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 Post subject:
PostPosted: Jul Sun 27, 2008 3:58 am 
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Joined: Jul Wed 09, 2008 1:40 am
Posts: 345
Location: Orlando, FL
Thanks for the scans Phil. It is now starting to make sense. Bought the diodes and some terminal strips today and started to install them. My question now is how do I determine which way to orient the electrolytics. On my other schematic it had a +/- to tell me how they go in. This one doesn't seem to show that. Clarify for me please!

-Shane-


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 Post subject:
PostPosted: Jul Sun 27, 2008 9:48 am 
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Joined: May Sun 25, 2008 6:49 am
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Location: San Pedro, Ca. 90732
I have a question. Is the wire that is used inside the ballast iron or ni-chrome. Fred.


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PostPosted: Jul Sun 27, 2008 3:20 pm 
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Location: Manitowoc, WI USA
You'll notice the symbol for a capacitor has one straight line and one curved line. The straight line is positive (+) and the curved is negative (-). Hope this helps you.

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 Post subject:
PostPosted: Jul Sun 27, 2008 5:58 pm 
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Location: Orlando, FL
I figured that had something to do with it. Thanks Phil.
-Shane-


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 Post subject:
PostPosted: Aug Sat 02, 2008 2:27 am 
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Joined: Jul Wed 09, 2008 1:40 am
Posts: 345
Location: Orlando, FL
I thought it was time for an update.
I have all the paper and wax caps replaced.
Diodes and terminal strips are installed.
So that is good.
The bad: The electrolytics were half way done when I realized I had installed some of them wrong. I was reading the schematic and soldering pin to pin of the tubes instead of from point to point in the circuit that they fall into. (dumb...I know)
As of right now after checking I believe that C90 140mfd,C54A 20mfd, C54B 100mfd,and C39B 120mfd are all correct. So that leaves 3 others to figure out.
One of my big questions right now is with the electrolytic cans...if there is no symbol around a terminal and it is sort of farther from the central terminals with symbols, is it a ground and can whatever is attached to them be left in place?

Thanks for the help guys,
-Shane-


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 Post subject:
PostPosted: Aug Sat 02, 2008 6:25 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 846
Location: Crystal Bay, NV
Yes, the smaller flat lugs located nearer the outer edge of the can are the negative connection, and connected to the outside of the electrolytic can.

Note that some of the electrolytic cans in the Motorola set have the negative can connection connected to about 120 volts, not the chassis ground. The cans are "hot". When electrolytics are mounted with an insultator, this is reason why. Motorola put paper sleeves around these cans, but they may have been lost. In any case, handle with care when the set is plugged in.
=====
Ron


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 Post subject:
PostPosted: Aug Sun 03, 2008 1:35 am 
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Joined: Jul Wed 09, 2008 1:40 am
Posts: 345
Location: Orlando, FL
Ok, I'll look into that. I'm just trying to figure out which connections I can leave to the cans (AKA Chassis ground) and which ones need to be mounted on the terminal strips.
I'm close, real close!
-Shane-


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 Post subject:
PostPosted: Aug Fri 08, 2008 4:14 am 
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Joined: Jul Wed 09, 2008 1:40 am
Posts: 345
Location: Orlando, FL
Time for an update. I basically retraced all my steps and corrected my mistakes (I wasn't that far off). I left all the grounds in place as they were after looking at the grounding system more thoroughly and figuring out that all the cans had spacers separating them from the chassis ground (they all ground to each other and then through a cap to the chassis.). I still need to go buy/replace the 120mfd electrolytic and then I can power it up. I am building a dim bulb rig in the meantime.

Cheers,
-Shane-


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Feb Mon 15, 2021 1:04 am 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 887
Location: east canton ohio 44730
oh dang it and the thread goes dead?? 7vt5a here. Anyone know if he finished it??? Great reading for me though.


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 Post subject: REVIVED: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Thu 02, 2021 1:10 am 
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Joined: Jul Wed 09, 2008 1:40 am
Posts: 345
Location: Orlando, FL
So after many years I'm reviving the thread. The answer is no, I didn't finish it. I gave up on it after many attempts to fix and it got left in the closet and later the garage. I moved on to AA5s as others suggested for learning purposes and expanded to SW sets. I've gone through about 20-30 radios at this point with a lot of success. Always learning something new along the way. I eventually tried a TV again, a Teletone TV-149 and was successful. Later on I picked up a 1948 Admiral that had a couple issues and got it working once again. There is a Pilot TV37 sitting in the cue patiently waiting its turn as well. I recently decided to start clearing out some of the ratty and uninteresting sets that I had. This was one of them until last night. I started looking at the underside of the chassis again again and said well maybe I've learned enough to get it back on track. I retraced all the un-terminated wires in the power supply section against the schematic and labeled them accordingly. I think where I got twisted up last time was the difference between the chassis and the floating grounds referenced in the schematic. Its hard to tell as I recycled the lytics into something else awhile back and I can't tell if I had them connected to chassis ground or floating. I know the difference know and how to read it. I also discovered since that I incorrectly thought that pin 5 on the ballast fed the other three sections of the ballast. Turns out my schematic is hard to read and it's pin 6! I verified this comparing the part numbers, to diagrams of the ballasts, to my schematic, and then the TV. It all lines up. I'm ordering the caps today as well as components to build the capacitor type ballast discussed here:

https://antiqueradios.com/forums/viewtopic.php?f=3&t=320262

Anyways, hopefully I learned enough in the past 13 or so years to be successful this time. The case is a little ratty now but still worth bringing back in my opinion. Wish me luck.
-Shane-


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Wed 22, 2021 7:12 pm 
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Joined: Aug Fri 14, 2015 10:30 pm
Posts: 46
Location: Henderson, NV
I found this schematic for the Motorola ballast replacement on this forum years ago. I can say it works well. Note the part number it replaces.


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Motorola BallastReplacement2.jpg
Motorola BallastReplacement2.jpg [ 43.89 KiB | Viewed 222 times ]
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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Thu 23, 2021 12:10 am 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 887
Location: east canton ohio 44730
so for pin 2 is 10uf and pin 7 is a 10uf?


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Thu 23, 2021 2:10 am 
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Joined: May Fri 29, 2009 4:35 am
Posts: 2264
Location: Chicago, IL USA
Yes, although 8.2 uF works better. Also a good idea to use AC rated motor run capacitors like for ceiling fans.


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Thu 23, 2021 4:06 am 
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Joined: May Sun 17, 2009 10:08 pm
Posts: 375
Location: Massachusets, 02019
They do have a glass version ballast


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Mon 27, 2021 10:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2902
Location: Olympia WA USA
If you chose to repair the ballast with "brass crimps" you should use the special high temperature ones used in appliance service for stoves, dryer heaters, etc.

My own experience in trying to get a "standard" brass crimp or splice to hold up have been dismal until I found out about the hi-temp ones. No failures after that.

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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Mon 27, 2021 10:55 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 887
Location: east canton ohio 44730
tvdude211 wrote:
They do have a glass version ballast


number of glass version ballast?


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 Post subject: Re: Motorola 7VT5R Se Rectifier/Ballast Replacement
PostPosted: Sep Tue 28, 2021 2:56 am 
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Joined: May Fri 29, 2009 4:35 am
Posts: 2264
Location: Chicago, IL USA
It's the same as the Motorola part #. Amperite 17A485459

Here are four version. Left to right.
Clarostat replacement, JFD OEM, Amperite replacement and homebrew using a thermistor, capacitors and resistors.
Image


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