Hi, all.
Would - instead of implementing a soft start circuit - the habitual use of a Variac with slow manual ramp up of mains voltage to nominal
over f ex 30 seconds have any detrimental effects on the tubes of a tube power amplifier ?
thank you,
FrankieS
Would - instead of implementing a soft start circuit - the habitual use of a Variac with slow manual ramp up of mains voltage to nominal
over f ex 30 seconds have any detrimental effects on the tubes of a tube power amplifier ?
thank you,
FrankieS
Valves do not like low heater voltage!
If it worries you that much, use a PTC in series with the HT supply but that in itself, may cause problems.
If it worries you that much, use a PTC in series with the HT supply but that in itself, may cause problems.
Tubes in general has no problems with direct applying of power. Complicating power on sequence has in itself negative impact on reliability.
OK, how about if you can't get a lamp current limiter?
Our legislature long ago made incandescent lightbulbs illegal in the state. So I can't get a 40w or 70w lamp... Other than driving to Nevada or Arizona, what are my other options?
EDIT: looks like we can still get incandescent appliance lamps at 40w.
Our legislature long ago made incandescent lightbulbs illegal in the state. So I can't get a 40w or 70w lamp... Other than driving to Nevada or Arizona, what are my other options?
EDIT: looks like we can still get incandescent appliance lamps at 40w.
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I guess it all depends on what the soft start was really being used for. Tube circuits (once working correctly) have no need of a soft start to prevent surges, although delayed HT can be valuable in some cases if supervisory circuits NEED to come up first. Hungry capacitors at start up are far less of a problem with tube circuits than solid state. Even a cap input filter isn’t a problem with the usual circuit values. Even with crazy amounts of capacitance the typically high HT winding resistance will limit the current spike from that at start up. So the only real need for a soft-start circuit is momentary core saturation from the decaying DC component in the primary at start up. With a big enough transformer that does get ugly. A PTC disk can be used, although I don’t see any harm in using a variac. No need for it to take 30 seconds though. The time it takes for you to turn the dial to 120V is long enough. That’s slow enough of a ramp up not to put any DC into the core, and fast enough not to stress the heaters.