NTC Thermistors and inrush current

[Ears]

Has anyone any experience using these devices for inrush current suppression?

If they are useful, then where is best to use them? (I.E. Before the PT primary or in various PT secondary locations such as in heater lines or between secondary and HT rectifier or post the rectifier.)

Are there any cookbook rules for choosing the correct values? are there recommended suppliers with good range of components suitable for tube amp purposes?

Yeah I know, that's a lot of questions, but these devices on face value seem to be a godsend, so there must be a catch.

[VacuumVoodoo]

http://www.wizard-labs.com/

Read the "Safety & Reliability" in the Technical section. There's also an excel sheet that helps you find proper NTC. Link to the xls sheet is in the text so you need to read this stuff till you stumble on it.

[Andy Le Blanc]

I once saw a good article and project in glassaudio or audioexpress about that... very practical

[Ears]

Thanks guys, it's a cool spreadsheet, any idea how the X and Y terms in the equation can be deduced from the device data sheets?

[David Root]

NTC thermistors can be useful on the live (black wire) side of a toroidal power xfmr. Toroids have higher inrush currents than EI designs of the same rating.

I put one in my last amp which uses a toroid PT and OT.

In an EI PT I wouldn't worry about it unless you're deliberately abusing it currentwise. In that case it will save on mains fuses bigtime!

[Allynmey]

They would be cool for using >60uF with a GZ34.

[David Root]

You know that is a real good inference! Have you tried it?

[Andy Le Blanc]

In Glass Audio Vol. 12 #6 2000 theres a short little piece called "The Power Line interface" by Pete Millett..... theres a schematic that uses a Keystone Carbon CL-110 as a inrush limiter right on the back of the power switch....in conjuction with a MOV. very simple application....