinet, then run the audio thru the tape input on the tuner. I found the original 6X9's it had when it was in one piece. I put these guts back upstairs. I can't toss something that basically works and that someone may get some good out of.

[William]

Good plan and hopefully someone will want them

Bill