Author Topic: New (Old) Magnavox  (Read 2930 times)

electra225

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Re: New (Old) Magnavox
« Reply #75 on: April 14, 2019, 08:48:26 PM »
I typed a response to this thread on my phone on my lunch hour.  I hit the wrong button and lost it all.  I have no idea how kids type so quick on those things.  I like to never found the comma or apostrophe.  No wonder people who type on those things never use punctuation.  I won't make that mistake again.   :-[ ;)


Insulated terminal strips are available, but most I've seen or used have the lug where the bolt passes thru connected to chassis.  This is the lug you can use for common negative, the place where all the negatives of the power supply electrolytic capacitors connect.  If you have an insulated terminal strip, with no connection to chassis, use one terminal for all the negatives, then run a wire from there to one of the loops where the original filter cap can runs thru the bottom of the chassis.  The center tap of the power transformer is connected to chassis.  Common negative on your amp is the chassis.  So, really, you could connect the negatives of the power supply filter capacitors to anyplace on the metal chassis. 


Using a solder sucker is an acquired skill.  And one you should consider if you are going to work much with electronics.  It is not good practice to allow solder to blob or fall wherever.  It's a bad habit to get into, much like drinking and driving.  You should learn to control melted solder and to account for every drop.  I use my predominant arm for running the solder sucker and the other hand for the soldering iron.  You can also use desoldering braid if that would work better for you.  It is a tinned braid that will attract solder when it melts.  When it is soaked with solder, you snip the end of the braid off and start again. 


Chris has you straightened out on identifying which end is negative.  If you refer to the pictures I posted, you should be able to get a better idea what you need to do if you restuff.  You bore small holes for the positive leads to connect to their terminals and bore a larger hole for the negatives to pass thru.  I typically connect all the negatives inside the can, then run one wire from them to where it connects to common negative.


You'll be fine.  Just take you time and have some fun with it.  It took 50 years to mess it up, taking a week to fix it won't hurt a thing!  Good luck.   :) :) :)
I don't need Google.  My wife says she knows everything.

MikeD

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Re: New (Old) Magnavox
« Reply #76 on: April 18, 2019, 05:03:13 PM »
Well I pretty much have everything hooked back up. It was more of a pain than it should have been due to the fact that I wanted to mock everything up as best I could to see how it would all look and fit.  I then soldered one terminal at a time and left the negative ends run free. Then I connected three of the leads together and grounded them at the center(bolt hole) of one of the terminal strips. The cathode bypass is grounded separately near the original spot at one of the mounting lugs for the can.

The reason I mocked everything up was I wanted to be satisfied that I could get to everything if I needed to do any future work. It may look a little hokey but the new caps are mostly over open areas and do not cover anything up and also staying clear of the tube areas underneath.

All is now soldered and I have checked and rechecked them , comparing to the original mountings and the schematic. I will probably do this again tonight or tomorrow. I was and am still a nervous wreck , but it did go fairly well.

If I would not have screwed up and gotten axial instead of radial leads it probably would have been easier and looked somewhat neater.  Overall I think it looks OK and it will be hidden anyway, definitely not for the purist ;)

TC Chris

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Re: New (Old) Magnavox
« Reply #77 on: April 18, 2019, 06:52:21 PM »
If you are worried about possibly screwing something up inadvertently--I always am--then remember the famous dim-bulb tester and its many virtues.  It is nothing more complex than an incandescent bulb in series with your device.  The higher the wattage, the lower the bulb's resistance. I will usually start with a 75 watt bulb and then try 100.   If you get full brightness right away, you've got a short, effectively, somewhere.  The bulb should start dim and brighten as the filaments heat up, the rectifier starts to conduct, the electrolytics charge, and the other tubes start to conduct.

Chris Campbell

TC Chris

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Re: New (Old) Magnavox
« Reply #78 on: April 18, 2019, 06:57:54 PM »
I forgot to add...stop beating yourself up about radial vs axial.  I sometimes buy the "wrong" type when they are cheap or when the other kind isn't available and I want 'em right now.  With minor work-arounds, either kind can fit in almost any situation.  Just be creative.  And remember, these are under the chassis most of the time, so nobody's going to be seeing them and thinking "What a dork, he bought the wrong kind of capacitor."  I know there are perfectionists who aim for perfect replication of the original.  In cars, they will replace original factory assembly-line markings.  Noe of my cars are that perfect anyway.  Same with my electronics.  I try not to mess them up irreversibly, so some future perfectionist can replace my work with perfect work, but beyond that, I am for good function and sound work practices.

Chris Campbell

electra225

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Re: New (Old) Magnavox
« Reply #79 on: April 18, 2019, 10:12:53 PM »
Before you power up, we can take resistance measurements from the positives of the new filter caps to common negative.  You want to see a high reading, close to or over 1 meg ohms.  If you see a lower reading, say, 400,000 ohms or less, you have a "short".  That measurement will let you find out what the rectifier is "seeing" as far as a load is concerned.  If all is well, we can power up with some type of device to measure current, such as the dim bulb Chris suggested.  This sounds more complicated than it is.  This is like putting points and condenser in your Chevy engine, then checking the timing and dwell.  Part of the procedure.  We'll take you thru it exactly when you are ready.  You'll be fine.   :) :)


When you measure resistance on the filter caps, you will notice the value increase as the batteries in your meter charge the caps.  Reverse the leads and you'll see the caps discharge, then charge again.  This is how they are supposed to work.  They might start out at 50,000 ohms and charge to over 1 megohm.
I don't need Google.  My wife says she knows everything.

