As far as the positive/negative question, the transformer would not know the difference. It will work on either polarity. However, if you are intending it to replace the Lincoln 7ML080 transformer with the Firestone 4B-72 transformer, there is a major problem besides the difference in physical layout. The Firestone transformer does not have enough voltage or amperage for the Lincoln radio. This is assuming that we are talking about the same Firestone radio. Sams Auto Radio series AR-4 lists the model 4B-72 as intended for a 1953 Chevrolet, not Studebaker. Transformer specifications are as follows:
Lincoln: (Zenith part # 95-948) Input: 6 volts @ 4.5 amps, Output: 560 VCT @ 60 ma.
Firestone: (part # TV-100) Input: 6 volts @ 2 amps, Output: 430 VCT @ 46 ma.
I don't know why the power supply you built did not work, possibly a bad solid state vibrator? Defective new ones are a distinct possibility. Did you try your supply with a good mechanical vibrator?
Hope this helps,
Meade
::I hava a Zenith Auto Radio Model 7ML080 positive ground . came out of 1947 Lincoln. The Vibrator transformer had shorted and smoked. I built a power supply using a Vib.transformer and a positive ground
::solid state vibrator I bought from Antique Auto radio.
::could not make it work. I have a Firestone Auto Radio
::model 4-b-72 (studebaker) negative ground. Can a positive ground power supply be built using this negative ground Studebaker Transformer
::Thanks Darrell