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AC Current Limiter?


It is simply a 120vac soft start home brew, resistor and relay, resistor limits the amount of voltage on initial turn on of the amplifier allowing the electrolytic caps to charge up a small percentage, then the relay becomes enabled and the full 120vac is applied to the power supply of the amplifier.

It works, Google soft start, many sites show how to build one and describe the purpose.

The Heath kit SB-1000 sounds like someone kicking the wall when it is turned on, after installing a soft start it is nice and quiet.

A soft start can be built for a third of the price of that auction.
 
Not necessarily a gimmic depending how it is built. If it simply has resistors in it then it is a piece of crap. If it has thermistors then it is not so bad. CRT type televisions have had them for decades. The thermistors drop the voltage during a current surge when first turned on because they heat up rapidly due to current draw and as the current settles down they drop to near zero resistance. The best way however is by using a relay and a couple resistors that are switched in/out of the primary leads. I doubt the device shown uses relays. All in all it does work but how well depends on what is inside.
 
Ameritron has sold them for several years. I believe the AL1500 and 1200 have them built in. In rush protection from Ameriteon looks like a single outlet extension cord you plug your amp into.
 
It is not a gimic it is in-rush limiting device. You normally build it as a separate card and install it in the amplifier. This is designed for those that are not up to buying a card installing the components themselves and then putting inside their amplifier.

In this case you would plug this device into your power-supply then plug your amplifier into it.

In a tube amp you have all kinds of capacitors int he power supply area and when you turn it in on it is like a tsunami their is this huge amount of empty power hungry space in the cap's and they want to be feed. So current can rush in at a rate that exceeds the supply capacity of the transformer and the wiring and other parts along that path. It would be like using a fire house to get a sip of water. By limiting how quickly the voltage and current can rise feeding your high voltage power transformer you effectively prevent the massive spike. It is like slowly turning on a facet in your kitchen versus punching a hole in a water main!

You could build the unit so that spikes do not really do any harm but it is more cost effective to just limit the in-rush current then it is to use insanely beefy components just to deal with in-rush current.

You might have seen some specifications on tubes where the tube can disapate 350 watts modulated continuous or 10,000 watt's in a pulse. The problem here is that all the other parts need to be able to take that and few of them can. If you are building a 350 watt amateur tube amp you do not chose resistors,caps, diodes, and a transformer based on the idea that you are going to pulse that unit at 10,000 watt's of output in digital modes with encrypted data in pulses if you tried to do that you would kill the amplifier in a hurry. Well when you first turn it on it is creating a situation that is not unlike the digital mode 10,000 watt pulses over time every time you do that it damages the parts a little bit until final you have killed you amp in say 100 hours of operation that should have gone for at least 1000 hours of operation with out fail. It can melt insulation in a hurry and if you are talking about a $480 transformer that is a lot of money to toss out the window if it could of been prevented with an in-rush current limiting board.

My analogies are not accurate of what is going on I know this and I grossly over simplified things I know.Trying to paint a picture not be scientifically accurate for the record.
 

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