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 Post subject: Re: Repair of a Badly Damaged (in shipping) Tefifon T574
PostPosted: Mar Thu 08, 2018 3:03 pm 
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Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Joseph Newton wrote:
Nice thread, thanks for keeping us updated. You just might be a miracle worker!

Thanks!

To be honest, I think the damage looked worse than it actually was. However, one still has to employ the right approach to fix that kid of damage. I knew I could do it because I have experience building and also fixing musical instruments. I also have the right tools and for tricky executions the right results cannot be achieved without the right tools. However, this job did not require any highly specialized tools that couldn't be purchased at any home improvement stores.

The only somewhat hard to find material that I've used was the wicking superglue. Home improvement stores do sell a superglue that is labeled "liquid" but it is in fact a gel. To to the right job fixing weakened particle board one really needs to use the wicking type. I don't want to place commercial links here, but I can say that Googling "liquid superglue guitar repair" will get to to the right source.

The only other option for that particle board repair would have been liquid epoxy. Again, it has to be really liquid and I do have some in stock. But I decided to use superglue as this is not as sensitive as fixing an instrument. The liquid epoxy that I have in stock is actually also a bit flexible when cured. Which is obviously a good property. Again, I do not wish to place commercial links, but if you google "liquid epoxy decayed wood repair" it should get to the right seller(s).

it is also important to make the right choice of wood glues for specific joints. Interestingly the only type of wood glue that we know has actually stood the test of time is hot hide glue (not to be confused with liquid hide glue). There's still furniture around that has been built during the time of ancient Egypt,held together by hot hide glue. But I used Titebond III.


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 Post subject: Re: Repair of a Badly Damaged (in shipping) Tefifon T574
PostPosted: Mar Fri 09, 2018 3:32 pm 
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Joined: Jan Sun 07, 2018 3:02 pm
Posts: 135
Now I have a technical question that falls outside of my area of technical experience.

Here is the schematic of the power supply.

Attachment:
t574-power-sup.jpg
t574-power-sup.jpg [ 81.13 KiB | Viewed 211 times ]

In red, I added what is not shown in the original schematic, but is present exactly as I drew it, in the actual radio. It is the connection to the cassette player AC motor and the position of the voltage selector switch as I currently have it.

I chose to place the voltage selector on 125V since I measured my mains voltage to be 120V. I have a a BK Precision DMM, Model 2707B, with true RMS.

So, the motor (rated at 220V, 50Hz) is connected to the primary taps of the transformer, as shown, and when the EZ80 tube is removed I measure about 214V on that tap. When the radio and motor are running, I measure about 208V.

The cassette player starts very slowly and needs a few seconds to get up to speed. At first it also needed assistance to get the freewheel turning,not not any more. Of course, I did a thorough clean/lube job on all moving parts.

The motion from the motor to the freewheel is transferred by friction and I do not detect any slipping.

So, I do not know how these players used to get into motion when they were new. Would they get up to speed faster than what I am observing? I do not know. I have not yet tested if the tape is playing at the correct speed.

Also, Do I worry about the voltage not being as high as what the motor is rated for?

Do I worry about there not being any isolation to the motor from the mains?

Thanks...


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 Post subject: Re: Repair of a Badly Damaged (in shipping) Tefifon T574
PostPosted: Mar Fri 09, 2018 11:44 pm 
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Joined: Mar Sun 01, 2009 10:27 pm
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Location: Ann Arbor, MI
You could briefly try it with the switch set to 110 volts. That would put more voltage on the motor and you could see if there is any difference.

If any of the bearings are of the type with microscopic passages for the oil to soak into, you sometimes have to soak them in oil for a day or so. Those tyoe of bearings tend to be a dull brass color. They give you the same impression as flat paint does.

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Tom


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 Post subject: Re: Repair of a Badly Damaged (in shipping) Tefifon T574
PostPosted: Mar Sat 10, 2018 7:00 am 
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Joined: Mar Thu 24, 2011 6:23 am
Posts: 338
Location: New Jersey
I would try connecting the motor to the 240 volt tap on the transformer primary.
I doubt that it was designed to come up to speed slowly. Since you haven’t tried a tape yet we don’t know if it has enough torqued to drive the tape or if the speed is correct.
You may have an issue with the frequency of the mains supply. Most AC motors will run slower with the lower frequency.

Please keep us posted.

Peace,
Rick


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 Post subject: Re: Repair of a Badly Damaged (in shipping) Tefifon T574
PostPosted: Mar Sat 10, 2018 2:53 pm 
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Joined: Nov Wed 14, 2007 11:37 pm
Posts: 1485
You did a wonderful job restoring this radio. Thanks for posting.!


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