1960 Magnavox Concert Grand model 1ST800F rehabilitation

[electra225]

After I get a few smaller projects cleaned up and off my bench, I had decided my next project is a part by part rehabilitation of my Concert Grand. The same procedure as I did on the Imperial, complete with buying four quads of 6V6S JJ output tubes. I will maintain the same tight 5% tolerances on component values. I will match components channel to channel. It will either be easier or tougher to do this with the dual monoblock amplifiers in the CG. The eye tube is comatose. The sound is like the typical "300 pound clock radio" audio response so often criticized in a Magnavox split-frequency, bi-amp, stereo. If I can make as much difference in the CG as I did in the Imperial, this thing will be truly Magnificent......

Stand by for as complete of a text as I can manage, with pictures. I don't know of a similar effort anywhere on the Internet. This should be interesting and may answer some of the questions commonly posed about these instruments.

The first procedure in this project will be to go thru the changer. I know the motor is seized. I want to be able to set the entire electronics up on the bench and get everything adjusted and verified for proper operation before the electronics go back into the cabinet. Not doing that with the Imperial changer was big mistake, cost a lot of unnecessary extra work.

[electra225]

Okay, per our little poll we did on Chat, this is the project that created the most interest. I'll continue on with this topic, since it is not all that old. I have some re-arranging to do in the shop before I get started, so stand by...

[electra225]

Doug mentioned in the topic in Chat something about the speakers, and could they be a part of the strangled bass. Certainly possible. I have been griping/researching/reading about anemic bass response in these things since I got mine in 2014. There have been lots of gassing and blowing, but nothing that I know of that works, and nobody has taken the time to figure it out. The Concert Grand models use two front-firing 15" woofers with different weight magnets. IIRC, one is 35 ounces, the other over 50, but it's been awhile and those might be wrong. Suffice it to say they are different weights, and by a considerable amount. I'd like to do all this in an orderly way so everybody can follow along and so we can all learn something. When I redid the Imperial, I did some research on cathode biasing in the pre-amp section and how that affects bass response. I found that Magnavox used cathode biasing that pretty much bled off frequencies under 1khz and ran them to ground. That did nothing for robust bass response. I tinkered, changed some component values and got bass response better. I'd like to maybe do something a bit more exact and more successful with this project. This thing has two amplifiers to go thru versus the single amp in the Imperial.

[Doug]

I did see the amplifier part in the posted 1st800f download.
can u hook up a different speaker in a cabinet see if the bass is there?
Good Morning
Doug

[William]

Another suggestion, Doug, would be for you to take a look, again in downloads, under the topic of Literature/Brochures which is the last thing listed in in downloads. I have found that very helpful for model number identification and specifications on each of the different models Magnavox built over the years.

Bill

[Doug]

I did not see the amplifier schematic in the download

I left out the not.
Anyway thanks ill read up on the info on the sales literature

[electra225]

The speakers are in allegedly sealed enclosures. Considerable disassembly is required to access them. That will be a part of the investigation as we continue with the project.

[electra225]

To refresh everybody's memory, I took some pictures before I start work. Sharp eyes may notice the cabinet back is not the original. I made that one from a sheet of lauan and wire mesh. I "slathered it in poly" which may annoy the radio snoots who hate such material. This particular back cost about $30 when I did it in 2014. Now, it will cost about $100 for the same project on the Imperial and on the Stereo Theater, both of which I have patterns made for. A 4X8 sheet of lauan is now almost $55. The dust is not too bad for 10 years accumulation. Don't tell my frau, but I found a dead scorpion between the back and the cabinet. The silver thing sitting on top of the tuner rectifier chassis is the bottom of the Multiplex adapter. PB Blaster did an admirable job of keeping the cad dust down on the chassis. I managed to manipulate the Magnavox wiring mess fairly well. I took pictures so I could document how that is routed. The speakers set in front of the amp chassis. I made the lauan back for the cabinet so it would ventilate better and so I could see all those sparkly, clear top tubes as they ran. The Sylvania-sourced 6V6 output tubes are coded the 43rd week, October 21 -27, 1959. You'll see the date code on the tuner power supply chassis is for the 44th week of 1959. That would make this stereo an early 1960 model, since the new models were introduced around Christmas time. Magnavox sold their instruments primarily in furniture stores....

Also for clarification, I did a fairly major tune-up on this thing when I rescued it from a haunted house in Fort Worth in 2014. Filter caps and paper coupling caps, mainly. The tuner dial string had also gotten derailed and had to be put back right.

[TC Chris]

No complaints about your new back from this quarter. It was done in aid of function, as I recall: keep critters and people out but let air flow through. And it's on the back, where in normal use nobody can see it. Ventilation is crucial to longevity in tube equipment. The manufacturers didn't worry much because they designed these devices for a shorter service life than our antiques are enjoying.

Chris Campbell

[electra225]

I have owned this stereo since 2014. I did something this afternoon that I had been waiting for since that time. I played a record on the Concert Grand's old, tired, neglected Collaro Conquest changer.

