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Consoles => Magnificent Magnavox => Topic started by: 19and41 on December 23, 2017, 04:28:11 PM

Title: 1963 Danish Classic
Post by: 19and41 on December 23, 2017, 04:28:11 PM
This will continue from the Topic "Unknown Model".  Fortunately, both the capacitor replacements for the demultiplexer were delivered as of yesterday, and I am now replacing those.
Title: Re: 1963 Danish Classic
Post by: electra225 on December 24, 2017, 05:17:07 PM
The two little electrolytics? 
Title: Re: 1963 Danish Classic
Post by: 19and41 on December 24, 2017, 07:28:25 PM
Yes.  I replaced 1 and the other was a mylar wrap.  It should have been an electrolytic.  Now to wait on another from Indianapolis.
Title: Re: 1963 Danish Classic
Post by: 19and41 on December 30, 2017, 04:46:19 PM
Today I removed the hardware from one of the sliders and tried some 0000 steel wool and the acetone/lacquer thinner it removed much of the pigmented finish, but the areas where the spill took place appears to remain darker than the unaffected areas.  The darkening is of a black color in the pores and a broader darkening of the area as though some oil like liquid had been applied.  Removing the toned finish reduces the contrast but it is there waiting for some finish to accentuate it again.
Title: Re: 1963 Danish Classic
Post by: 19and41 on December 31, 2017, 08:51:47 AM
Here's what the lid looked after drying out.  bear in mind that it's now dry, flat and unfinished. the darkened areas are close to the cabinet's finish but has blackened pores and this is without finish. The cabinet remains finished.

Title: Re: 1963 Danish Classic
Post by: electra225 on December 31, 2017, 11:06:25 AM
That is looking pretty good.  Have you considered using Van Dyke brown or black grain filler and try to hide the rest of that?  What type of finish are you considering for the cabinet?  Would you consider trying 320 grit sandpaper on a block GINGERLY, and see if some more of the stain disappears?  The steel wool/acetone method was a good one as a first step.  I would not worry about the slider in the second picture.  Dark grain filler will fix it.
Title: Re: 1963 Danish Classic
Post by: 19and41 on December 31, 2017, 11:24:06 AM
Well, at this time I didn't want to refinish the cabinet, just clean it up somewhat and the grille cloth is looking quite acceptable too.  The undone slider has more darkened area to it.  I just need a way to get a consistent color on the sliders without having it look like I spilled something on it, or conversely having it look like i got the sliders from a darker color set.  I can't get it in a picture, but the sliders look like someone spilled a bottle of furniture oil, making a irregular puddle on each slider and the rest is dry of the oil, if you know what I mean.  The final finish with no other alterations will exaggerate that effect, and I will have a well preserved spill damage beneath the finish.  I might seem awfully tentative on the solution, it's just that the result will be pretty much permanent and  I want to do the right thing.
Title: Re: 1963 Danish Classic
Post by: TC Chris on December 31, 2017, 12:17:28 PM
You can always use some bleach in darkened areas.  I usually use regular Clorox, although you can buy an oxalic-acid bleach made for wood if you're really serious. 

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: electra225 on January 01, 2018, 12:29:26 PM
Perhaps if you refinished that top edge of the cabinet like you refinish the sliders, any "cheating" to clean up the sliders might not be noticeable.  We had a rule in the classic car business.  "Highlight what you are trying to hide."  If you have a hubcap with a slight ding, put it on the left front.  The car show judge will never see it.  Why? He is expecting it to be on the right rear, where he finds a perfect hubcap.  Same with bumpers.  ALWAYS rechrome the rear one.  A judge will never look closely at the front one.  He EXPECTS it to be perfect, so no use to look.  If the top of the cabinet looks nice to you, the rest always will.   ;)


