Magnavox Model 2ST643

[jheroux]

I have a Magnavox model 2ST643 with the 8803-00 Amp. I just had the turntable serviced and it's functioning wonderfully, but I am getting a distorted sound coming out of the speakers whether it's on the radio or phono etc. Sure would like to get it fixed up and sounding good.

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[electra225]

Welcome aboard! I'm glad you found our group. I hope you will enjoy yourself and will post often....

I have a Magnavox model 2ST653, which is basically the same instrument as yours, just a different cabinet style. I have been playing it today listening to some Lawrence Welk CD's. I find mine to be a competent performer. These would be 1963 model year instruments. The only downside I see to these models is that they don't use the proprietary Magnavox Multiplex adapters, you have to use aftermarket, stand-alone adapters.

Distortion can come from almost any component in the chassis. You could have a weak tube, a weak rectifier, a bad speaker, a loose speaker, almost anything. If the distortion appears in all modes, as you have suggested, then it is reasonable to place suspicion on some component in the audio amplifier system. Your stereo uses the dratted 6EU7 audio tubes, known to be problematic. I believe I would start my gaining a bit more information before suggesting a path of troubleshooting. It is highly recommended you find a schematic for your stereo. There should be one in Downloads, in the navbar at the top of this page, under the header. Is the distortion in both channels? Is it worse on bass notes? Does the high end, the treble, sound clean?

What electronics experience have you had? Can you solder? Can you read a schematic? What electronic repair tools and equipment do you have? This information will help us help you come up with a plan of attack.....

Another observation on these little Magnavox stereo consoles. My 2ST653 has the bad habit of vibrating its speakers loose. The boards the speakers are mounted on are not well-secured to the cabinet. The speaker boards come loose and rattle against the cabinet on occasion. This rattling noise sounds much like a speaker with a loose cone. I finally got mine to pretty much stop doing this, but the methods I used are varied and not always very pretty. You might try turning the treble to maximum and the bass to minimum and see if the distortion goes away or changes. This might give a clue as to whether the distortion is internal to the chassis or external, such as speakers and/or their mounting.

[jheroux]

Thanks for the quick response! I'll have to check sound again tomorrow, I know for sure it is both channels and I think it's also both treble and bass. I have some experience in electronics, I can read a schematic and I can solder but other than a multimeter I don't have any real troubleshooting tools.

[electra225]

Did you read my comment about your posting your location in your user profile? Thanks for taking care of that.....

The comment I made about treble and bass was this. If you turn the treble full on to maximum and the bass at full minimum, you should be able to change the distortion if it is generated in the speakers. If the distortion is generated in the chassis, this may not make much, if any, difference. Turning the bass down will show speakers that have defects or mountings that may not be tight. Grid emissions in output tubes is a common cause of distortion, although the 6V6's used in that amp aren't prone to having grid emissions. Probably in order to troubleshoot the two chassis in your stereo, you will need to remove the electronics from the cabinet and connect them on your workbench so you can take voltage measurements. It would be nice to have a tube tester, or at least have access to one. The 6EU7's are spendy, but the other tubes aren't all that bad, pricewise. That chassis will require having all the coupling capacitors and filter capacitors in the power supply changed. Then you'll need to take voltage and resistance readings to further troubleshoot.

[William]

Does your unit have a speaker switch? Make sure that all of your controls, Loudness, Bass, Treble, Function, balance if there is one hidden, and speaker if there is one, controls are clean. Also during your restoration be sure to add a fuse to your amp chassis. The fuse will help prevent a failure that might take out components especially the power transformer. I know this is a lot to take in, but it can all be done in baby steps so you can learn as you go. The important thing is to have fun as you take this journey.

Bill

[jheroux]

It does have a speaker switch and it is clearly dirty (as are volume, treble etc ) controls so I have ordered a can of DeoxIT contact cleaner.

[jheroux]

Interestingly enough when I got this console a few years ago the turn table wasn't functioning and I don't recall what else. I put it up for sale on FB Market place and a guy came to buy it. I asked what he was going to do with it out of curiosity and he said he enjoyed fixing them. So instead of selling it, he fixed it for me. I believe he is on this forum!

