Modding a TV to use a thermistor for slow power on

[DavGoodlin]

I also agree that most tube failures do NOT involve open filaments. Some times a thermistor (G.E. CL60-5 amps or CL90-2 amps) is used to mitigate an upgrade that makes the power supply more efficient and robust.

RCA's CTC11 color chassis used a thermistor on AC line, later RCAs with automatic degaussing used a thermistor ahead of the rectifiers only.

Motorola also used a line thermistor "tube sentry" and may also have been accused of unsubstantiated claims of extending tube life.

On some HiFi consoles, a 3DG4 or 5U4 is used as full-wave rectifier but its heater consumes an additional 15 watts - 100% waste heat. The fact this tube needs to warm up along with others mitigates over-voltage during warm-up. If the tube were replaced by two silicon rectifiers (1N4007), B+ voltage may top 400 volts before settling down under load, stressing electrolytics unnecessarily. This is a good argument for using a thermistor, not so much for the tubes, which are tougher and replaceable.

On many of these console stereos, power transformers can be a delicate device capable of failure due to transient overloads or being inadvertently left on. To address that, add [email protected] ohm 10 watt resistors in series with AC line to drop 123 VAC to 117.