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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Eli...how do I determine the primary current draw? posted by Audiodyssey on July 21, 2009 at 17:07:10:
The resistor type thing you described is a resistor/heater.
A surgistor is composed of two basic parts: a resistor/heater and a bi-metal strip that physically deflects when it's heated. The heater portion is wired in series with the load, usually the primary of the PT for old timey tube amps. The bi-metal strip is set up as a normally open switch parallelled across the heater and in close physical proximity to the heater. When current flows thru the heater it inherently limits max current inrush due to its resistance. It also gets quite warm which in turn heats up the bi-metal strip. As the strip warms up it begins to deflect towards the NO contact until it makes contact. At this point it shorts out the heater thus effectively removing it from the circuit. Since the electrical resistance of the bi-metal strip isn't zero, normal operating current flowing thru it generates enough heat to keep it deflected into the closed position.
About half the surgistors I encounter have failed heaters. They're usually open and look as though they were subjected to gross overcurrent...like someone replaced the fuse with a 15A unit so the surgistor became the defacto fuse. Messed up bi-metal strips are common too as are dirty contacts.
Although ingenious in concept, their Rube-Goldberg nature makes them problematic IMO.
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Follow Ups
- RE: Eli...how do I determine the primary current draw? - Steve O 07/21/0920:04:04 07/21/09 (0)
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