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Title: Ballast tube Post by: wa5ddz on April 13, 2013, 08:45:44 PM Hi all: I am restoring a Hallicrafters S-77. The ballast tube R-38 is
missing. Anyone know where I can get this ballast tube R-38 ? I did try the naval jelly on the rust as suggested on this forum. It worked very well. Just takes some time. Thanks -- Bruce Title: Re: Ballast tube Post by: Edward Cain on April 14, 2013, 05:20:28 PM Hi Bruce,
I don't know where to get a replacement tube but there is a resistor modification in at the end of the S-77 manual on BAMA. http://bama.edebris.com/manuals/hallicra/s77/ Ed Title: Re: Ballast tube Post by: KA0HCP on April 14, 2013, 05:35:17 PM I did some research last night but was not able to post. The part R-38 is actually a 24B875. A resistor network mounted in a metal can, that provides dropping resistance for different voltages. Various references indicate that it drops 30V at 300mA. Pinout may be available but it does not specify the actual internal resistances. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
It may be possible to reverse engineer the internals given the pinout, the info above and an analysis of the schematic. There are at least two threads on www.antiqueradios.com for the this radio. One mentions an alternative or cross reference ballast tube number, which I did not find readily. I could not find any for sale. Two places that should be researched next are Riders, and Sam's Photofacts. There is another source of information, a book on Ballast Tubes published in 1991, but now out of print. My apologies for not being more specific but I was under the weather and didn't make notes. Good luck on your search. bill |