motorola tabletop tv currant inrush protection

[timmy]

what would be the best way to protect these 7 inch motorola sets from currant inrush? would the thermistor that is used for the degauss coil on rca sets work if its put in line of the ac in , either side of the ac in ? the one that is 120 ohms cold ?

[rca2000]

You need an NTC thermistor...one that stafrts at about 30 ohms COLD or so...and then drops to maybe 1 ohm or so...after it gets hot..

Deguassing thermistors are usually the OPPOSITE...they start LOW...and RISE to near an open ckt.

[decojoe67]

I actually made two junction points in two areas of my home with two older Variacs that I picked-up for next to nothing. Every radio and TV gets powered-up slowly to exactly 110V. What's also good is no set is ever left plugged-in that way too.

[bandersen]

The CL-90 works well. About 120 ohms cold and dropping to 3 ohms at 1 amp. It does get pretty hot in operation so mount it away from other components.

[timmy]

Originally Posted by bandersen

The CL-90 works well. About 120 ohms cold and dropping to 3 ohms at 1 amp. It does get pretty hot in operation so mount it away from other components.

So the degauss ones I have are 120 ohms cold so I'll need to see if they drop to low ohms, if not then I guess they won't work.

[Electronic M]

If it is a VT-71/TS-4 chassis variant and still uses the ballast, then that will provide inrush limiting.....If it has been replaced, then it should use the capacitor ballast replacement method to provide inrush limiting.....

[timmy]

Originally Posted by Electronic M

If it is a VT-71/TS-4 chassis variant and still uses the ballast, then that will provide inrush limiting.....If it has been replaced, then it should use the capacitor ballast replacement method to provide inrush limiting.....

the cap setup you refer to is the 250volt 10 uf poly caps to replace the 2 150 ohm string resistors, if I'm correct.

[Electronic M]

Originally Posted by timmy

the cap setup you refer to is the 250volt 10 uf poly caps to replace the 2 150 ohm string resistors, if I'm correct.

I believe so. I was able to get a GOOD glass ballast for mine off ebay some years back so I did not (have reason to) take much note of the specifics of the capacitor ballast substitute method when it was later devised....

[dieseljeep]

Originally Posted by Electronic M

If it is a VT-71/TS-4 chassis variant and still uses the ballast, then that will provide inrush limiting.....If it has been replaced, then it should use the capacitor ballast replacement method to provide inrush limiting.....

This one, we can agree on! The capacitor reactance is the best way to go.
Back in the day, the ballast tube or the resistance line cord was used because of the need for the radio to be for AC/DC use.
I know that the Motorola and other sets were for AC only, because of the voltage doubler. Also AC type caps were more expensive than the ballast tube arrangement and worked rather well.

[timmy]

Originally Posted by Electronic M

If it is a VT-71/TS-4 chassis variant and still uses the ballast, then that will provide inrush limiting.....If it has been replaced, then it should use the capacitor ballast replacement method to provide inrush limiting.....

The 250v 10uf poly caps for replacing the ballast resistors, 150 ohms, would any poly cap rated 250v 10uf be the same because I found caps with this rating on eBay and it is said in the auction that they are for audio systems. I would think they would be ok for using in the set to soften the currant rush, but all you pros would know better then me, lol.

[bandersen]

I added up the tube filament voltages, used 125 for the AC line voltage and came up with 8.2 uF rather than 10 uF.

Ideally, you would use a capacitor rated for continuous AC current like a motor run cap, but I've had good luck with basic polyester film caps like these from Panasonic. http://www.alliedelec.com/panasonic-...25kf/70260082/

[Kamakiri]

Originally Posted by Electronic M

If it is a VT-71/TS-4 chassis variant and still uses the ballast, then that will provide inrush limiting.....If it has been replaced, then it should use the capacitor ballast replacement method to provide inrush limiting.....

So if the ballast has been replaced with a solid state one, such as this:

http://www.videokarma.org/attachment...9&d=1290802806

Is an inrush limiter needed then? I have one that I made this ballast for and put in diodes to replace the seleniums, and when I powered it up, the 30 ohm 5w resistor started to smoke. Before I replaced the seleniums, it ran, but the sync lock in all directions was wonky and the picture was washed out.

[bandersen]

The capacitors act as inrush limiters, so, no, you don't need to add one.

[Kamakiri]

Good to know, so I have another issue that needs to be traced down this winter....thx!

[dieseljeep]

Originally Posted by bandersen

I added up the tube filament voltages, used 125 for the AC line voltage and came up with 8.2 uF rather than 10 uF.

Ideally, you would use a capacitor rated for continuous AC current like a motor run cap, but I've had good luck with basic polyester film caps like these from Panasonic. http://www.alliedelec.com/panasonic-...25kf/70260082/

I made up a few cap droppers, using scrap ceiling fan caps. They're rated at 250 VAC. You have to parallel them to get the proper value.