Be careful using bleach on the sliders.  The veneer is over masonite.  If you get the masonite wet thru the veneer, you may be majorly screwed.
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 03, 2018, 06:06:33 PM
I don't want to do any refinishing on the cabinet proper,  but I could use some pointers on removing the surface dirt from it's top surfaces.  I did the other slider and followed up with wetting them with the solvents and wiping them down.  The final capacitors have come and I can finish the MPX.
Title: Re: 1963 Danish Classic
Post by: electra225 on January 03, 2018, 08:15:49 PM
I might suggest using waterless hand cleaner, the kind without pumice.  Put some of the cleaner on a pad of 0000 steel wool.  Rub gently with the grain.  The steel wool will work with the cleaner to remove a surprising amount of dirt.  After you feel it is clean, use a damp cloth to remove the residue.  When you get it clean enough that nothing comes off on the rinse rag, let the cabinet dry well.  Maybe a couple days.  Then give the work a good coat of furniture wax and rub it out well.  Good luck.
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 03, 2018, 08:42:28 PM
I still have some from the hepplewhite.  I'll try that. Thanks.
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 14, 2018, 11:26:20 AM
Seems like every weekend the cold moves in.  Can't get very much done in an unheated garage.  I have used pigmented oil on the sliders.  They are dark but they match without much of the splotchiness that they had.  I used the hand cleaner and steel wool on the cabinet and it cleaned and shined it up nicely. 
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 21, 2018, 03:02:36 PM
When I disassembled the unit, I carefully took pictures of all of the interconnects to make it easy to get things back together.  When I started reassembling the unit, I found that the SD card had failed in the camera.I am trying to set it up in a way that it may work, but I can't get any audio out of the unit.  I have had some help on it.  but the reciever, a 7909-10 is not marked like anything my helper nor any schematic representation shows.  All I have as a reference is the original as-built drawing.  Mine has the MPX modification and I'm not sure how it is to be connected.  I have also finally found it's tag.  It is a 1ST621
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 25, 2018, 11:03:06 AM
Had some off time and started by toning out the speakers.  They are fine.  I inspected the aamplifier for any wiring errors, found none and put it back into place and connected just the receiver to the molex trunk and connected my receiver substitute to the amp input .  It played through just fine, so as I have already tried the receiver directly through to the amp.  The problem lies with the receiver and or MPXassembly.  The controls on the receiver are just fine.
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 25, 2018, 11:52:34 AM
It appears the receivers' 6EU7 AF output tube has failed.  Ordered another.
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on January 26, 2018, 09:38:57 PM
6EU7 !!!   RCA was really  being defiant with their newer tubes pinouts.   Their 7027 (   improvement of 6L6), their 7199  (6U8 improvement )  and 6EU7 (12AX7 improvement)  had different pinouts than the older types that were standardized for ten or more types each.  They claimed benefits like less hum from better wiring possible, or improved screen grid heat dissipation from 2 pins per grid
but I think it was plain old ego like Edison using vertical recording instead of everyone else's lateral when he went from cylinders to disks.  Hope you are able to get your tubes and maybe some spares too.   Ed
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 26, 2018, 10:27:43 PM
The tube seems to make sense also in light of diminishing the size of electronic devices.  They have held up well, also with this being the second aftermarket tube in the console, after the rectifier.  It will be an aftermarket tube too as I am not going to pay through the nose for a Magnavox roll stamp.   ;D
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 27, 2018, 09:24:29 PM
I guess sometime next week I'll be able to finish off the electronics.  I am making arrangements with Habitat For Humanity to take the sectional and coffee table.  Then I can move the console in.
Title: Re: 1963 Danish Classic
Post by: electra225 on January 29, 2018, 12:51:28 PM
Using the horrible 6EU7 tube is one of Magnavox's Achilles Heels.  The older tuner/amp setups and the bi-amps used the 12AT7 and 12AX7 instead of the 6EU7.  Low noise, my foot.  The 6EU7 can cause all sorts of odd problems.  The suffer from heater/cathode shorts and get gassy when they get really hot.  Many factory-branded Magnavox 6EU7's are made by GE.  I have been told that RCA and Sylvania supplied them as well.  Sylvania tubes seem to hold up better and have fewer problems.  They never made a good 6EU7 in my opinion.  Every one is suspect.  Magnavox started using the 6EU7 the same time they started using the 6CA4 rectifier.  Fortunately, they had better luck with the 6CA4's. 
Title: Re: 1963 Danish Classic
Post by: TC Chris on January 29, 2018, 08:56:29 PM
So what was the rationale for changing from established successful tube types?  Gee, Magnavox stuck with 6V6s forever and didn't seem to feel the need to experiment. 

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 29, 2018, 10:25:59 PM
They changed their tube lineup in the stereo amp/power supply as well.  I would imagine it was just new series of tubes introduced at the time and it also appeared to have some European influence in tube design.  Multiple function tubes were a matter of some interest, though they were in use during the '20's and '30's in Germany.  1960 seemed to be like the millennium as far as starting with a clean slate and brave new ideas.
Title: Re: 1963 Danish Classic
Post by: TC Chris on January 30, 2018, 12:11:42 AM
I can understand things like the Nuvistor, but sometimes we seem to value innovation simply for its own sake without regard for substantive improvement in function.

