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Restoration of a Magnavox Concert Grand model 1ST800F

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Post by Wildcat445 on Fri Jun 26, 2015 12:57 am

Crossing our fingers is appropriate. It will be a long time before the smile however. Lots of work still to do.

WC

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Post by neali on Fri Jun 26, 2015 2:00 am

You drive me crazy.

Back in the day, when you were winning best in show, did you wait for that seventh coat of clear coat to dry before you tried to see if the engine turned over?

You have TWO restored Amps. Play some music.

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Post by Wildcat445 on Fri Jun 26, 2015 12:56 pm

Patience, patience.  Very Happy

You are almost more excited than I am.  Firing this thing up in one piece is always scary.  Like the first start of a freshly rebuilt engine.  I would frequently let one sit for about a week after I got it ready to start.  A tradition of procrastination, perhaps?  Rolling Eyes

I believe the first song I will play is "A Way To Survive" by Ray Price from his "Touch My Heart" album from 1967.  It has a unique triple bass part and a guitar riff by Willie Nelson.  And, I have it on CD and the CD is in the CD player, which is sitting on top of the CG cabinet.  

How's about some pictures first?  It is raining and I don't want to walk out to the shop to get my tools in the rain.

RCA had Nipper the dog.  I have Percy the pesky cat.  My almost constant electronic companion.  This is the Channel 1 amp fresh from the cabinet.
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Filter cap in the Channel 2 amp that had spewed its guts.  I have never seen a Mallory cap that was leaky like this.  I was really lucky that I did not fry something important in the little time I actually ran this instrument.
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Channel 1 amp done and ready to go back into its cabinet.  These amps are a pain to install laying on the floor with arthritis in my wrists.  I added a fuse (lower right hand corner) and filter caps on terminal strips (upper right hand corner).
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Chassis code.  "1-49-9".  Run 1, week 49, 1959.  This code verifies that I have what would be considered a 1960 instrument rather than 1959.
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Channel 1 amp done, topside.  I did not polish anything except the old filter cap cans and the covers for the tone chokes.  I cleaned the chassis with lacquer thinner and acetone and put exactly three drops of PB Blaster spread really thin on the chassis with a paper towel.  I was going to use WD-40 but had the PB Blaster suggestion.  It worked out pretty well.  I use this stuff to hopefully prevent that white buildup from the cad plating.  I used to use this on car hood hinges to keep them from turning white.  
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Channel 2 amp back in the cabinet. Wiring lead dress will be addressed later.
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And last, but not least, and since this is my thread, here is something I found for Neali.  I know you had a '69 Wildcat, and here is a pic of a buddy's '68 I took when he stopped here on his way to the Buick National Meet.
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WC

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Post by Wildcat445 on Fri Jun 26, 2015 2:38 pm

The Concert Grand has been running for awhile now. Everything is okay, with the exception of a really dirty tuning cap in the radio. Amp draw is just shy of 4 amps. The MPX adapter and Phantom Control chassis will add to this, but I should still be well shy of 5 amps total. The power transformers run really cool to this point, possibly due to them being further from the rectifiers than is sometimes found. I'm not making any assessment of performance yet, since I have to go thru the radio chassis to check the pre-amp circuits. The hum is totally gone. Just a little hiss from the treble amps, but that is about it. I have the treble amps turned up about a quarter of the way. I have to run the volume control more advanced than before, but that was my goal. To make the bass amps work harder. So far, so good. I figure if it has run for 5 minutes without anything going wrong, it will run for another 50 years. The radio chassis and power supply is next. IF the frau will let me turn it off. I think she likes it, finally.

WC

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Post by jerryhawthorne on Fri Jun 26, 2015 4:21 pm

Very Happy Very Happy  WC, now we are talking.  Keep us posted and the frau being happy is the best thing that could happen, well other than all of us being happy.
Best,  Jerry

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Post by Wildcat445 on Fri Jun 26, 2015 4:32 pm

The audio quality typically would start to deteriorate more and more as the instrument ran and everything got warm.  That seems to have been eliminated.  Again, I'm not going to offer an assessment of performance just yet.  It ran for a longer stretch this morning than it has since I've owned it.

