• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

soft start and delay start - help please

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Joined 2013
When it says soft start for filament the heater voltage go from 0 to 12.6V and regulated in certain time. When you turn off and on the cycle will repeat. Timing is depended on charging of capacitor and must be discharged completely as soon as you turn off. Apart from regulation an NTC thermistor can be used power transformer, capacitor, prevented current inrush. NTC always depend on temperature and therefore the timing is not always repeatable if on/off too fast, NTC and capacitor are used soft start while capacitor timer control relay can give you longer time usually in 2 or more steps until full power is applied. Again you need to study the schematic to see if any pitfall and many are not "zero crossing" design when may not be used to turn on/off toroidal power transformer due high inrush current, to avoid it can only be safely turned on at AC mains zero crossing cycle.
 
No, no tubeamps with less then 1000V as B+ needs them. They are installed
for owners amusement only.

What is wanted is a turn-on delay or "flicker eleminator" where a short interruption
of power is dangerous. Either something that trips when power goes out, needing
a manual reset before power is restored, or a delay where power on is always
delayed more then 30s ( time needed for catodes to cool and caps to empty)
 
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Joined 2008
Paid Member
A soft start means that the voltage at the power supply output to the load circuit (in our case the audio circuit) goes from zero to steady state operating voltage at a rate that is retarded. A slowed ramp-up if you like. There are a number of reasons this might be be done, and there are a number of ways it can be implemented. It's usually done to protect components from undue stress at startup. For example, some circuits can draw a large amount of current at startup, blowing an otherwise sufficiently rated fuse. A softened start can be used to prevent this.

A delayed start on the other hand refers to having some kind of timing mechanism that puts a delay between the moment the power switch is turned on and the moment the power is seen at the power supply output to the load circuit. It doesn't imply a gradual increase, only that after switch-on, a certain amount of time has to pass before it is on. This too can be implemented by a number of different types of circuit.

The two can be implemented separately or together.
 
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