Repair of 1961 Magnavox 1ST616 stereo console

[William]

For the crossover capacitors you are dealing with, the 16uf capacitors cut off is 1200 HZ and 33uf capacitors cut off is 600 HZ.

Bill

[electra225]

Perhaps a bit of progress this morning...

I removed the crossover cap on Channel 1. I verified that I have them wired right. I am using two 33uf @ 50 volt electrolytics with the negatives connected, which provides a 16.5 uf non-polarized capacitor. I left the original capacitor, which is larger than the new ones, in place, unwired, to have something to wire tie the new, smaller caps to secure them.

While I am tinkering, I took the liberty of securing the wiring mess a bit better. Nothing is suspended by wires. I used plastic wiring loom loops to hold the wiring up. There was a plastic loop on the tuner that was broken. The orange, green, and black wires for the speakers are too short to suspend from the record compartment like the big one to the amp is. I reckon it will just have to dangle. I thought about lengthening the wires, but that would give me a splice that might look worse.

While I had the crossover cap removed from Channel 1, I cleaned the terminals before I put it back. Now I have a working set of small speakers! The lower one is actually a 5", the upper one is a 4". My next step, then, will be to remove all the connections on speakers, on the amp, on the big speakers, and on both small speakers on both channels and clean them really well. Can it be that there is enough "corrosion" on the speaker terminals that it creates a high-resistance connection and makes the speakers work "wonky"? We'll see.....

You may notice a white plug and a black wire by the amp. Those go to the changer. There were two wires, one green, one black, that ran from the cartridge to the tuner. Moving these two wires would "vary" the rumble and hum in the changer. I replaced those two individual wires with the black, 4' long patch cord. The white plug is for the changer power.

Magnavox used round speakers for the midrange and tweeters. All I have for replacements would be pincushion framed speakers. Re-engineering will be required to mount the pincushion speakers. I really don't believe the original speakers are bad. I decided my best course of action would be to try to figure out why this thing has weak tweeter output, fix it, then leave it like Magnavox designed it. They know a LOT more about stereo design than I do.

[TC Chris]

I have a pair of magnavox tweets, one good and one dead, 580038-1 675829. If the good one would match, I'll send it along to you.

Chris Campbell

[electra225]

I appreciate your kind offer, Chris. Let me do a bit more tinkering to make sure I know what condition these speakers are in before you go to that trouble.

[electra225]

I have been playing some of my cassette tapes while I work with this stereo. I was at an auction in Missouri in 2007. I bought a collection of cassettes big enough to fill the back of our Tahoe, probably close to 500 tapes. Mostly old country music. Somebody did a nice job recording them. I have been enjoying them, testing out this stereo. I am using a Technics dual deck. One side needs a new belt. I have a Sony dual deck that needs both belts. I believe this thing is as good as it's going to get. I'll finish the changer then move on. Along with cleaning all the controls, I also recommend cleaning all the speaker connections.

[electra225]

Here I am, back again....

I managed to monkey with this stereo enough so that I could listen to the front side. At lower volume, I would essentially lose the small speakers on the right side of the cabinet. Turn the volume up, the speakers would come back in, but really didn't still sound right. I removed the bottom speaker on that side and found something I hadn't encountered before. The speaker works, but it sounds really tinny and totally quits at low volume. The pole piece appears to be frozen solid. When I push in on the cone, it won't move. I think this is why it would sound good at times, not so good at other times. I have a speaker I can sub for test. The small speakers on the other channel appear to work okay. I don't believe I have ever run across a frozen speaker cone before.

[TC Chris]

The cone-type tweeters have very stiff suspensions and very little cone motion, even when manually pushed.

Chris Campbell

[electra225]

The other three aren't like that. You can move the cones on all of them. I want to check the resistance on the voice coil on the speaker with the stiff cone. I had to get supper ready which interrupted my testing....

[electra225]

I have a set of nice pincushion-frame speakers that were in set I had one time with nasty cabinets. I replaced the speaker in question with this one. This has restored the audio quality to the channel. Now, what did I find out and what did I learn?

What I learned was that, when the original speaker was in circuit, it essentially shorted the audio to ground. At higher volume, really higher than one could comfortably listen, the signal would pass intermittently. Apparently, the pole piece is dragging on the voice coil. I have never ran across a condition like that, and would probably never have figured out what was going on had I not been listening closely to that specific speaker. I don't know whether I should replace the other mating speaker or not, so that both channels sound the same. The audio is somewhat brighter than before, but I still need to run the control fully advanced. I need to experiment with the value of crossover caps. If I had my way, I'd just wire them full-range and do away with the crossover. I like how it sounds that way, but I don't know if the original speakers that are left will handle that kind of volume.