WC

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Post by 75X11 on Fri Jun 26, 2015 5:26 pm

That's great news!
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Post by Wildcat445 on Sat Jun 27, 2015 6:30 pm

I have removed the tuner and power supply chassis from the cabinet.

To remove the tuner and power supply chassis from the cabinet you must:

*Remove the cabinet back panel from the cabinet.
*In the record changer compartment, first remove the 45 rpm adapter from its holder.
*Remove the 45 rpm adapter holder from the cabinet, removing two Phillips head screws. (This may not be found on all models. Some models had the 45 rpm adapter in a well in the corner of the changer itself.)
*Working from the rear, unplug the power plug to the record player motor, the Phantom Control plug, and both wires from the cartridge to the amplifier. Then position or remove the clips that hold the changer into the cabinet. Position the speed selector in the "16" position. Remove the changer by lifting straight up, wiggling as necessary to clear any obstructions.
*Remove the control knobs from the front of the tuner.
*Next, unplug the amplifiers from the power supply chassis. Unplug the speaker cable from the tuner chassis. Unplug both input cables from the amplifiers. Unplug the Phantom Control cable from the tuner chassis. Secure any other cables, such as for the tape deck, etc., along with the power cord for the tuner assembly. On each side is a wooden wedge that holds the assembly into the cabinet. Remove the forward-most bolts first. This will release the wedges. You may need to wiggle these wedges to get them to come loose. Remove the rear bolts. Remove the bolt holding the external speaker connections. Then just gently pull rearward on the board under the two components and remove the assembly from the cabinet.

The tuner and power supply chassis are mounted on a 1/4" tempered Masonite panel, painted satin black. On both sides and all the edges. This panel sits on a purpose-built compartment made of what appears to be ash hardwood, stained like the outside of the cabinet, just not finished and hand rubbed. There is a goober in the black paint on the Masonite panel, so I may respray it before I stick it back in.

WC

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Post by Wildcat445 on Tue Jun 30, 2015 12:14 pm

This may be a tad precipitous, but the pre-amp circuit in this instrument contains a cathode follower.  I did not feel that I understand all I know about a cathode follower circuit, and this link is the best explanation of cathode followers that I have run across.  Hopefully, it will prove ample when the time comes to discuss the cathode follower circuit.  

http://www.tubecad.com/2011/08/blog0212.htm

A cathode follower is used to match a high impedance signal to a low impedance load.

WC

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Post by 75X11 on Tue Jun 30, 2015 2:40 pm

Nice work, so far.
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Post by Wildcat445 on Tue Jun 30, 2015 4:26 pm

Thank you, 75. Very Happy

WC


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Post by Conelrad on Wed Jul 01, 2015 4:06 am

I think this is a stellar job of saving a real classic!

cheers cheers cheers

DG

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Post by Wildcat445 on Wed Jul 01, 2015 1:29 pm

Thank you, Dennis. Very Happy

WC

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Post by Wildcat445 on Wed Jul 01, 2015 4:30 pm

I had some bench time with the tuner today, since it is too wet to do anything else around here.  There are not a lot of discreet components under the chassis.  Most everything is in couplets.  On one hand that is good, in that it keeps the underside neat.  The other side of the coin is that couplets limit modifications for enhanced performance.  Most of the discreet caps are ceramic, so those did not get changed.  There is a cathode by-pass cap for the 12AX7 pre-amp and a .47uf coupling cap that I changed.  There is an e-cap in the tuner strip, PCB mounted that I also changed.  It is under the shield on top of the PCB.  I changed a couple 220K ohm resistors in the audio section, since these are known to drift high. The 6E5 eye tube was dead. Graveyard dead. Even checked to have an open filament. I replaced it with a new RCA. The original was RCA supplied, date coded "274-4359".  Everything else checked out.  I am going to replace all three 12AX7's in the tuner with JJ's.  The one that serves as a cathode follower checks intermittently shorted when it gets really hot.  One of the others is weaker when warm than when cold.  Out they go.  I cleaned all the switches and pots.  I am doing some cosmetic cleaning while I wait for parts.  I will have to re-stuff the filter cap can on the tuner chassis.  It contains three 30Uf @450 volt filter caps.  There is no room under the chassis to mount a terminal strip to hold e-caps that is far enough away from the front end of the radio for my comfort.  I installed a larger power cord in the power supply chassis.  Magnavox uses the same size power cord on a clock radio as on this Concert Grand.  I replaced the power cord with a #16, which certainly LOOKS better, and hopefully with work better.  I've taken some pictures and I'll get those on here ASAP.

