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Technics SA-700 Thermistor

mustang1102

mustang1102

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I need the following part for a Technics SA-700 Receiver:

TH602 RRT251 Thermistor, Driver Amplifier Circuit

How do I go about deciphering what size for value to purchase......does the RTT251 part number give any indication as to which one is required...? Any help is appreciated. Below is a snapshot of the power amp board section that contains the thermistor.

Thanks.

technics sa-700.jpg
 
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Is TH601 still good? Same part number? If good and the same remove it, measure the resistance at room temp. and then heat it up and measure again, that should give some clue to what you are looking for.

Craig
 
thermistors have whats called a beta curve. Need to know the temperature and resistance at two points, and it can be calculated from there.

NTC thermistor calculator | Lasercalculator

there is probably some involved math that uses a bunch of funny symbols but plugging in the numbers is easier.

once you have those numbers you can pick something based on the beta and resistance. I think the listed resistance value is at 25C / 77F but not 100% on that one.

I very recently learned about this when researching a suitable part for an interior temperature sensor in one of my cars.
 
All right folks, not sure what to do here now.

To answer the question from @ llwhtt , yes TH601 was good. When removed from the circuit and measured laying on the bench, I got about 300 ohms. As I heated it up, the resistance dropped steadily, and I stopped heating it when it hit about 100 ohms, I think it just would have kept on going.
I guess I was thinking the resistance should have been increasing instead of decreasing as it heated up....?

So, not sure what that tells me, or how to plug that info into the calculator from @gadget73. What do you think ?? Does this yield any help in deciding a suitable replacement.....?? :dunno:
 
I'd leave it alone unless you know it's off value then.

To plug in the data, the easier way would be to do something like take a glass of ice water with a thermometer in it. Stick the thermistor in there with it hooked to an ohm meter. Note temp and resistance. Same with some hot water. Plug in the values and that will get you the beta curve.
 
mustang1102 said:
All right folks, not sure what to do here now.

To answer the question from @ llwhtt , yes TH601 was good. When removed from the circuit and measured laying on the bench, I got about 300 ohms. As I heated it up, the resistance dropped steadily, and I stopped heating it when it hit about 100 ohms, I think it just would have kept on going.
I guess I was thinking the resistance should have been increasing instead of decreasing as it heated up....?

So, not sure what that tells me, or how to plug that info into the calculator from @gadget73. What do you think ?? Does this yield any help in deciding a suitable replacement.....?? :dunno:
Click to expand...
If it's still good then why do you want to replace it?
 
There are two, one in each channel. TH602 measures open. I removed the other good one to take measurements to see if I could figure out what kind of replacement would be best.
 
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