Stand By and Slow Heater Turnon

[Amptroll]

Hello, Strelok and Kevin,
   If the Fig.2-20 you are referencing to (I am not close to my TUT library) is the one that limits the AC voltage until the RC network charges and uses the IRFZ40 MOSFET; I can testify that this circuit works great.  As far as STD BY switches I have been using some of the methods of cathode STD BY switching discussed in TUT with great success also.  Again there is one that uses a MOSFET, 22uF eCap, 220k resistor, 10k resistor, 12V zener and a SPST switch which I have implemented with great success.  I try to stay away from mechanical switches with the voltages that are present in valve amps, because of the contact arcing deterioration of the contacts. 
Take care and peace always,
Rob


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.