WC

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Post by neali on Thu Jul 02, 2015 1:32 am

Wildcat,

I am very impatient, sorry. You are doing a great job with this. I am a little freaked out and pleased that all these date codes are within a month or two of my birth. Smile Caps are on their way.

I have the clock radio power cord as well, but it doesn't get warm. Good on you for replacing it as I am too lazy. Don't use a three prong with a chassis earth unless it is the only three prong in your system and you bring all the grounds, especially record players, back to it and a star connection. I have had some nasty hum problems with phono stages.

Fantastic job, great photos.

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Post by Wildcat445 on Thu Jul 02, 2015 11:25 am

Neali, had it not been for you and my frau, I would not own a Concert Grand. I had no idea in this world that such a contraption existed until you and another member were talking about one on ARF one day. You encouraged me to find one, and you have been there every step of the way up until this very day. You helped me go thru the Imperial, which was more scary than the CG in many ways. You have taught me more about audio than anybody on the face of the planet. I owe you a great debt of gratitude that can never be repaid. This may be a good time to thank you publicly.

The power cord on my CG actually runs warm, and this even in the short amount of time I have run it. That cord typically gets stuffed behind the cabinet in use, and that did not seem safe to me. Changing a power cord is not going to change its "personality", so I did it. I'm not sure it helped anything except made me "feel" better. The original had paint on it, but was in good shape. It will make a good AA5 cord.

WC

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Post by Wildcat445 on Thu Jul 02, 2015 3:21 pm

The tuner and pre-amp sections of this instrument benefit from five filter capacitors.  Typically, one sees a filter cap before and after a choke, then the branch circuits are divided from there.  In this instrument, each branch of the B+ circuit has its own filter cap.  Since my Concert Grand is essentially a big radio, it employs eleven filter capacitors, when one typically sees two and possibly three in most radios, even large consoles.  I thought this was unique enough to mention.

WC


Last edited by Wildcat445 on Mon Jul 20, 2015 2:34 am; edited 2 times in total

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Post by Wildcat445 on Sun Jul 19, 2015 7:13 pm

I have the tuner and power supply chassis done and ready to go back into the cabinet.  I got some cleaning done, but I saw little good being done by getting carried away with a lot of polishing and detailing.  When I get the MPX adapter installed, the tuner will fade into oblivion as far as seeing it is concerned.  I have a new trio of JJ 12AX7's, but also found a trio of new, in the box Mullard 12AX7's in my "top secret" stash.  I forgot I had them.  I was there looking for something else and ran across them.  I put the Mullards in and will save the JJ's for "just in case."  I have some pictures taken and on my computer.  This may be a "work in progress" post with lots of editing to add pictures, so please bear with me.

The radio and power supply chassis as they came out of the cabinet.
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The business end of the tuner.  This has to be one of the easiest dials to re-string ever created.  You have loads of room to work and you can get to everything.  Those little metal guide wheels that guide the dial string on the corners are known to seize and derail the dial cord.  I removed the dial cord and put about 1/10th of a drop of turbine oil on each one of them.  Then I put the cord back on and checked operation.

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This rather hefty-looking motor runs the tuner when using the signal seeking feature or the remote control.  The dial string assembly has to be timed properly so that the motor will reverse when it comes to either end of the dial.  There is a little tang on the tuner wheel that hits a micro switch that controls this motor.  It all sounds more complicated that it is.  I pulled this motor out and lubed its bearings and made sure it worked.  All I could do was to test it for continuity.  I will further test it when I get to the Phantom Control.

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Another picture of the tuner drive wheel.  I'm not sure if you can see the little tang and the switch or not, but the switch is ahead and slightly to the inside of the wheel.