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 30, 2018, 07:17:46 AM
You seem to have captured the 1960's in a nutshell.   :D
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on January 30, 2018, 06:59:07 PM
       I agree with you all concerning the "change-for-the-sake-of-change" mentality that a lot of people, young and not-so-young, embrace. They enjoy stirring the pot just to take an unpopular view and draw attention to themselves, Sadly, these people often get the lion's share of promotions and recognition,  from publish-or-perish academics to planners of obsolescence in cell phones or computer software.
      There's a timeless beauty in something like a 70 year old Magnavox chassis (which 99 % of their owners never saw) with the warm glow of filaments and cathodes, the softly lit glass dials, even the richly colored components and wires under the chassis. If the full EIA color code was followed you could do a lot of troubleshooting without a schematic. Or the record changer compartment which lit when you lifted the lid. Or the red jewel that told you power was on when all lids were closed.
       Compare all these visual treats to an all transistor chassis with circuit boards that looks like its not even plugged into the AC power. No wonder kids aren't interested in electronic audio these days.
        Had to get that off my chest. I can't wait to get the first sounds out of my recently acquired CR-155 chassis.
Title: Re: 1963 Danish Classic
Post by: 19and41 on January 30, 2018, 07:29:06 PM
I know it's sacrilege to many here, but I think I would have been about as happy with a solid state unit. (my dad had one and it performed well) I do like the look and feel of tube architecture though, but after all, the music is the thing for me.
Title: Re: 1963 Danish Classic
Post by: TC Chris on January 30, 2018, 08:15:44 PM
Agree on the quality of the music as the first consideration.  My living-room system is modern and solid-state.  It's all fun to play with.  And I also agree with the romance.  One of the wonderful things for me to contemplate is driving down the road late at night in an old car, AM radio edge-lighted slide-rule dial glowing in the dash off to the left, bringing me some good music or some news from way, far away.  There were times in grad school when that little fantasy got me past a pile of anxieties and worries.  And I've said before, there's still something magic about picking these tiny signals out of the air and hearing music from them.  One more thing for me is the wonderful variety of ways to get to the same result.  The goal?  Receive and detect a signal we can hear.  The method?  A gazillion different approaches to Rf and AF design.  Most rely on common principles but there are different ways to implement them.  Save a penny here, or add a dime there to get a boost in performance.  It's why I never turn down a radio or audio device.

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on January 30, 2018, 08:31:57 PM
Yes, that's true, when Magnavox went transistor, they retained all the traditional style of their tube consoles, such as the edge lit glass slide rule dial, pilot lamp, sliding lids, etc. My mother's Astrosonic, given to her in '67 by my grandfather, is in my living room now and its never been worked on.  I never dared take it apart any more than I would take apart her piano.  It spent it's first 60 years in the same living room location up against the hot water baseboard. Magnavoxes are like upright pianos. They plant themselves into the carpet and once in the sockets, they never leave the spot, like the dining room credenza. Like the seventh blue Buick sedan in a row. in the garage. Predictable.
Title: Re: 1963 Danish Classic
Post by: electra225 on January 30, 2018, 11:06:08 PM
I have my third black Buick out in the garage....... ;) 


 
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 10, 2018, 02:49:01 PM
Just finished Putting the unit back together.  Listening to Kenton In Hi Fi.  It was worth the trouble.  I've set up a temporary turntable to use with it.  The thing sounds just great!
Title: Re: 1963 Danish Classic
Post by: TC Chris on March 10, 2018, 05:31:04 PM
Lookin' good!  Wish there were a way we could all hear it!

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: electra225 on March 10, 2018, 07:14:42 PM
I'm glad you got it going.  Do you plan to go thru the original Collaro changer at some point?  That certainly is a handsome instrument.   :)
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 16, 2018, 08:11:39 AM
The changer will be coming up.  When I did the initial tryout for about an hour or two, the FM section's tuned frequencies drifted a great deal and remained so after having it turned off for a day.  It is as if the tuner's spread was divided in half, then positioned so the two ends met in the middle with the centers at each end.  Regardless, I will have to pull it again and replace the C2 electrolytic on the FM board, then I will do an alignment on it.
Title: Re: 1963 Danish Classic
Post by: Bill on March 17, 2018, 10:32:27 AM
Very nice Rex. Once you have all the bugs our it should bring you many years of enjoyment.

Bill
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 17, 2018, 05:56:21 PM
It looks like this is going to be a deadly bug.  The problem lies in the FM tuner.  It is so far out of it's operating range, the IF's have no effect on it.  I'm missing about a 1/3 of the FM band.  My favorite station 90.1 is at the top lock of the tuner.  That's off the scale, above 108 Mhz.  I've tried all afternoon with no luck.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 17, 2018, 08:56:48 PM
Is the string pulling the tuner all the way from one end to the other?  Are the plates (or plungers) fully meshing and unmeshing?  Does the AM tuner track properly?  My experience with these is that the pointer moves somehow (slides on the string) and does not allow the tuner to move completely.  You might take the pointer off then try the tuner and see if that makes a difference.  Sams gives the details of how to set the pointer back on right.  Good luck.
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 18, 2018, 05:15:28 PM
Mechanically, the tuner was going all the way to both ends.  The AM was working fine.  I decided to try an ace in the hole.  When the prospects of getting the reciever up and running was looking bleak, I got another reciever a few weeks ago.  Today, I went ahead and recapped it, I had to replace the dial glass as it was inverted to mine.  The same order, but the numbers inverted. I also pulled and inverted the meter.  It is a 1961 model and it has the RCA jacks together in the rear.  It  too is off freq. but I seem to have the whole band on this one.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 18, 2018, 08:43:28 PM
What do you suppose would be the fix for the original tuner?
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 18, 2018, 09:08:25 PM
I would imagine it is in the enclosed portion of the tuner.  Apparently there must be components that have changed value.
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 25, 2018, 12:03:30 AM
I believe I will go through the original tuner and check the resistors and the values of the capacitors and replace any that appear marginal.  I've just ordered both a ceramic capacitor and metal film resistor assortment.  The tuner in the console now is unstable in FM and will not balance correctly.  It's just usable, but not right.
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on March 28, 2018, 11:12:45 PM
      Just curious----if your unit is vacuum tube---which I assume it is because it's not Astrosonic, a gradual short between heater and cathode of the FM local oscillator tube (6U8 ?) will place extra capacitance in parallel in the tuned circuit which might cause your symptoms. You have to tune higher and higher just to get the low end stations.