MikeD

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Re: New (Old) Magnavox
« Reply #80 on: April 19, 2019, 07:14:45 AM »
Guys, I have to admit I have never used any kind of tester, dim bulb or otherwise. The meter I have just reads 1 no matter what I check. I tried it in almost every setting , nothing. The bulb seems to be less complicated but where and how do I put it? I may put the tubes back in later  although I wont plug it in yet. My insurance is paid up ::)

electra225

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Re: New (Old) Magnavox
« Reply #81 on: April 19, 2019, 09:02:53 AM »
You'll need some type of reliable meter.  Might I suggest you go to Lowes' or Home Depot and get one of those cheap analog meters they sell.  It does not have to be anything fancy.  The reason I suggest an analog meter is that it is not so easy to become confused with an analog meter.  Displays on digital meters bounce around.  You can see the needle on an analog meter and know whether it is working or not.  I have a little green analog meter that I gave less than $20 for.  Those meters are called multimeters or VOM's.  (Volt-ohm-meter).  Don't populate the "vacuum bulbs" just yet until you make sure what you did is correct.  This is not a criticism of your work.  It is a part of the procedure that should be done following the replacement of filter caps.


We will walk you thru Meter 101.  It is not all that tough.  Now, Oscilloscope 101 is more complicated and is a skill I have not yet mastered.  To measure resistance, you would set the meter to "ohms" on a high range, put the red probe on the cathode of the rectifier, and the black lead on common negative, where the negatives of the filter caps are connected.  This will allow you to measure what load the rectifier is working thru.  If you get a high reading, up around 1 megohm or so, you should be golden.  If you get a low reading, under, say, 400,000 ohms, you need to check your work for miswires.
I don't need Google.  My wife says she knows everything.

MikeD

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Re: New (Old) Magnavox
« Reply #82 on: April 23, 2019, 07:19:42 AM »
It looks like I am ready to put the amp back in. I went over to my father's place on Sunday and we checked over my work. Also checked most of the resistors, two of the 220K were actually a touch low at 217 and 219, one was high at 245. Everything else seemed fine he said and also seemed to think the 220k were within tolerance. I may replace the high one before I give it the smoke test. I do feel a little better trying it out now. I will let you know how it works out.  I am not ordering any turntable parts just yet ;)

electra225

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Re: New (Old) Magnavox
« Reply #83 on: April 23, 2019, 09:13:24 AM »
Sounds like you have done fine!   :) :)

Music is just around the corner!   ;) ;)
I don't need Google.  My wife says she knows everything.

MikeD

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Re: New (Old) Magnavox
« Reply #84 on: April 23, 2019, 03:59:01 PM »
I have music. Everything is hooked up and it is working ; tubes are all lit up and nothing is smoking . I still have to address the antenna as I am having trouble picking up stations only 20 miles away. Some however come in crystal clear . It is in the center of my house (concrete block construction) so that I may need to hook up an external antenna of some kind and route it outside somehow. This may be an issue  when I put a metal roof on later this year.

Thanks for all the help, to put it in musical terms , you guys rock ;D I may get an order together for the changer in the next few days. Right now I'll just listen :)

Bill

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Re: New (Old) Magnavox
« Reply #85 on: April 23, 2019, 04:07:07 PM »
Congrats Mike!  Having success with ones projects has too be one of the best feelings in life.  Here's to many years of listening pleasure.   ;D

Bill

electra225

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Re: New (Old) Magnavox
« Reply #86 on: April 23, 2019, 06:56:17 PM »
Congratulations!  You deserve a lot of credit.  You did well!  Now you are hooked.   ;) ;) :) :)

The internal antennae in a Magnavox is extremely directional.  Turn the cabinet 90 degrees and see if performance improves.  If it does, install an external antenna and rotate it as necessary for best performance.  Apparently people who sprung the big money for a Magnavox did not care about the radio.  They wanted the record player. 

Refresh our memories about what trouble you were having with the record player, if you would be so kind.  And, again, great job and congrats!!   :) :)
I don't need Google.  My wife says she knows everything.

Bill

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Re: New (Old) Magnavox
« Reply #87 on: April 23, 2019, 07:41:01 PM »
Mike,

I have a request:  Could you please take a few photos of your Magnavox.  We all would love to see your new toy.   :)

Thanks,
Bill

TC Chris

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Re: New (Old) Magnavox
« Reply #88 on: April 23, 2019, 10:46:44 PM »
As to the antenna, it's extremely important to FM performance.  You can buy one of those T-shaped twinlead dipoles fro a buck or two and mount it all stretched out on a piece of lath or lattice.  Raise it high and rotate for directionality. Don't just dump it in a pile behind the equipment.  I have one on a stick hanging from the fire sprinkler pipe in my office at work.  At home, I've got  a small rooftop Yagi antenna aimed at my favorite public station.  Sunday nights I'll unhitch that one and use a smaller antenna in my living room that picks up the public radio station with the blues show, which is in the wrong direction for my rooftop antenna.  Antennas matter a lot.

Chris Campbell

MikeD

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Re: New (Old) Magnavox
« Reply #89 on: April 24, 2019, 06:27:05 PM »


Refresh our memories about what trouble you were having with the record player, if you would be so kind.  And, again, great job and congrats!!   :) :)

The tone arm stops advancing, sometimes anywhere on the record or at others reaching the end and not advancing into the runout. If I nudge it forward it will enter the run out track and then shut off normally. When I first bought it I did have the changer out and cleaned it up without removing too much of the mechanicals. I am more hesitant on tearing down too far than I was working on the amp( way to many tiny parts). I plan to do another cleaning and lube and also replace the drive wheel.