[NJARC] Need values for BL 42 D Ballast Resistor

Thu Apr 2 13:42:04 EDT 2015

For whatever reason, this answer to Phil's question never appeared in my sent folder so if you already received this post, please excuse the reposting.

Phil
Decoding the number according to the Standard RMA Designation Code:B = ballast action for the pilot lightK = 6.3 volts @ 150 mA for brown beaded lamps, i.e. #40, #47, or 184742 = Total voltage drop of the ballast, including pilot lights, with 300 mA of currentD = wiring diagram
It looks like one pilot lamp is between pins 7 & 8, a second pilot lamp is between pins 8 & 2, and the remaining 30 volts @ 300 mA is dropped between pins 2 & 1.
Taking it a step further, the "hot" resistance between pins 7 & 8 and 8 & 2 would be 42 ohms and between 2 & 1 is 100 ohms.  I would use a standard value 43 ohm metal or carbon film or perhaps wire wound resistor at 2 to 3 watts and a 100 ohm wire wound resistor at 20 watts for substitutes, if you are so inclined.  
Ballast substitutes are: KL-45, 23-55-1, 23-55-A, URB-004 and the JFD Type A with some modifications.  I checked my stash of ballasts and unfortunately, I don't have what you need.
I feel that the need for a ballast tube to regulate current in a radio has long passed.  Perhaps from the 1930's to 1950's when the line voltage varied quite a bit from the 108 to 125 volt limits, the ballast tube was useful but now that is really not the case.  There are so many more distribution transformers (pole pigs) now in use, do to the high demand for AC power.  The line voltage now hovers, at least in my neighborhood, within a volt or two to the old maximum line voltage of 125 vac.  
Collins Radio says essentially the same thing in their R-390 Finial Engineering Report of September, 1953 but kept the ballast tube in the R-390 and R-390A because of the Signal Corps requirements for oscillator stability.  The ballast tube (3TF7) did reduced the +- 15% line voltage variation specification to a 3% change in the oscillator tube heater voltages.  But the Collins engineers felt that with the unknowns of tube ageing and all of the brouhaha of tube reliability in the early 1950's, it wasn't worth the effort to request a change in the spec.Jim

   From: Phil Vourtsis <philvourtsis at gmail.com>
 To: NJARC Reflector <njarc at mailman.qth.net> 
 Sent: Wednesday, April 1, 2015 8:56 AM
 Subject: [NJARC] Need values for BL 42 D Ballast Resistor

I picked up a GE J62 radio at the Charlotte AWA meet in beautiful condition. But one of the tube sockets was empty. Turns out it needs a ballast resistor. Does anyone have a list of these and what resistors values are? I'm looking for a BL 42 D. I checked the schematic and it shows 3 resistors but no values.
Thanks,Phil V
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