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Ballast / Resistive line cord replacement/substitution

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Ballast / Resistive line cord replacement/substitution Empty Ballast / Resistive line cord replacement/substitution

Post by LarryC on Sat Feb 21, 2009 2:14 pm

Hi Everyone,
I want to start this topic as a means of having the info available for when ARF is down.
So, if everyone who has posted info on ARF related to this topic would be so generous as to post it here , it would be greatly appreciated. I know there was a wealth of information posted at ARF on the various methods people have come up with. Very Happy
LarryC
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Post by RadioRich on Sun Feb 22, 2009 2:46 am

Hello Larry,
Well Peter was the brains behind that posting on ARF he talked about using a cap instead of a resistor to drop the voltaged so the set would work without that resistor line cord or know as curtain burner . also there is the use of a diode to .
Sincerely Rich

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Ballast / Resistive line cord replacement/substitution Empty RTMA color code for line-cord resistors

Post by Resistance is Futile on Sun Feb 22, 2009 3:47 am

This is from MARKUS TELEVISION & RADIO REPAIRING

"With color-coded line cord resistors, the insulation on the two regular line-cord wires is either red and blue or red and black. The insulation on the resistance wire is colored according to the resistance value in the line cord as follows:
Yellow.............135 OHMS
Blue................160 OHMS
White..............180 OHMS
Green..............200 OHMS
Light Brown.....220 OHMS
Orange............260 OHMS
Gray................290 OHMS
Maroon............315-320 OHMS
Dark Brown.....350-360 OHMS

Figuring a line cord resistor value. The simplest way to finding the resistance value of an uncoded line cord resistor is to look on the circuit diagram of the set. The resistor value in ohms will be shown next to the line-cord plug.
If the circuit diagram is not available, the resistance of the resistor can still be found. Add up the filament voltages of all the tubes in the set and subtract the total from 117volts(the power-line voltage), to get the voltage that must be dropped by the line cord resistor. Multiplying this voltage value by 3.3 gives the required resistance in Ohms. (This assumes the the set is of standard design, using tubes drawing 0.3 ampere heater current.)
As an example, take a radio using a 6A8, 6K7, 6Q7, 25A6, and 25Z6.
Looking up the filament value of each tube in turn in a tube handbook, shows the individual filament voltages are 6.3, 6.3, 6.3, 25, and 25 volts respectively. Adding these gives about 69 volts as the total required filament voltage for the set.
Subtracting 69 from 117 gives 48 volts to be dropped by the line cord resistor. Multiplying 48 by 3.3 gives 158.4 ohms as the resistance of the line-cord resistor, and therefore a 160 ohm cord will work perfectly. As always choose the nearest available value."
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