[electra225]

Do you know what all was done to it? Recapped? New tubes? I realize I am sitting in front of a computer in Arizona and the "patient" is in Michigan, so there is that. All we/I can do is to go from experience to make suggestions on places to start. Since your concern is with both channels, the 6EU7 tube in the tuner chassis would be a strong suspect. I didn't consider the function switch, since my experience tells me that typically only one channel would be affected, or one mode affected, by a dirty function switch. The 6EU7 is a dual triode that serves as an audio amp, one channel for each triode section. If it was weak, or if it had a too-positive grid or a too-negative cathode, that could cause distortion. I would think the external speaker switch might be a suspect, but those aren't moved much and really don't cause a lot of trouble.

[jheroux]

Do you know what all was done to it? Recapped? New tubes? I realize I am sitting in front of a computer in Arizona and the "patient" is in Michigan, so there is that. All we/I can do is to go from experience to make suggestions on places to start. Since your concern is with both channels, the 6EU7 tube in the tuner chassis would be a strong suspect. I didn't consider the function switch, since my experience tells me that typically only one channel would be affected, or one mode affected, by a dirty function switch. The 6EU7 is a dual triode that serves as an audio amp, one channel for each triode section. If it was weak, or if it had a too-positive grid or a too-negative cathode, that could cause distortion. I would think the external speaker switch might be a suspect, but those aren't moved much and really don't cause a lot of trouble.

I don't recall what all was done, but it was simple, I don't think any caps or tubes were involved. you may be on to something also. I played a record for a bit this morning and it didn't sound as bad as the radio does. I can make a couple cables and bypass that speaker switch as a test, but again, I thought the record sounded decent this morning. I'll have to spend some more time with it. But I'm working this weekend so it will be a minute before I can get to it

[electra225]

I don't believe it will be necessary to bypass the speaker switch at this point. Manipulate the switch several times, then see if there is a change. If the record player sounds okay, but the radio sounds distorted, then we may be back to suspecting the function switch. If there has been no capacitors changed, and if the chassis hasn't been completely restored electronically, you could still have issues there. If you have a tape deck or something you can feed into the tape input, see how the stereo sounds in Tape or Aux mode. If it sounds okay there and the record player sounds okay, then we need to look into the radio chassis after the function switch has been cleared of suspicion. Keep in mind, also, that the loop antenna used in that radio chassis for AM reception is EXTREMELY directional. The factory FM antenna is only adequate. If you want better radio reception, you may need an external antenna. There are connections on the back of the cabinet for antenna connections.

[jheroux]

I don't believe it will be necessary to bypass the speaker switch at this point. Manipulate the switch several times, then see if there is a change. If the record player sounds okay, but the radio sounds distorted, then we may be back to suspecting the function switch. If there has been no capacitors changed, and if the chassis hasn't been completely restored electronically, you could still have issues there. If you have a tape deck or something you can feed into the tape input, see how the stereo sounds in Tape or Aux mode. If it sounds okay there and the record player sounds okay, then we need to look into the radio chassis after the function switch has been cleared of suspicion. Keep in mind, also, that the loop antenna used in that radio chassis for AM reception is EXTREMELY directional. The factory FM antenna is only adequate. If you want better radio reception, you may need an external antenna. There are connections on the back of the cabinet for antenna connections.

Just got into it enough to add an rca cable to the tape inputs. I have a blue tooth device I am going to connect now and take a listen!

[jheroux]

I don't believe it will be necessary to bypass the speaker switch at this point. Manipulate the switch several times, then see if there is a change. If the record player sounds okay, but the radio sounds distorted, then we may be back to suspecting the function switch. If there has been no capacitors changed, and if the chassis hasn't been completely restored electronically, you could still have issues there. If you have a tape deck or something you can feed into the tape input, see how the stereo sounds in Tape or Aux mode. If it sounds okay there and the record player sounds okay, then we need to look into the radio chassis after the function switch has been cleared of suspicion. Keep in mind, also, that the loop antenna used in that radio chassis for AM reception is EXTREMELY directional. The factory FM antenna is only adequate. If you want better radio reception, you may need an external antenna. There are connections on the back of the cabinet for antenna connections.

Just got into it enough to add an rca cable to the tape inputs. I have a blue tooth device I am going to connect now and take a listen!

Bluetooth sounded FANTASTIC....little bit excited about that!