    If your unit has FM-AFC there should be a small solid state diode in the oscillator circuit that might have wrong voltages on it which cause it to severely change capacitance. I don't know if Magnavox used the diode or a tube section as the AFC reactance tube to change the oscillator frequency

   I'm going to look at the schematic of the various FM tuner chassis, but there isn't much that can cause an oscillator to change frequency so drastically cuz at that high frequency, it's mainly an air wound coil and the air tuning capacitor so there's no dielectric or permeability to change ---air is air---and its weird that it happened while you were listening to it.
         Either the capacitance is increasing or the inductance is decreasing. The only way to decrease the inductance is to insert some sliver of copper or brass into the coil and you didn't do that. To increase capacitance you'd have to turn the adjusting screw way in or bend a lead close  to the chassis metal. A Q-tip dipped in ice water and held to each of the little ceramic capacitors near the tuning condenser might show up a temperature sensitive cap,...... or maybe the band selector switch isn't completely disconnecting the AM oscillator circuit when you switch to FM---metal dust between the contacts.
        I hope I can find something interesting in the schematic for you to check,
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 29, 2018, 08:00:26 AM
The tuner is covered in Sams 655-10. It appears that duringthis time frame, the physical layout changed a bit, but the circuit remained pretty much the same.
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on March 29, 2018, 11:25:57 PM
      I looked up two of the Magnavox AM-FM tubed tuner chassis and they both used triode-pentode FM oscillator/converter tubes, one a 6U8 the other a 6EA8. The triode local oscillator circuit had a "hot cathode" oscillator circuit where the cathode went tooo a tap on the coil instead of ground.
      If there was leakage or a cathode-to-heater short internal to the tube the added capacitance to the tuned circuit would send all the lower FM stations to the high end of the dial plus the tuner would lose a lot of sensitivity since the RF circuits would be way misaligned from the new, off=tune oscillator alignment
      I have no idea if a tube tester would find this tube bad.
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 30, 2018, 07:50:51 AM
My tuner uses 2 6DT8's for the FM RF amp and FM converter, a 6BA6 for the AM/FM IF amp and a 6AL5 for the ratio detector.  Your drawings may have been for earlier models.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 30, 2018, 09:07:53 PM
Magnavox used 6U8, 6EA8, and 6DT8 as an FM oscillator.  My thinking is they were working on the drift when these things were new.  A 6U8, 6EA8 and 6GH8 will basically interchange, according to my RCA tube manual.  The 6DT8 is used in the later, smaller tuners with AFC.  You guys are lots more technical than I am, but I can tell you what works for me, for whatever reason.  I subbed the 6EA8 in my two larger tuners with a 6GH8-A.  I had an old TV repair man recommend that to me.  My understanding is the 6GH8 was a common TV tube.  The "A" suffix tube was an improvement designed for use in chroma and color circuits of TV sets.  Using it instead of the 6EA8 did help with the drift considerably.  Now, especially on the CG, when you start the tuner, it is off station.  I set the station and it stays all day.  When I start it up again cold, the station has drifted.  That is better than running an hour, drifting off station, being readjusted and then run well without drift all day.  This makes me think the oscillator is drifting.  The strength of the station plays a part.  There is no direct substitute for a 6DT8.  Both of my sets with a 6DT8 have AFC.  AFC was a major improvement.  Do you notice the drift being worse when listening in FM stereo?