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The tuner and power supply chassis are mounted in this area.  You may notice a switch above the opening for the dial, right in the middle.  That is the switch for the signal-seeking tuner.  The plunger is gone that operates that switch.  I am "engineering" a fix for that little plunger.  Some I have seen are red, some are white, but they are typically missing.  My guess is that they were some sort of not-very-durable plastic.  Mine will be made from a chunk of 1/4" dowel rod with one end painted red and with a brad on the other end to keep the plunger from falling out the hole.  I have to complete that task before the tuner can actually be put back in.

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This is the power supply chassis.  You will notice that it is fairly shallow.  There is not enough room, depth-wise, to put a terminal strip under the chassis to mount the filter caps on.  Re-stuffing the can is the only choice I have.  Here I am covering the chassis in preparation for cutting the can in half in order for me to remove the insides.

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I use a magic marker to draw a radial line around the can.  This particular line is not very straight, but it does not have to be perfect.  I just use it as a guide.  I use a Dremel tool with a cutoff wheel to cut the can.  I try to make my cut no more than halfway up the can.  This gives me room to grab the insides and get them out, but leaves enough solidly-mounted remnants of the can so that I can work with it.  You may notice a line perpendicular to the other line.  This line is to index the can properly when I put it back together.

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The can is now cut in half, revealing the insides.  I grab the insides with a rag and twist gingerly until I feel the connections break.  All the capacitor is basically consists of a bunch of aluminum wound up and sealed with a wax and put into that can.  With a little practice you can feel the connections break.  You want to leave the connections under the can intact, with wires still attached.  This method works well with most can capacitors if they are not mounted on a PC board.

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The insides.  How this ever works is beyond me.

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If you will look down inside the can, you will see three holes I have drilled.  One larger one in the middle, with two smaller ones on the outside of that.  These are for the wires for the two 33uf @450 volt capacitors we will be installing there.  The positive wire for each cap will connect to the correct terminal and the negatives are twisted together and put thru the center hole.

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The next picture shows the two new filter caps installed.  First, a tidbit of information about the caps I used.  I used 33uf @450 volt radial Nichicon caps that are really skinny, about 3/8" in diameter.  Neali introduced me to these skinny caps when I redid my Imperial.  These things are the bees' knees for re-stuffing can capacitors.  One can easily put two, three or even four of these in a typical 1 1/4" diameter can.  The power supply chassis has a two-capacitor can, and the tuner chassis has a three-capacitor can.  Neali was good enough to get these for me from Mouser, since I can't navigate their website.  

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This shows the bottom side and how the wires are connected.

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For a little added support and to help stabilize the upper half of the can, I use a piece of toilet paper roll about an inch and a half long.

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Then the top half of the can goes back on.

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Then I dig out my handy-dandy roll of super-expensive HVAC tape.

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Using scissors to cut it, I measure out enough tape to go around the can, overlapping about an inch.  Then, starting on the backside of the can, I gingerly roll the tape out EVENLY (to lessen wrinkling) all around the can, overlapping on the backside of the can, so the seam is on the rear, and not easily seen.  Then, if there are wrinkles, I use a towel and flatten the wrinkles to make everything nice and smooth.  Unless you are looking for the repair, it is hard to see.

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Three caps re-stuffed in the cap can on the tuner chassis.  Same procedure as the power chassis.  See that little black capacitor sticking out of the shield on the IF strip, just to the left of the filter cap can? That is a capacitor that's in the circuit for the eye tube. It is a radial cap and has to be removed and re-stuffed in order for the repair to not look silly. I removed it, cut just the very bottom off it with my Dremel tool, bored the guts out with a drill press big enough for the new radial cap to fit in, then used black RTV silicone to seal up the hole. I installed it WRONG, had to take it back out and start all over again. There is a 4uf electrolytic under the shield that needs to be changed as well.

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Last, but not least, the new, improved, larger power cord.    

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Mullard 12AX7's in the tuner chassis.  I don't know if these are the "desirable" kind or just tubes. Two of them are in shields.  One just to the left and the other out of the picture to the right.  It makes no difference to me.  Tubes are tubes.  These test good, so I used them, since that was an improvement over what was there.  And they are "old."  We'll see if this was ill-advised or not.  I have a set of JJ's in reserve if these don't work out for some reason.

