Wirewound resistor - Printable Version
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+--- Thread: Wirewound resistor (/showthread.php?tid=11203)
Wirewound resistor - standardtwin - 12-18-2014
I'm working on a Delco 32 volt 4049 farm radio. I've successfully repaired the power supply (vibrator) and have slowly worked my through the chassis replacing all caps. The vibrator gets the voltage up to around 100 v in the chassis.
I actually got it to receive a station for a short period of time, sounded like it was underwater, then slowly came in and sounded OK before I lost it, and still have no reception again as of yet. The Audio output is OK, and all tubes are good, with all filaments up. It uses 2 78's, a 75, a 35, a 6B7 and a 43 output. The 78's and 6B7 are NOS. THe chassis was rusty, so cleaned it up, polished the sockets and shields. Any thoughts or suggestions would be helpful.
The issue I ran into is a broken wirewound resistor from fumbling fingers. It is very fragile, looks like a red cloth wire, but is actually fine wound wire like a long spring. I had to look this up to figure out what it was. I had no experience with it before. It is a 275 Ohm unit in the B+ from the RF 78 tube at 3 volts. If I did the calculation right, I get .14 watt, as its 2X3VX3V/125V
I can find so far a 270Ohm 1/4 watt.. Would this work correctly?
I am a newbie, and have so far done OK, my first fix being a 42-380. THanks for your patience!!
Mike
RE: Wirewound resistor - morzh - 12-18-2014
I am not sure what 2x3x3/125 is....3 V over 275 ohm is 9/275=0.033 W
Yes 270 ohm, will work.
RE: Wirewound resistor - standardtwin - 12-18-2014
Thank you for that.
The formula was posted on another site. Wattage= 2X "x" volts X "x" volts / voltage on the cathode.
Perhaps there is a mistake there. In any case I appreciate the answer.
Anyone have thoughts on non reception?. I had it somewhat before I replaced the caps that were on the 78RF and the 4500 ohm resistor. I had to replace the original resistor as the wire broke off it flush when manipulating it.
The output side is OK, its picking up the static from the vibrator, and the volume and tone both work, and did when it had a station. I have literally replaced all caps and electrolytics in the chassis AND vibrator power supply, with the exception of a resistor cap combo, R6/C6.. I think it is off of the 37 oscillator tube. It must be something simple, and just need to figure out where to focus on. I hate to give up, as it did work albeit for 5 min or so. I got video to prove it
Thanks!!
RE: Wirewound resistor - morzh - 12-19-2014
If you know the voltage across the resistor, the power is ALWAYS "V*V/R".
If you know the current - "I*I*R"