Title: Re: 1963 Danish Classic
Post by: 19and41 on March 30, 2018, 11:17:10 PM
The one that is in it right now doesn't drift. It is off frequency by 10Mhz.  It also has crosstalk when tuned to some stations.  The AFC will track with some stations but will not peak tune.  It just drops off, then I have to go back 3 or 4 Mhz where the station pops in again
Title: Re: 1963 Danish Classic
Post by: electra225 on March 31, 2018, 12:12:46 AM
I'll follow your progress with interest.  Never seen this condition before.  Could SMD be a consideration here?  I've never run across SMD in FM before.  You say AM works okay, right?
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 31, 2018, 07:11:20 AM
The way it's been described, I wouldn't think it was SMD  This just seems like some thing or things out of tolerance.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 31, 2018, 10:06:15 AM
The silver mica capacitors that suffer from silver migration (SMD) are of small value and, apparently, not very good quality.  Silver migration, per se, is what causes the "lightning crash" typically associated with SMD.  What if those little silver mica caps do not suffer from silver migration yet, but are simply drifted in value, enough to upset peaking of the coils.  Referring to the schematic, those caps are connected across the coils.  Possible ?   :-\
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 31, 2018, 10:36:46 AM
Probably.  I have just never heard of it affecting Magnavox equipment.  Nothing really dramatic has occurred other than the frequency shift.  If it were to definitely be the problem, I have an envelope of incy wincy silver mica caps I used in a Hallicrafters to correct the problem.  Today I am trying to complete a strut job on the Mustang.  The auto parts store sold me one bushing kit that had been robbed from. And they are tracking down the last one in Georgia.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 31, 2018, 01:20:05 PM
I have never heard of SMD in Magnavox equipment, either, and I pray I never do.  Magnavox IF cans are slug tuned, so they are the type that suffers from the condition.  Time is not on our side.  Your investigation may end up being more historic than your realize.  If SMD becomes a problem with Magnavox, I'll send you a bucket full of IF cans to fix.  My eyesight is not good enough.
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 31, 2018, 03:38:57 PM
I got out the original receiver and disconnected C7 on the IF/RF board as the photofact says to do.  the only adjustments that had any definite effect on the FM portion was 2 ceramic trimmer caps in the FM tuner assembly.  I was able to bring 90.1 FM from the top end to a bit below center. That's some progress.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 31, 2018, 03:49:18 PM
Do you believe there may be components that have drifted in value, or do you believe someone has been making "adjustments" at some point? 
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 31, 2018, 05:06:29 PM
Judging by it's condition when I got it and that I can't get it fully lined up, I'd say drift.
Title: Re: 1963 Danish Classic
Post by: electra225 on March 31, 2018, 06:16:01 PM
Are you suspecting capacitors C5 and/or C11?  I'm not sure what these caps do, but they appear to be across the FM tuning cap.


Another perhaps minor fact I just realized is that I did not replace capacitor C7 when I redid any of my tuners.  That is listed as a "stabilizer cap."  Significant?
Title: Re: 1963 Danish Classic
Post by: 19and41 on March 31, 2018, 07:36:36 PM
They're A13 & 14 on the photofact.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 01, 2018, 12:59:54 PM
You lost me.  Where is A13 and 14?  I don't see them...... :-[
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 01, 2018, 01:08:44 PM
Look at the illustration of the top of the entire chassis.  They are in the module on the lower right where the FM tuner string goes in and they are on top next to the FM ratio detector tube.  I thought I would try to loop another wind on the FM tuner cord.   90.1 FM is dead on.  It also comes up near the top end.  There doesn't seem to be any rhyme nor reason as to where the stations fall out on the dial.  I can't get a good idea where the trimmers are going.  They are too stiff to turn with a plastic tool and any metal throws it far off til it is removed.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 01, 2018, 01:28:35 PM
I printed out the schematic for my Imperial and for your instrument when you were going thru the tuner.  I was looking at the Imperial schematic....... :-[


I don't see any illustrations of the dial drive on the Sams.  Typically, there is a counterweight, then the guillotine tuner for FM is gear driven from the AM tuner.  I had one that was loose and the gear got mis-meshed, which threw the alignment of AM and FM off.  As I remember, AM was on, FM was off.  Again, as I remember, there were timing marks to get the gears meshed properly.  Could your FM tuner have jumped a cog?  Am radios with stations more than one place on the dial indicated an alignment problem.  You seem to have that covered.  Theories?


I have a "bone" alignment tool that belonged to my stepdad.  Made of some type of ceramic material.  It works real well for those stubborn trimmers. 
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 01, 2018, 02:36:28 PM
All of this info is on the folder I sent you a while back.  you should have the same one I am working from.  It's pointed out on page 6, the last one.
Title: Re: 1963 Danish Classic
Post by: TC Chris on April 01, 2018, 11:01:18 PM
When in doubt, try Google.  A couple weeks ago we tried to start my Mom's '97 Subaru.  My sister had not driven it, as she had promised to do. The starter gave a couple weak cranks and stopped. And the parking and dash lights started flashing.  I put the charger on and got the battery up but they still flashed.  We went for a drive and they still flashed.  We came home and turned the ignition off and they still flashed.  I disconnected the battery and left it undone (sometimes problems go away).  Today, two weeks later, I tried again.  Connect battery, lights flash.  @#$&*!!!  So my sister Googled it (she was off one model year).  Somebody had  posted, "look for the black box under the dash, find the black button, push and hold while turning ignition on."  I crawled under and found a button.  My sister turned the key.  There was some relay clicking (as the post had predicted), the door locks operated, and the lights stopped flashing.  It was a computer reset and it worked.  Bless Google.

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: electra225 on April 02, 2018, 04:10:30 PM
It's probably just me, but I have not had a lot of success finding help with Magnavox issues on Google.