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Next up is finishing my repair of the signal seeking switch and installing the tuner and power supply back into the cabinet.  After that is the Collaro Conquest model F-200-C changer. I performed a few preliminary service operations on the changer when I first brought the instrument home.  The motor was seized.  I took it apart and got it freed up and running.  The changer works somewhat okay, but needs the touch.  I will remove and properly service the motor, replace the drive tire and put a new needle in its Electro-voice model 26 cartridge.  I have an S-600 for one of my other instruments on the bench as well, so I will make an order in to Gary at VM and get the things I need for both changers.

WC

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Post by Wildcat445 on Tue Jul 28, 2015 12:50 pm

I have had some quality time listening to my Concert Grand for the last few days.

I identified several known issues during the restoration of this instrument.
* several resistors that drifted high in value.
*leaky coupling capacitors.  Good-All caps are on the "suspect components" list.
*at least one filter cap that had spewed it guts out.
*four 15K resistors that were the wrong value in the feedback circuit.
*weak or shorted 12AX7's, including the cathode follower.
*dirt that had fallen under the motor board that found its way into the tuning capacitor
*someone has turned up the treble amps almost all the way up.

I may be criticized for not "aligning" and " adjusting" any more than I did.  I see no reason to dig into something just to show I can do it.  I wanted to disturb nothing more than I needed to.  There is both good and bad to the way I am doing the restoration.  Good in that I apparently addressed the issue (s) that ailed this instrument, and bad in that, by shotgunning the repair, I am not 100% positive as to just what specific component or components were causing performance problems.  Perhaps a composite of several components or all mentioned above.  There were four identified suppliers of tubes for this one unit.  RCA, CBS-Hytron, Sylvania and "British" possibly Mullard.  

The performance of my Concert Grand is now more what the Magnavox engineers had in mind when they designed this instrument.  It will never be accused of damaging drywall.  It was designed to be more discreet and only has 40 watts, give or take.  My firm belief is that anyone who claims to have "booming bass' on his Concert Grand has a different definition of the term than I do.  Magnavox went to great pains to eliminate the "boominess" on Concert Grand instruments.  I personally prefer a little "boom" to the bass, but the Concert Grand still produces pleasing bass.  The highs are crisp and defined. The bass if firm and strong.  I am running the treble amps a tad more than a quarter of the way up, which requires running the timbre control between half and three quarters on.  FM requires less timbre, phonograph more timbre, with tape input somewhere in between, again depending on material.  I understand that the MPX adapter will improve fidelity on FM somewhat.  Installing that component is a couple steps away, so we'll have to wait to confirm that.  

I can tell you that all the strangled output and tinny output is gone.  The transistor clock radio with a two inch speaker definition is a thing of the past.  Even my wife was impressed.  All she normally cares about is that she gets sound when she turns it on.  This instrument displays the normal FM drift while warming up, due in part to its nature, and due in part to no AFC and having to demodulate the modern digital stereo composite.  By changing the 6EA8 tube in the tuner to a 6GH8A, this drift is confined to once during the warmup period.  It likely will never be any better than that.  Again, my understanding is that the MPX adapter may help with this condition as well, so we'll see in due course, I reckon.  The tuner has a cheesy little loopstick antenna for AM, so an external antenna is required if you want AM to work.  FM needs an external antenna in this area as well.  My considered opinion is that folks who paid Chevrolet money for a stereo did not give two hoots about a radio.  They wanted the stereo record player and perhaps the stereo tape inputs.  This the Concert Grand delivers in spades.  The record player sounded fine before the restoration, so I see no reason for different results after.

I got the little plunger for the signal seeking tuner switch made and put in.  This simple repair turned out to be the biggest pain of the whole restoration so far.  It was in an awkward spot.  Everything seemed to be in my line of sight.  The lid for the record changer compartment, my bifocals, the whole cabinet for that matter.  I made the plunger too long, so it all had to come back apart and be cut off and repainted.  I settled on red for the color, since white stood out too much and neither the wife nor I cared for that look.  Red is actually more discreet in this application.  I took some pictures and will post them when I get a chance.  It works the switch and does not fall out, so all is well so far.