When I did the tuneup on this thing in 2014, according to my notes, I replaced the drive tire, motor mounts and needle. OF course, I didn't do anything to the motor, nor does my notes indicate that I did. I found the motor seized tight. I used the straw on my PB Blaster can to squirt some penetrant at least in the general direction of the upper bearing last week, then let it set until this afternoon. When I powered up this afternoon, the amp came on, but the platter just sat there. I pulled the platter and found that the motor would turn, but just barely. The changer was in "reject" so the motor had to pull not only the platter, but it also had to pull the cycling wheel, something it was not happy doing. I gave the fan on the motor shaft a couple of helpful spins, and the motor ran at a more reasonable speed. I put the platter back on after it completed the cycle. The motor would turn the platter. I put the Concert Grand demonstration record on. The platter may have been turning, but it wasn't anywhere NEAR the correct speed. Lots of "wow". The music sounded rather bizarre. If I shifted to 45 then back to 33, the speed was better, then it would start dragging again. After it ran for about ten minutes, the speed seemed to be okay. I may have gotten PB Blaster somewhere it shouldn't be. At least I know that the motor is good, the cartridge plays on both channels. The treble is nice and bright, midrange quite clear and clean. Heavy bass notes sound fuzzy at times. Cartridge suspension? It has the brush on the tone arm which are usually hard and hold the needle up off the record, so it probably should be retired. I'll get the changer out of the cabinet and up on the bench where I can tinker with it better. At least I know I have a live patient and can go from there....

[William]

Look at all of those tubes glowing in the dark. Good news that the motor is still good. I pulled the motor apart, which is the only thing I was not afraid of doing to a Collaro changer, and cleaned and lubed it back it on the Symphony. Of course neither the Symphony or the Imperial worked correctly until I read the Magnavox/Collaro service manual and discovered the "E" clip needed to be in place in order for it to reject correctly. This is on Collaro 600 changers, not sure about a Conquest.

Bill

[electra225]

This changer is missing some of the clips that hold it to the motor board, I think. When I turn the bolts that hold the changer down, nothing happens. The clip is gone that holds down the platter, has been since I got it. I'll replace it when I get to that part. The motor probably should come apart. I don't think that the "PB Blaster rebuild" is best practice......

I wonder why the 12AX7 in that right hand amp is so bright?

[TC Chris]

I wonder why the 12AX7 in that right hand amp is so bright?

Same manufacturer and internal structure? Remember the "If it ain't broke" rule. Stick to things that need fixing and leave the some-day items for some other day.

Chris Campbell

[electra225]

I'm not necessarily worried about it. I noticed it and thought it looked odd. I hadn't noticed it before. I have no idea as to the brand of tube it is.

[electra225]

The task for today is to do a bit more tinkering with the changer before it comes out of the cabinet so I can get to the tuner. I need to check tone arm weight. I need to troubleshoot the dust brush to make sure it has not become stiff, so as to interfere with the cartridge tracking in some manner. The needle is a Phfanstiehl, so it has likely been replaced since I've had the stereo. Just as an aside, for future reference, I have noticed that bass response when using the phono input is markedly stronger than when using the tuner or tape inputs. I'm not sure, at this point, that the CG is a "better" record player than the Imperial. It hasn't had all the TLC the Imperial has received so there is that. Maybe I need to do a bit of tinkering to find out what would happen if I fed the tape input and the tuner input to the 12AX7 used with the cartridge. Is the tuner and tape input at a higher voltage than that from the cartridge? Would the tuner and tape inputs overdrive the phono circuit? I have also noticed that the volume needs to be run higher on phono than it does with tuner or tape inputs. Could the old EV 26 cartridge be getting lazy? The cartridge in the Imperial is one of those "Moto Denshi" (I can't remember the right name ) replacements from VM Enthusiasts, but its output is closer to the tape and tuner. And, as another aside, I hope to get enough weight out of the cabinet so I can turn it up on one end and do something so the casters will work. All I had to do with the Imperials casters was to lube them up really well.

And, as yet ANOTHER aside, I hope I didn't plow the dickens out of my Patsy Cline record playing it on a changer that I didn't know anything about.....

[electra225]

YIKES!!! 12.2 grams tonearm weight. Wonder why it didn't sound very good. What an idiot.....

The dust brush seems to be fine at this point.

[electra225]

I got the tone arm weight down to 4.2 grams. It sounded terrible there, so I took it up to 6.4 grams. It sounded better, but still not very good. I used a test record I really don't care about. Putting a penny on the tone arm made it sound pretty good. I need a new needle, no doubt now. I have no explanation why an allegedly new needle sounds so bad. Bad new needle, damage during installation, damage when I moved, who knows. I was afraid the cartridge was bad, and it may be. It's worth risking a new needle to find out. The Collaro manual for the changer specifies 5 grams +/- one gram.

The changer drops records, and shuts off after the last one has played. The "manual play" feature works. The platter doesn't stall during cycling. I think I have a live patient here. I believe "the touch", the normal maintenance is all that will be required. The hard part has already been done.

[William]

Did you pull the motor and overhaul it ? Sounds like it is functioning either way.

Something I found while I was messing with my Collaro 600 from the Imperial. My Imperial has the EV26 cartridge and it does have a new needle. What I found, was when I hotwired my GE/VM changer into the Imperial while I was working on the Collaro 600 my Imperial came alive with cleaner highs. The GE/VM changer has a GE100 cartridge. I wonder if the EV26 is getting weak, or is it the nature of the beast to not produce highs like the GE100 does. They both seem to be the same for bass.

Bill

[electra225]

I've got good highs, no complaints there. The issue with this now is that when it hits a heavy bass note, as in Patsy Cline's double-beat bass, it gets fuzzy, muddy. This and the fact that a penny improves matters, makes me think the needle is bad. Neither the EV 26 nor the GE C-100 is available from Gary. It will have to be really bad before I replace that EV 26. That is my favorite ceramic cartridge. The C-100 runs a close second.

[Doug]

I think your issue is the cartridge is picking up the vibration from the cabinet .
You need to relocate the turntable so it's not on the cabinet see if that's the issue.
Idea have on the back of the cabinet where the wiring may be long enough.
Maybe if your steady enough hold the turntable up with your hands.


In your download of the schematic the audio output schematic is not there.

Have a good day
Doug