I have had better success with YouTube.  I found out that I could replace the $145 dollar cabin air filter in my car for about $21 utilizing the information I got on YouTube and parts from Amazon.
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 02, 2018, 06:32:00 PM
That would just depend on which one carries the best tutorials.  I haven't seen anything that goes into sufficient detail to get a good result on this.  I am debating getting a digital PC oscilliscope.  I have a 10Mhz scope but The If on this is 10.7 mhz.  I need to apply the correct signal and monitor the result correctly.  I can get a 20 Mhz digital interface for under $65.
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on April 02, 2018, 11:29:04 PM
FM tuners usually have the local oscillator on the low side of the RF, ie 77 to 97 MHz rather than the high side 99 to 119 MHz cuz drift is lower when it tunes a lower frequency. If instead of tuning 77 to 97 MHz, it tunes 77 to 101 MHz, then it will get 90.1 twice on the dial, once whe the oscillator is at 79 MHz  (I'm rounding 10.7 IF to 11 MHz) and the second time at 101 at the tip top of the dial. Tuners misaligned enough to tune the low side at one end of the dial and the high side at the other end will have a big dead zone in the middle of the dial when it's changing over from low side tuning to high side tuning.
The thing to do is adjust the trimmer capacitor on the oscillator to send the 90.1 "ghost" sicnal even higher on the dial until its conpletely off the high scale above 108. If the tuner could go 88 to 112 instead of 88 to 108 then 90 .1 would come in at 90.1 and 112. The reason 10.7 was chosen as the IF in FM tuners is that there would be no image reception. If it was only 10 MHz, 88 would come in at 88 and 108,
   If you have the 12DT8 sealed slug tuned tuner instead of the 3 gang variable air capacitor tuner you may have mistuned slugs and I'm not familiar with them. I may have been lookibng at the wrong tuner downloads. 12DT8 was the tube that all those slug tuned jobs seem to be designed around. I  think the European designation is ECC85.
Good luck. Remember, getting 90.1 at the top end may only mean the oscillator is 4 MHz high, not 20 MHz low, and you are getting it as an image frequency
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 03, 2018, 07:22:54 AM
I think I will need to align using an input signal and electronically monitor the circuit.  Alignment to a station should be just for tweaking the circuit.  Let me look into this option.
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 04, 2018, 09:17:51 PM
I just ordered a 2 channel 20 Mhz oscilloscope interface for my laptop.  That and my signal generator ought to get things started.
Title: Re: 1963 Danish Classic
Post by: TC Chris on April 04, 2018, 11:24:38 PM
Tell more about your choice of the scope interface.  I've seen some references to those but have not studied the subject.  I assume it gives a very high impedance input, plus maybe a grid overlay for value reference?  What are the disadvantages compared with a real 'scope?

Chris Campbell
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 05, 2018, 07:43:27 AM
Here are the published specs on it.  I'll know more after I have used it.


USB2.0 interface, no external power source required, easy to use.

Be suitable for notebook computer, product line maintenance, be used easily on business.

Analog bandwidth: 20MHz / 50MHz / 80MHz / 100MHz

Channel: 2 Channels

Real-time sampling rate: 48MSa / s, 150MSa / s, 250MSa / s

Storage depth: 10K-60k / CH, 10K-1M / CH

Rise time: ≤ 7ns, ≤ 4.4ns, ≤ 3.5ns

Time base accuracy: 50ppm

Time base range: 4ns / div - 1h / div

Input Impandence: 1MΩ 25pF

Input sensitivity range: 20mV / div-5V / div

Vertical resolution: 8bit

Vertical displacement range: 10mV-5V / div @ x 1 probe; 100mV-50V / div @ x 10 probe; 1V-500V / div @ x 100 probe; 10V-5KV / div @ x 1000 probe

