17" RCA with a thermistor issue

[Chris K]

Chassis KCS126A. When I turn on the TV, the thermistor glows for a second or two along the disk edge...just in one pinpoint spot. Then it disappears. RCA part number is 107191 and it's 120 ohms cold. If I take it out and put in a 8 ohm resistor and always bring the TV up on a Variac, would I be hurting the set? The cold resistance on it now is around 8 ohms.

[dtvmcdonald]

If you always use a Variac, you don't need a resistor at all. Just put an AC voltmeter
on the 6.3 volt filament line and see what setting you need on the variac to get
6.3 volts when warmed up.

[zeno]

The most likely use is to ramp up voltage from a cold start.
On turn on the thermister starts at 120 ohms & quickly goes to near zero ohms.
This limits the surge of the PS electrolytic caps charging up.
Most sets use a @5.6 5Watt FUSE resistor for this.
Test is to jump it & bring up on variac.This is NOT a fix but lets you
check the set out BEFORE you chase & spend $$ on parts.
Thats probably what you have ( without seeing schematic ).

73 Zeno
LFOD !

[Chris K]

Originally Posted by zeno

The most likely use is to ramp up voltage from a cold start.
On turn on the thermister starts at 120 ohms & quickly goes to near zero ohms.
This limits the surge of the PS electrolytic caps charging up.
Most sets use a @5.6 5Watt FUSE resistor for this.
Test is to jump it & bring up on variac.This is NOT a fix but lets you
check the set out BEFORE you chase & spend $$ on parts.
Thats probably what you have ( without seeing schematic ).

73 Zeno
LFOD !

Thanks!!! I had a Zenith from the late 50s that used that same value resistor on the line. I'll try it

Chris

[N2IXK]

...

[Electronic M]

Based on the description it sounds like a standard modern CL-90 thermistor would sub... If you're ordering caps for it just add one or two to your cart on mouser or digikey, install it, and have a set you don't need to power up with a variac at the end of the resto. (I'd wait till the recap is done to install the thermistor).