Some glass encapsulated thermistors I salvaged from some scrap telephone
equipment - I was hoping were RA53 as sometimes used to stabilise the
amplitude of simple AG signal generators.

Having found the data sheet online, I find that the RA53 has a room temp
res' of 5k - the one's I have are nearer 200k, so they might be RA25.

Anyone know where to look for info that might help in re designing such
circuits to accommodate the higher resistance thermistor?

TIA.

ian field wrote:

Some glass encapsulated thermistors I salvaged from some scrap telephone
equipment - I was hoping were RA53 as sometimes used to stabilise the
amplitude of simple AG signal generators.

Having found the data sheet online, I find that the RA53 has a room temp
res' of 5k - the one's I have are nearer 200k, so they might be RA25.

Anyone know where to look for info that might help in re designing such
circuits to accommodate the higher resistance thermistor?

The thermistor's in the feedback loop, so you'd have to scale the associated
values.

Graham

"ian field" wrote in message
...
Some glass encapsulated thermistors I salvaged from some scrap telephone
equipment - I was hoping were RA53 as sometimes used to stabilise the
amplitude of simple AG signal generators.

Having found the data sheet online, I find that the RA53 has a room temp
res' of 5k - the one's I have are nearer 200k, so they might be RA25.

Anyone know where to look for info that might help in re designing such
circuits to accommodate the higher resistance thermistor?

TIA.



I've been down the same path with those nice telecomms thermistors but they
only start usefully dropping their resistance in oscillators running maybe
50Vrms. (They've got to see the high voltage just to dissipate a little
power in the high resistance bead, hence giving some useable resistance
change).

The 5kohm RA53 was perfect for the job but haven't seen 'em for the past 10
years. I now use 'DF08', DIL package, 1Amp bridge rectifiers. The diodes are
very well balanced, allowing clean sine generation.

"john jardine"

Having found the data sheet online, I find that the RA53 has a room temp
res' of 5k - the one's I have are nearer 200k, so they might be RA25.

Anyone know where to look for info that might help in re designing such
circuits to accommodate the higher resistance thermistor?

I've been down the same path with those nice telecomms thermistors but
they
only start usefully dropping their resistance in oscillators running maybe
50Vrms.

** The RA53 has a maximum voltage around 4 volts rms to stay within the
rated power.

http://www.thermometrics.com/assets/images/ra.pdf

( there is an obvious typo in the data for the RA 54 )


(They've got to see the high voltage just to dissipate a little
power in the high resistance bead, hence giving some useable resistance
change).


** The RA series thermistors requite only 1 or 2 mW to operate properly in
an audio oscillator.

The 5kohm RA53 was perfect for the job

** As was the RA 54.

but haven't seen 'em for the past 10 years.

** Ditto.


I now use 'DF08', DIL package, 1Amp bridge rectifiers. The diodes are
very well balanced, allowing clean sine generation.


** ????????????

Diode stabilisation generates lotsa odd order harmonics.



..... Phil

"Phil Allison"

Correction:

** The RA53 has a maximum voltage around 4 volts rms to stay within the
rated power - as does the RA25.

http://www.thermometrics.com/assets/images/ra.pdf

( there is an obvious typo in the data for the RA 54 )



........ Phil