DC gain accuracy: 3%

Bandwidth limit: 20MHz

Trigger Type: Edge, Alternate

Trigger source: CH1, CH2, EXT, EXT / 10

Specifications:
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on April 05, 2018, 10:58:20 AM
       Sorry again-----I should learn to read better. I missed the part about your tuner having the 6DT8 entirely. Everything I wrote was with the air tuned capacitor and the 6EA8/6U8 tuner in mind. Those sealed inductance tuned tuners with 6DT8s are a total mystery to me and I have never dared adjust the oscillator part, mainly because I don't understand how they can make the converter oscillate, or the oscillator convert, depending on your viewpoint. One of the two tube sections does both, and the other section is a separate RF amplifier.
       I still think the part I wrote about lowering by 4 MHz the oscillator frequency at the 108 MHz side of the dial applies if you receive 90.1 at to two spots on the dial. It looks like A13 is the adjustment for high side oscillator frequency, at least that would be the adjustment with a variable capacitor 6U8 type of tuner, but with a variable inductor tuner A13 might shift the entire tuning band up and down equally.
         If you have a way to measure the AFC diode as a pure diode---say a Simpson  style VOM with an actual meter instead of digital readout===you might do that. An open cicuited diode would have much lower capacitance and shift the FM band several MHz up just like you're getting.
        Those variable inductance sealed tuners were used in a lot of higher-quality table FM radios with a 12DT8 being the only difference instead of 6DT8. If you find a donor chassis that works on FM, it would be a simple matter to do a transplant ??
          Good luck.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 05, 2018, 04:13:22 PM
As far as I know all the Magnavox tuners, certainly of the stereo era, use a "guillotine" tuner.  What about tuners without AFC?  I have read that the bandwidth of the tuner, and of the MPX adapter, is not wide enough to accomodate the digital, high definition stereo signal currently broadcast.  Let's assume for a moment that this is true.  Does your theory of oscillator performance address this issue?  Conversely, if the "bandwidth" theory proves to be so much bilgewater, now it the time to displace it, once and for all.  Your thoughts?
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on April 06, 2018, 02:27:46 AM
    I don't know if any of the original FM stereo standards have been changed to allow modulation closer to 100 % or to eliminate guard bands that helped older tuner designs work well even with simpler circuits. I used to hear classical FM stations mention that they are using Dolby B or Dolby C and that you should engage the Dolby switch if your tuner is equipped with it.
    What newer tuners and broadcast station equipment have in the way of encoded surround sound and other features might use the old SCA (originally for Muzak advertisement-free background music subscribers) frequency of 67 kHz which no old FM stereo multiplex or old ratio detector/discriminator could get, the better multiplex circuits even had filters to get rid of it and other unwanted ultrasonic signals that might cause birdies or beat tones when tape recording off the air. The older tape recorder mike channels had no filters for ultrasonic frequencies and interference with their own erase oscillators could occur.
      I think a high quality FM tuner from any era will put out high quality sound when tuned to a high quality FM station even if it is using modern enhancements like digitally encoded gain expansion or noise suppression or surround sound, but without those special features being activated. But...don't quote me on any of the newer stuff.
       The original FM spec was channels 200 kHz wide but modulation only 150 kHz wide to allow for real world tuned circuits that weren't totally attenuated to nothing between 150 kHz and 200 kHz. All the new tuners from the 70s on had one or more ceramic filters that really did have the sharp band edge cutoff that tuned IF transformers didn't have, but they had ripples in the passband which didn't affect the sound in an FM tuner, but these amplitude ripples also caused phase ripples that did distort the sound though slightly. A good old FM tuner with all tuned transformers supposedly sounds cleaner than an FM tuner with ceramic filters. (The same goes for speaker systems with simple series capacitor crossovers instead of 12 and 18 db/octave L-C crossovers in the high-power rated speakers.)
       To work well in todays crowded FM bands compared to 50 years ago when the entire band had 5 local stations, widely separated,  the tuner should have a lot of FM double tuned IF stages to have it's off channel response as far down as possible, plus a good AGC system like a good AM tuner would have. This allows strong unwanted local stations to not overload the weak desired station next to them. However......the limiters and detectors should be very wide band (I think Fishers have 1 MHz, Scott has 2 MHz, maybe even higher in brnds like Marantz and McIntosh) The wider the bandwidth of the limiter-detector circuit, the better the multipath rejection and adjacent channel rejection, signal to noise ratio and everything that makes a good tuner good. Magnavox used it in 1968 and later tuners and called it SSC or something like that Gotta give up the computer for a bit colntinued later
Title: Re: 1963 Danish Classic
Post by: ed from Baltimore on April 06, 2018, 05:07:25 AM
I'm back, had to give up the computer for a minute, so had to post without rereading to make sure i was making sense.
         So.....a disadvantage of the wideband limiter-discriminator is its low sensitivity, requiring either extra IF stages before or extra audio stages after. I think Magnavox tuners 1968 or later had what they called SSC circuits which were wideband although I don't know what the initials stood for. Strong local stations should sound as clean on the older Magnavoxs as on any tuner, depending  on the location and antenna.
        The two 6DT8 inductance tuned FM units I have seen differ in that one has an AFC diode and the other hasn't. I have noticed that a station that isn't audible can still grab the AFC and cause the station you are listening to shift to a distorted tuning point, making it necessary to leave the AFC off.
          I think 19and41s 63 console just has an RF alignment problem and isn't caused by any station features like digital high definition. The station can't even get into the IF stages and detector because the oscillator is not 10.7 MHz below the signal and the RF tuned circuit is not lined up to the station frequency.
          The modern FM station still must still stay in it's 200 kHz passband and the Magnavoxs 2 IF transformers will let it all through but the ratio detector circuit is probably barely wide enough. You can judge how wide or narrow your detector circuit is by tuning without AFC to the two points of worst distortion and judging on the FM dial the frequency shift. Say 101.3 to 101.5 covers the two worst points on a station, then your bandwidth is 200 kHz, and the linear tuning in between is narrower yet. The signal might not be so clean sounding if the station uses audio compression to allow the signal to continuously fully modulate instead of only on the occasional musical peaks.
       The multiplex circuits are standard AM detectors, although the carrier and sidebands dont come  from the same IF transformer like in an AM tuner, the carrier is the 19kHZ pilot tone from the detected FM signal, which has been put through a frequency doubler to change it to 38 kHZ and the sidebands are 23 to 53 kHz (38 +/- 15kHz) coming through tuned circuits fed from the same detected signal.
    Most AM detectors will not handle higher frequencies at high levels of modulation without distorting although they handle lower frequencies at full modulation fine. They can still use a standard detector circuit because the average musical signal has very little power at high frequencies, that's why tweeters can be low power speakers compared to woofers and midranges.
        If the FM signal difference frequencies are highly modulated at high frequencies, they will distort in most FM multiplex detectors. If the surround sound and other new features put encoded information on the otherwise little used high frequency multiplex signal, that might be why they say the older tuners will distort the signal.   
        Just as a guess, I'd say that most of the bad sound from these old tuners  isn't due to the digital high definition or whatever a modern station does to its music, but due to two shortcomings of the typical tuner:
    First, the crowded FM bands with adjacent channels fully occupied, tuned through too few IF tuned circuits and...
    Second the barely wide enough detector bandwidth, receiving a signal from a station using a lot of audio compression that causes the signal to be fully modulated  a large percentage of the time instead of only on occasional peaks.
      The signal compression isn't new, they've been doing it for decades, and its not digital or wide bandwidth. What might be new about it is
the degree of compression that's being done now. Also nearly every nonpublic station uses it instead of just some.
      Quality music from a quality station such as a public radio station that doesn't use compression should come through an old tube Magnavox as undistorted as ever. There is usually more spacing in the public bands also. The station may not sound as loud as the others, bu that's the others fault for overcompressing.   
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 07, 2018, 09:20:30 PM
Tried out some new items I got to help with the alignment.  I have used these type of tools in my work and thought they would do nicely on this.

