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I keep burning them out.
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have a resistance rating and a current rating, IIRC. The idea is that the thermister slows the current inrush just enough to avoid damaging things like the capacitors or the tube heater elements. Too large a resistance and the additional strain on the device can cause it to blow.
Stu
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The initial resistance, if too high, may cause the device to eventually fail. Too low, of course, means that the initial current inrush may be a bit too high for real safety.
The same holds true for fuses. Quicksilver used to use 3.125 amp slow blow fuses, but as they are increasingly harder to source and getting more expensive, they switched to the common 3 amp fuses. They do have a tendency to blow after a certain number of on/off cycles. This may be occurring with the value of the thermister you use.
It is also interesting to note that modern slow blow fuses are not built to withstand a higher inrush current as the older models. The modern fuses have a simple coil of wire around a fiberglass core. The older models are spring loaded with a much more robust fusible link( they actually sound better, BTW). The problem is, while they are still made, the cost is now about $5 a piece and very few brick and mortar supply houses carry them for that reason.
Stu
I might add that I alone seem to be having this problem. All that I know that is different is that I constantly have 122 volts But I do know people with very similar voltages, such as 120 volts who have had no such problem.
I have installed them in a few of my components as in-rush current limiters.
The tube preamp and power amps have them and I like the way the power lamps 'come up to full brightness' indicating to me the power supply and the associated capacitors did not get hit with a current surge on turn-on.
I used to use an amp that had thermistors to limit current on start up. The only time I had them pop on me was when the unit powered off and then back on too soon - - in this case, the thermistor is still warmed up, and it doesn't limit the current well, so too much hits it and fries it.
This happened to me once when I had switched the amp off, changed cables and switched it back on. Poof! A lasting lesson. The only other times were when our neighborhood experienced brief power disruptions. PITA, to say the least.
to see if the amp has a temperature.
I think its more odd you keep "burning them out". As you probably know a thermistor is put in circuits to protect them. It could have to do with this:
""NTC thermistors can be used as inrush-current limiting devices in power supply circuits. They present a higher resistance initially which prevents large currents from flowing at turn-on, and then heat up and become much lower resistance to allow higher current flow during normal operation. These thermistors are usually much larger than measuring type thermistors, and are purposely designed for this application.""
I mean as to the use of it. I have no idea why they keep failing for you.
ET
Are they rated that way or by resistance?
I'm sorry but I really couldn't say what the problem is. I would most likely trust the companies engineering but that of course could be off. Is the amp an older design that's been available for some time and is time tested or is it new and perhaps not? Have you contacted the company regarding the problem? If nobody is having the problem but you your environment could be the issue. When it goes does it happen when you turn on the amp or when its been playing a while and has gotten warm/hot?
There are just too many factors involved, sorry. Not that I could provide a solution even if I knew all those factors. Here is a selection of a few at the link below for numerical comparison.
ET
That is what I wanted to know.
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