My last comment about performance thus far is this.  ANYONE who is running a Concert Grand in original condition is both running on borrowed time and is not getting all they can from their instrument.  Although build quality is second to none, some of the components Magnavox used in its flagship model are unfortunately cheap and low quality.  Resistors and coupling caps head this list.  Mine had a Mallory filter cap that had spewed its guts.  Just saying....

WC

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Post by Bill Cahill on Tue Jul 28, 2015 4:46 pm

If you want it to last, replace all paper capacitors, and, electrolytics. And, Good All caps were one of the worst made.

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Post by Wildcat445 on Thu Jul 30, 2015 2:13 am

There are certain aspects of the restoration of my Concert Grand that I could have used more/better information for. This little plunger for the signal-seeking tuner switch being just one. I would like to have known more about how to properly adjust and sync the treble amps. Why is there no adjustment for the bass amps? EXACTLY what is the procedure for aligning the dial pointer and the two tabs on the tuner wheel in order for the tuner to cycle correctly? What type of gain can be expected on each stage, particularly in the pre-amp section? I suppose this information exists somewhere, but I have not found where, nor have I found anyone willing to share should they possess such information. There was a lot of guessing involved with this job that I would have just as soon had documentation for. It has turned out okay so far, so perhaps all you need to do is guess.

The plunger I needed for the signal-seeking switch measured almost 1/4 inch in diameter. I got a 1/4" dowel at the hardware store, and it was too big. I started using drill bits to see what size the bushing was, which I should have done to start with. A 3/16 bit fit perfectly. Then I had to find something that was 3/16" in diameter that I could work with. All I found locally was an aluminum rod 24" long. They wanted almost $8 for it, but I'm cheap. All I needed was a piece about an inch and a half long. I could not find a 3/16" wooden dowel anywhere. Perhaps this could have been sourced in the big city, but I live in Bugtussle, where you get what they have, or you don't need it anyhow. If all else fails, fall back on your junkbox, right? So I started digging. I did not want to machine a metal piece. I finally found an old broken Zenith TV adjustment tool. It was originally almost a foot long, made to adjust whatever in the vertical chassis Zenith TV's. It was a remnant of my stepdad's TV shop. I cut a chunk off this adjustment tool, and it was a perfect fit for the bushing in the Concert Grand cabinet. I made my cut more accurate, and filed the end so it would not be really flush, but rather beveled on the edges. It appears to be made of some type of stiff plastic, maybe even asbestos (?). It sawed easily with my Dremel tool. I put the piece, about 1 and a half inches long, in my vice, protected by a small piece of vacuum line to keep me from crushing the plastic. I heated the end of the plastic piece with my heat gun, then using a blunt brass drift and a ball-peen hammer, I swaged the end of the plastic piece. Just enough to make it bigger on the end, but not enough to swell the entire length. I tested it in the cabinet and it was not quite big enough on the end. So I repeated the process, being a tad more forceful this time. That did the trick. The shaft worked smoothly in the bushing, but the end was large enough that it did not slide out of the hole. I put the switch back into the cabinet and tried the entire assembly. The shaft was really too long, and the wife and I were not happy with the white color. It looked out of place on the cherry woodwork. So out came the switch again so I could shorten the plunger. I took almost 3/8" off the length, then painted the outer half of the plunger red. Radio dial pointer red. The red color correct for the dial pointer in a 1955 Buick Sonomatic radio, exactly. I got it at Hobby Lobby. It's in one of those little glass jars in the model car section. I had seen exactly three Concert Grand instruments up close and personal, and all three had missing plungers for the signal seeking tuner. I had a gentleman on a radio website send me a picture of his instrument and the plunger on it was white. I have also been advised that some were red. We have already been there.

