Heater voltages - Videokarma.org TV - Video

timmy · #1 12-23-2025, 05:12 PM

I once read an article that stated that heater voltages should be what is listed for a specific tube if to high or to low damages or lowers the life of the tube ok it makes sense so with a 7jp4 at 6.3v is good but I find that most of the Motorola vt71 sets the heater voltage runs kind of high at least mine do 6.8-7.2v how can I get these voltages down where they should be. There is a resistor in the string that the crt is part of and all these resistors are what is listed in the schematics so these voltages should be where they supposed to be. I think these elevated voltages will prematurely ruin the 7jp4. I don’t know but maybe Motorola designed them to run the heater higher then it really should.

old_coot88 · #2 12-23-2025, 05:43 PM

If every heater in the string is running high by the same amount, you may have high line voltage. Have you checked it? If it's high, you could increase the value of that series resistor.

timmy · #3 12-23-2025, 05:58 PM

Quote:

Originally Posted by old_coot88

If every heater in the string is running high by the same amount, you may have high line voltage. Have you checked it? If it's high, you could increase the value of that series resistor.

That will be next to check line voltage although I don’t think it’s high. I wonder if the series resistor I used in these sets for the crt string if the wattage is to high I don’t know if this would make any difference. If there is a 10 watt I may have used a 25 watt

old_coot88 · #4 12-23-2025, 08:32 PM

The wattage-rating isn't the criterion. What's its actual ohms value?
OOPs, sorry Bob. Missed your posting.

bandersen · #5 12-23-2025, 08:27 PM

I made a video where I analyze the ballast and do the math. The ballast resistance is not high enough even for 117 vac line voltage.

Also the tube lineup did change over time, but for the most common TS-4J or TS-18, the two strings are not equal.

They should be about 130 and 150 ohms.
https://youtu.be/vuYYx8AXbFc?si=oAIt7oyLNbKI20Wj&t=3751

bandersen · #6 12-23-2025, 09:30 PM

Motorola shows only 105 ohms in the schematic. Not sure what Timmy used.

timmy · #7 12-24-2025, 05:10 AM

I since moved to another location and the voltage has been good however the last location the voltage has been up around 124v so I should check the heater voltages on these tvs now that I’m in a different place now. Here’s what is in these sets, 105-150 20watt 37-50 10watt 22-25 20 watt 200-200 20 watt