[R-1051] Oven Bridge Resistor

[Dennis McLaughlin]

On 03/27/2012 08:45 AM, Steve Hobensack wrote:
> I am trying to repair the oven bridge resistor mounted on the underside of the oven on the frequency standard module. I removed the plastic foam with a drimmel wheel. The resistor is cooked, and split open. It is a wire wound resistor using extremely fine wire. Is this resistor a thermistor? What is the cold resistance? I cannot measure because the fine wire is destroyed. This resistance can be found by pulling the crystal board from  the oven . There is a 5 prong connector at the bottom of the oven cavity. Pin 5 is 5 MHz output, 4 is 28vdc, 2 is the top end of the oven heater wire. The bridge resistor is between prong 3 (middle) and chassis ground pin 1.
> Thanks
> Steve N8YE 		 	   		
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Steve,

It is a positive temperature coefficient resistor.  From my notes,

PRC
PT094
3900 +/- 1%
TC.45%

Made by
PRECISION RESISTOR CO., INC.
10601 75th Street North, Largo, FL 33777-1421 U.S.A.
Tel: 727-541-5771 Fax: 727-546-9515
E-mail: prc at precisionresistor.com
Web Site: http://www.precisionresistor.com

Most thermistors are a negative temperature coefficient.  I tried to get 
a 10k ohm one to work by reversing the bridge output to the amplifier, 
but had no luck.

Also check the transistor in the bottom of the can.  I have some that 
the gold plated leads of the transistor have corroded off at the body of 
the transistor.  Something in that putty like stuff might of done it 
over the years of operating at 75C.

Dennis McLaughlin