I let the red paint dry a day or so before I put the plunger back in. I did not want the paint to be sticky and cause the plunger to weld itself to the cabinet. The final product, although TECHNICALLY incorrect, perhaps, works okay and I'm satisfied with it. It is one and a half inches long minus about 3/8's of an inch. I have already shared what a pain that switch was to put back and take out again, so that will be enough whining about it. If it was easy, everybody would do it, yes? The signal-seeking feature of the tuner works when the Phantom Control is on. So I will have to wait until that system is up and running to find out if the signal-seeking feature actually works. I'm thrilled with progress thus far, and I have pictures of this procedure loaded and ready to put on here when I get a second. Thanks for your interest.

WC

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Post by Wildcat445 on Thu Jul 30, 2015 12:32 pm

Here are the pictures, hopefully, of the little red plunger project.

This is the first run after I cut it to approximately 1 and a half inches long.

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I installed it back into the cabinet and checked operation with the switch.  You can see that it was really too long, and the white did not look all that great against the cherry wood background.

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After pulling the assembly all apart again and cutting the plunger off about 3/8ths of an inch.  I painted the end of it red in hopes of its looking better.

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The plunger and switch are re-united.  The wife and I both feel that the red is a better choice, original or not.  This is not something that could not be changed in the future.  

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There is a lot of electronics crammed into a relatively small space.  Room to work on the signal-seeking tuner switch is fairly tight.  These big Magnavox instruments with the tuner horizontally mounted on a board are easier to work with than the smaller instruments with the vertically mounted tuner.  Lead dress seems to be the Achilles' Heel on Magnavox, along with chassis ventilation on some models.  This particular Concert Grand has the coolest running transformers that I own in any Magnavox instrument.  Some consideration was given to ventilation, although the cabinet back is not well-designed for ventilation.  Typically, the rectifiers sit in close proximity to the power transformer.  These rectifiers are more isolated from the transformer, and the ventilation cutout is directly under the transformer.  Why this could not have been done with other instruments is anybody's guess.  

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I am in the process of designing a better-ventilated back for the cabinet of my Concert Grand. I'm thinking of using either tempered Masonite or lauan for the material. I need to source perforated metal somewhere to make ventilation panels. I want these ventilated panels to follow the outline of the various components, both so I can see all those tubes glowing and so air will flow better. I would retain the original back panel in case it was needed sometime. I might actually make this modification on all my Magnavox instruments to aid with cabinet ventilation. My Concert Grand is pulling 3.8 amps at 118.6 volts from the line for a total of approximately 450 watts dissipated. This is without the record changer on and without the Phantom Control on. These components should add approximately 60 watts, so my total will be something like 510 watts total. This instrument puts out a lot of heat in operation, as one would expect.

WC

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Post by Wildcat445 on Fri Aug 14, 2015 1:33 pm

Life has intervened into my Concert Grand project. It seems like forever since I have made any real progress on this project.

I finally have the changer parts I needed and have them installed. A new drive tire and a new needle for the cartridge is all I really did to the changer. I had done a partial restore just after I brought the instrument home. It works well enough to suit me. I'm sure it will develop a "personality" after I use it a bit, but that's fine with me. I may use it a dozen times the rest of my life. I have newer, more competent machinery to play my LP's on, so this changer will be just to show interested parties that it still works. I am not disposed to tearing this changer down to the last part and putting it back together in order to achieve perfection. I dislike working on record changers, do not consider myself good at it, so I do the bare minimum and go on. This record player sound pretty good, considering its age. I'm satisfied with it.

The next step is the MPX adapter. I believe I have a workable plan to mount it in the factory recommended location, but just not on the cabinet back.

WC

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Post by 75X11 on Fri Aug 14, 2015 3:02 pm

In your previous pictures, it looks as though convection would make your turntable the upper vent. Maybe that is why the lubricants seem to fail as often as they appear.
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Post by Wildcat445 on Sat Aug 15, 2015 12:48 am

This turntable does reside above the tuner chassis, but is reasonably isolated from the heat of the amplifier chassis. I am of the impression that it does not serve as a heat sink, like is typical of many other Magnavox instruments. The F-200-C changer does not utilize rubber motor mounts. The motor is mounted solidly to the motor board. This eliminates the one greatest cause of the changer not running right. When it comes to changers, I believe in the old "if it ain't broke, don't fix it" theory.

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