Delco radio for 57 Wonderbar
The 57 Corvette radio uses a separate Solid state inverter and audio amplifier while the radio is tubes. To power the tubes is an inverter on the unit behind the speaker. That inverter uses a filter choke as part of the power supply PN 7268195. I am building a supply but the schematic gives a DC resistance value for the choke of 58 ohms. It does not give the inductance value in Henrys. Does any one have a choke for that power supply and can see what the inductance is in henrys or a Manufacturer's PN or some other reference so I can find a replacement. Or send me a picture of that inductor. The picture on the sams is not clear enough for reading. Thanks
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Re: Delco radio for 57 Wonderbar
Theodore, I'm very rusty and had to research. Could the 58 ohms on the schematic be the value of XL (Inductor Impedance)?
XL = 2(pie) fL
If the frequency is known could you then calculate L ?
I actually found the part# in the Radio Parts book but no value is shown.
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Re: Delco radio for 57 Wonderbar
Thanks for the reply. Yes I am familiar with the formula. I am an electronics component designer. I am pretty sure the 58 ohms is the DCR of the winding. All the other interstage and ouput transformer show the DCR of the windings and also the turns ratio. Thanks for the reference. TedComment
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Re: Delco radio for 57 Wonderbar
Theodore,
I also was in electronics before retirement, but mostly in the digital arena. Analog was always a challenge for me.
Only other thing I could think of is to inquire with one of the radio repair shops that advertise in the Driveline. Maybe they could share the value for you. One that was excellent was Jerry Rudbeck, but he's retired too.
RichComment
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Re: Delco radio for 57 Wonderbar
Theodore, not sure just what you are trying to do, but the original design used Germanium transistors which were inherently unreliable and are all but impossible to find. Germanium transistors of that era did not hold up well when switching inductive loads. The same was true for the audio outputs. They were packaged in a round, Delco Radio unique package. Not sure what frequency the inverter ran at, but for sure it was very low, probably a few kHz or so. In 1956 that was pushing the technology limits of the day.
I take it you don't have one to measure. If you are designing a modern day circuit, then I would design it around current MOSFET technology, running at a very high frequency, and hide it somewhere out of sight. If you are looking to have it judged, then this is what I would do and leave the old transistors as place setters. They were usually DS-501/DS-503 (DS = Delco Semiconductor) transistors, but they are listed here as 2N278 and 2N290.
Assuming you are looking at Chevrolet model 3725156 in Sams Folder 366, L10 is the choke in the output Pi filter network of the B+ feed. Looking at the picture in the Photofact folder, it appears to be a small, either air wound choke or maybe wound on a ferrite rod. Does not sound too critical.
The input capacitance of the filter is 20uF, but the output capacitance is only 0.25uF, which is very small and probably meant to filter harmonics of the oscillator. 0.25uF is very low compared to other typical designs of the time, including vibrator designs, that ran at 60Hz. For your design, if you assumed the frequency was, say, 5 kHz, you probably would not be too far off. You could build it, designed around 5 kHz, and then see how well it suppresses the harmonics. You do not need this choke to build the inverter, it is just to filter out the harmonics.
You are probably right about the resistance in the Sams folder. It is probably DCR. And if you can make contact with Jerry Rudbeck he would probably know the frequency they ran at. He is very good, I have had several very good conversations with him before he retired.
Good Luck
-Dan-Comment
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