Temperature Controllers for QRSS Part 3

Here is info on another temperature controller used by PA0TAB which uses discreet components mounted at the crystal.  I'll quote the email:

"Hi Bill
I use another oven. Very simple. article Elektron 1976-6
See attachments. The picture is one of my versions
I feed from 12V stab and at the picture a 2N2905 is the PNP
I used 2 composite carbon resistors (Allen Bradley)
because they have flat surface. I use tin plate as mounting.
I soldered the Xtal, the 2905  and one contact of the NTC direct to the tin plate.
So they have a good thermal contact.
For 12v you have to increase the feeding resistor to the NTC thermistor.

I have also a version with one heating resistor of 4w 82 ohm ceramic
and a BD136 PNP (TO126 housing) also soldered
I use a styrophor isolation

I uxe an electronic thermometer and a mA meter to adjust.
Then I relace the potmeter by a fixed resistor
Temperature is adjustable about 90 til 130 degr F I use 110 degr.F.
I measure the temp amd the current. When the current goes down and the temp is to low decrease the potmeter til you have the right temperature.
Wait half an hour and check temp. If it is ok you could replace the potmeter by an equal resistor."

73 Johan pa0tab

Temperature Controller Used at PA0TAB

I recognize the two transistors as a Darlington pair and that makes me think of the op amp circuit I use (Part 1) but without the op amp...and why not.

Thanks for sharing, Johan.

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