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05-30-2020, 03:01 PM
Hi Strelok
The TUT method for heater surge protection (Fig.2-18) is universal and easy to adjust for whatever the heater load is just by changing the limit resistor value. One relay control circuit is shown in Fig.2-19, and can be any type of timer circuit you wish to deploy. Fig.2-20 shows an idea from Wireless World that provides reduced net voltage output over a set time constant, but does not provide specific current limiting you can set.
Figs. 3-18, 3-19 of POP have active current limiting that requires some excess voltage be available, which is often the case for DC heaters. Same with TUT2 Fig.2-74.
Limiting the heater turn-on surge will increase tube life, but remember that if a tube is not mechanically upset, it will generally last beyond fifty years even without such measures.
The TUT method for heater surge protection (Fig.2-18) is universal and easy to adjust for whatever the heater load is just by changing the limit resistor value. One relay control circuit is shown in Fig.2-19, and can be any type of timer circuit you wish to deploy. Fig.2-20 shows an idea from Wireless World that provides reduced net voltage output over a set time constant, but does not provide specific current limiting you can set.
Figs. 3-18, 3-19 of POP have active current limiting that requires some excess voltage be available, which is often the case for DC heaters. Same with TUT2 Fig.2-74.
Limiting the heater turn-on surge will increase tube life, but remember that if a tube is not mechanically upset, it will generally last beyond fifty years even without such measures.
