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 Post subject: Realistic DX-160 thermistor question..
PostPosted: Mar Sat 03, 2018 11:09 pm 

Joined: Dec Tue 08, 2015 12:53 am
Posts: 414
Location: shirley NY...Long Island
Hi all....I got my new(NEW TO ME) DX-160 radio today...I took a chance and bought one on..u know where bay, and the description said no audio on any band...Well knowing a little about this radio, it could have been a few things, and since the lights lite could be the fuse, and I would have to figure out why it blew...or other things in the circuit. Bear in mind I had NO IDEA even if this radio had any circuit boards in it...what a relief it was to fist see the BC bands ferrite bar....then, seeing the two circuit board intact...

ANYWAY...on to my question....on SSB, and CW and using the BFO and band-spread tuner SSB and CW sounded very thermistor in question is the one, that is between two germanium diodes on the left side, of the left circuit board...IF you change that temp even the slightest bit it changes the tuning, so my question is...if you get the radio to operating temps...and let it sit in the environment that it will be in ....can you not remove that thermistor and check the resistance, and replace it with the said resistance, with a carbon resistor...will the drift problem be GONE?????

If not, I guess I do not understand why it is in the circuit to begin with..

Kenny KE4HVE

 Post subject: Re: Realistic DX-160 thermistor question..
PostPosted: Mar Sun 04, 2018 12:22 am 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5894
Thermistors are designed to vary their resistance to compensate for the drift in another component's value due to a change in temperature. If you directly heat the thermistor then it will create drift because you are exposing it and the compensated component to different temperature. The compensation isn't perfect but the designer felt that without the thermistor the value change would have been too great.

If you have excessive drift (be sure and compare to another DX-160 and not a higher end communications receiver) then it probably isn't the thermistor at fault but another component that has strayed out of tolerance. Depending upon the thermistor you may find specs that will allow you to chart its resistance vs temperature to determine if there is a problem but generally these are pretty reliable components.

The biggest cause of abnormal (beyond design) drift in most vintage receivers is a main or bandspread variable capacitor where the rotor to stator plate spacing is no longer equal. With better capacitors this can be adjusted via the thrust bearing; if the spacing isn't equal the capacitance vs temperature changes increases significantly.

Rodger WQ9E

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