[TC Chris]

Seems to me that you want to keep a series cap in place so as not to burn up the tweeters. You can probably find some fancier crossover networks online (Parts Express?) that may let you do some sound shaping.

I have a device that came with a speaker that would operate fine for about 5 min.and then lose audio output. I tried to figure out what electronic component was going intermittent, with no luck. Then I plugged a remote speaker into the headphone jack and had audio. Unplug, no audio. Turns out the speaker was the intermittent device. I found a suitable Radio Shack replacement. This is the old RDF I keep on the local sailboat for its FM band. The remote speaker sits in the cockpit and is in use 99% of the time.

Chris Campbell

[electra225]

I have some photos of my speaker kluge, which is working pretty well. I've decided to replace the other lower speaker so they will both be the same. I found a wiring harness from an MPX, so I'm going to splice those remaining dangling wires and run them in a more organized manner. As it is now, the speaker wires are all suspended by the external speaker switch, which seems like poor workmanship to me. I have been playing the collection of cassette tapes I got at an auction in Missouri in 2007. Somebody went to a lot of effort making this collection of tapes. They are not all numbered in order, no idea why there would be missing numbers. I have several dozen of these. All neatly typed. Fairly good fidelity for the most part. No noise reduction, there are a few skips. The only gripe I would have is that they put instrumentals on the end of the tape, between the last full song and the end of the tape. I would prefer the dead tape. They also used TDK tape, the brand Walmart sold. Typically not very good tape, this stuff has weathered the years well. Most were recorded in the 1991 to 1995 era. The person who had the sale was a lady who had gone to a nursing home. Somebody had a huge record collection to share. The songs are all by different artists. 99% country music.

[electra225]

I've been procrastinating on ordering parts. I finally got that done. Drive tire and needle are on their way. I have the midrange speakers changed, have the rats nest of wiring somewhat, actually considerably, neater. The two wires on the front of the cabinet are the input wires from the tuner to the amp. The two light-colored wires on the right hand side hanging down are the external speaker wires. I'll put the service literature I have in a manilla envelope and leave it in the cabinet. We'll get the changer sorted after the parts come and we'll see what we have.

[William]

Very neat and well organized. It is too bad that Magnavox did not take the time when it was built.

Bill

[electra225]

I put about a foot of wire in the orange, brown, and black wires going to the right hand speakers. That is all the extra wire needed to be able to run those wires so they don't dangle on hot tubes. This stereo has the only factory authorized installation of the Multiplex adapter so it isn't in the hottest part of the cabinet. I used white wire ties to separate the wires by component and so they would be better supported.

[stacash]

Sounds like a classic power-switch issue through the function selector. On many Magnavox consoles the “Phono” position routes power through the changer switch, so if that leaf switch or its wiring opens up, the amp goes dead only on Phono. Testing the tuner/amp live on the bench without disconnecting anything is a good approach. Once you’ve got it accessible, check continuity through the phono power circuit and the changer switch. Looking forward to the pictures — they’ll help pinpoint it.

[electra225]

Thank you for your input, stacash. We would invite you to complete your registration by posting your location in your user profile. Everybody makes this mistake, it seems, so you're not alone. We welcome you to the forum, and also ask that you review the rules so as to prevent any misunderstanding. Your first three posts must be moderator approved, per the rules. You will need to post your location for your second post then post an avatar for your third. Please refer to the pictures in this topic, which may confirm that your recommended diagnostic procedures were followed. I'm waiting on parts for the changer, get that sorted, and I'll be done with this project. Again, welcome aboard!

[stacash]

These rules are a bit confusing

[electra225]

Sorry for the confusion. I see you have posted your location and have posted an avatar. Thank you for that. I will be happy to do what I can to clear up any confusion. What is your concern?

[stacash]

I worded things poorly — I hadn’t read the forum rules carefully. Sorry about that.

[electra225]

No problem at all. That's what I'm here for, to help whenever I can. Again, welcome to the forum. I hope you will enjoy spending some time with the best group of audio/console stereo enthusiasts on the planet. This is a friendly and helpful forum and we hope you will join us and post often.