I have an original 1954 Hudson Sylvania radio that runs on 6V positive ground, and want to convert the radio to run on 12V negative ground.
I've read a lot of posts, on this forum and elsewhere, describing various approaches. The first step is to replace the original vibrator with an electronic version (in a 4-pin can) that uses a negative ground. The variations on what else to do include:
1) Replace the vibrator with a 6V negative ground unit. Use a power resistor (e.g., 1.6 ohm, 70 - 90 watt) to drop the car's 12V to an effective 6V. This solution is coarse and failure-prone because the radio current draw changes as it warms up, so the initial voltage drop will be too small, thus running the radio at too high a voltage until it warms up. Also, you have to be careful not to burn your hand when reaching under the dash, and you are basically wasting as much current heating the resistor as it takes to run the radio, which is a lot to begin with.
2) Replace the vibrator with a 6V negative ground unit. Use a solid-state voltage regulator to drop the car's 12V to 6V. This solution is reasonable, but you have to be careful to get a high power regulator, such as the SMAKN® Waterproof DC/DC Converter 12V/24V Step Down to 6V/15A 90W Power Supply Module. I am going to try this converter, and will report back on its suitability. It costs less than $25 for the regulator, and about $25 for the vibrator.
3) Replace the vibrator with a 12V negative ground unit. Replace each tube with a 12v equivalent. In my 1954 Sylvania Radio, it turns out that 7 of the 8 tubes have direct replacement 12V equivalents, but I cannot find a 12V replacement for the 6C4 tube. To do that last tube, I would have to use a 12V tube with a different socket. Replace the transformer out of the vibrator (since it is designed to step up 6V AC and now needs to step up 12V AC). This solution is elegant, but takes some rewiring of tube sockets and a transformer to do right. The total tube cost plus socket is somewhere in the neighborhood of $120.
4) Hire HET Radio Adviser to do the conversion, which I believe is on the order of $400. That might include the option of an FM tuner and AUX inputs.
I am trying solution 2, since the cost is minimal compared to 3 or 4.
One more thing -- You can get the radio to amplify an external signal by attaching a mono input across 2 contacts on the volume potentiometer. So it is possible to attach an iPod or FM tuner to the radio, and get the radio to amplify it. Whether it is worth doing is a question for another day.
Follow-up 7/31/2016: I was successful with approach 2 and the SMAKN® Waterproof DC/DC Converter 12V/24V Step Down to 6V/15A 90W power supply. This supply does not get hot at all. I attached it to the side of the radio and it works well.
Check out RediRad, @ www.rediscoverradio.com
That's what I have in my stock Hudson radio for only $99 with no modifications. Sound is very good.
The RediRad sounds like a good solution for the part of the exercise I left for another day! Thank you.
I also converted my 54 Hornet to 12 volts negative ground. The mechanical (but not the solid state) vibrator will work with either positive or negative ground (as will the radio), so I used a 12 to 6 volt DC to DC converter as suggested above and the radio works fine. I also use the RediRad in both my Hornet and a 51 Pontiac and it works fine. I agree that making two connections across the volume control would work fine, too. Partly out of laziness and partly out of a slight desire to keep the radio stock was the reason I used the RediRad. I used an identical DC to DC converter to step down the voltage to the heater blower, too.
I know converting from 6 to 12 V is a bit controversial. Just before the conversion, I installed a 6V Optima battery and I was amazed at how fast it turned over my Hudson. I went ahead a few years ago with the 6 to 12 conversion mainly because of a trip I made in my 51 Pontiac from Seattle to Dallas in 2013 ( http://fugutabetai.com/?postid=520). When I started the trip with my son, I thought because people drove 50s cars all over the US even in the 60s and early 70s, that we should be fine. What I realized too late was that in the 60s and early 70s, you could get parts for 50s cars at any parts store or even some gas stations. However having fuel pump (switched from mechanical to electrical on the trip) problems and later generator problems made me decide to go to 12 volts with my Hornet. I will likely do a similar cross country trip with my Hornet later this year...
Dr. Bob, I'd like to offer a couple of corrections.
Re your item #1, the initial current drawn by the radio is higher than when it's run for a few seconds. If the resistor is sized for steady-state operation, any stress at initial turn-on is going to be on the resistor, not the radio.
As for your #4, HET radio adviser Steve Engel advises that for a typical stepdown era radio, his price for a full changeover to 12v neg ground (i.e., all new power transformer, vibrator, 12v tubes, etc.) is $200, not $400. For me, that would put his full conversion at the top of the "solution list."
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