https://www.ebay.com/itm/8-x-Anti-static-Ceramic-Full-Type-Adjust-Frequency-Screwdriver-Set-Hand-Tools/352188228370?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 14, 2018, 08:51:25 PM
I finally got the oscilloscope today.  It came at the same time as my metal film resistor assortment. I've been marking bins in some Harbor Freight compartment boxes to file them away.  It's supposed to rain tomorrow so I will try it out then.  The ceramic alignment tools work nicely.  I also found a box of 97 #1847 long life 47 bulbs for a really cheap price.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 15, 2018, 12:12:02 AM
Good luck with your new toys, Rex.   I'll watch to see what you find out with the alignment.  I hope it works well for you.
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 15, 2018, 07:59:23 PM
Well, I have a return order for the oscilloscope.  It wouldn't show a trace so there was no way to even know if the softpot controls were functioning on the "screen".  I went ahead and tried the CRT scope again and obtained a passable level and sync on the signal.  The original receiver would only allow for an increase in signal, but distributed over the grossly incorrect frequencies as shown on the dial.  Took the "new" receiver and disconnected the correction cap and with the injected  10.7 Mhz being drowned out by the FM stations in the area, I got a FM receiver so I could tune various stations and tried lining them up for strength and center at their dial positions.  90.1 is dead on and things are now pretty accurate and strong up to about 105.  If you are going to try this at home I would strongly advise the purchase of some ceramic alignment tools as these circuits are not tolerant of any metal and plastic doesn't have the strength.  I now have one more problem.  the right channel is about 1/4 to 1/3 the loudness of the left.  All the adjustment in the hollow tone shaft does is raise and lower the volume of the left speaker.  This is common to both receivers.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 15, 2018, 08:32:36 PM
Are you using the Multiplex adapter?  There are gain (volume) control(s) on the MPX adapter.  The two-tube versions have a gain control for each channel.  The three-tube models I have seen only have one.  I'm assuming it works somewhat like a balance control.  These controls are located on the rear apron of the Multiplex adapter.  Just an idea, that will hopefully help.  Good luck.


While you are in there, you might give the 6EU7 in the tuner a good wiggle.
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 18, 2018, 05:06:12 PM
The mpx adapter should only affect the radios audio,  shouldn't it? This also occurs with the auxiliary audio.  I have scrubbed the molex connectors and the speaker switch and treated it with deoxit.
Title: Re: 1963 Danish Classic
Post by: electra225 on April 18, 2018, 09:12:06 PM
The MPX is only in the circuit in the "FM stereo" position of the function switch.  Does the balance control have any affect on the situation?
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 18, 2018, 10:11:38 PM
I am used to the fader control on a stereo, in which the volume of each channel is adjusted mutually exclusively.  This  control increases and decreases the volume of the left channel.
Title: Re: 1963 Danish Classic
Post by: 19and41 on April 21, 2018, 09:26:46 PM
I have it together and am listening to my favorite Saturday evening program.  It is doing mighty well indeed!