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power supply to convert from 32 volt DC - Printable Version

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power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-05-2016

I have to stay away from the local auction house. Tonight I picked up a nice 1934 Coronado small console radio. It was too good to pass up at $40 with its art deco look. Well, I found out it's a series 6B, made by Wells-Gardner and was a farm radio....equipped to operate at 32 volts DC. It uses a vibrator like a car radio to supply the B+ (housed in a large metal cylinder). Here's a link to the schematic:

http://www.nostalgiaair.org/pagesbymodel/537/M0023537.pdf

My question is, has anyone had experience with these farm sets and if so what did you do to convert it for use with 120 volt house current? Is there a power supply available that can be utilized? I have the ARBE I use on my AK battery sets but would like to find something I could mount in the cabinet so it can stay with the radio. From what I've read a lot of these sets were destroyed by people simply plugging them into a wall socket to try them out, not knowing that just because it has a line cord and plug, it's not designed for 120 volts! I'd like to eliminate the vibrator if possible, as I doubt it's any good and to try to find a vibrator with a 32 volt input (it's a Radiart Vibrator Type 3395 if anyone has one laying around) is proving to be next to impossible.

I'm treading in new territory here so I'm hoping someone can help point me in the right direction. Thanks!

RE: power supply to convert from 32 volt DC - Radioroslyn - 08-05-2016

So the fun begins!
You'll need to gather up a 24v 4A transformer like this: http://www.ebay.com/itm/Signal-Transformer-A41-175-24-Class-F-1-Transformer-115-230V-12-24V-175VA-/331922771083?hash=item4d48238c8b:g:LjQAAOSwnNBXXPux 
A bridge retificer like this:https://www.westfloridacomponents.com/J691APL02/10A+100V+Bridge+Rectifier+Diode+Micosemi+MB101.html
And a large filter cap like this: http://www.ebay.com/itm/like/231725322816?lpid=82&chn=ps&ul_noapp=true

Theory tells me the the output voltage is going to be 33.6v but practical experience says it's going to sag a bit, in the real world about 30v but that will get us in the ballpark.

If you need direction in the wiring department I'm happy to help out.

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-05-2016

Thank you thank you, Terry! I'm glad to have found someone who has encountered one of these 32 volt sets and apparently has successfully made a working power supply for it. I've ordered the components you mentioned. I definitely could use your input to wire everything together based on the schematic above. Or if you could point me to a generic wiring diagram showing how to assemble it all first, then wiring it to the radio itself can follow later.

THANKS AGAIN!!

RE: power supply to convert from 32 volt DC - David - 08-05-2016

Hope this helps you can save the info as a PDF. David   http://www.ibiblio.org/kuphaldt/socratic/output/supply1.pdf 

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-05-2016

Thanks, David! Will read through it. Icon_thumbup

RE: power supply to convert from 32 volt DC - Radioroslyn - 08-05-2016

NP my friend.
To ready the transformer (the one from epay) will need to connect terminals 1 and 5 together Also terminals 2 and 6. this connects the two primary winding in parallel so it can operate from your 120vac mains. It can be configured to operate from 220vac if you find yourself in the UK.

The secondary you'll need to employ a jumper from terminals 8 and 11. This connects the two 12vac winding in series to make 24vac from terminals 7 and 12.

On the bridge rectifier there are four connections and you'll see three different markings on it. Two of the marks look like sideways S's, these are where you connect the 24vac from the transformer's secondary.  The other two will be a + and -. They will be connected to + and - on the filter cap. And then to the + and - to your set.

Couple of notes. Use a little heaver wire than 20g hook up wire. 16 should be ok. Be sure when installing the filter cap that the polarity is correct. Backwards it could go off like a M80. May want to add a power off/on switch.

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-05-2016

That's fantastic....you're awesome Terry! Was a bit concerned about the transformer only being at 24v as opposed to the 32v the set is rated at. This should be OK?

So, in theory, I should be able to just eliminate the big metal cylinder containing the vibrator (B power unit as it is called on the schematic) and this can be used in its place?

I really appreciate your patience with me and your most generous help Icon_clap

RE: power supply to convert from 32 volt DC - David - 08-05-2016

The power supply project replaces the 4  8volt batteries that would have been part of a windmill power supply. The vibrator is needed to step up the 32 volts to the required B+ for your radio sorry. David

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-05-2016

Ah that's what I thought. Thanks David. Looking at the schematic more I finally found where the vibrator unit ties in. Oh well. Maybe I'll get lucky and the vibrator will still be good.

RE: power supply to convert from 32 volt DC - Radioroslyn - 08-05-2016

Was a bit concerned about the transformer only being at 24v as opposed to the 32v the set is rated at. This should be OK?

Well how it works is that different types of rectifier setups the output voltage can be different than the ac volt supplied from the transformer depending on how much of the ac wave is rectifed. In this case with a full wave bridge rectifier it's rectifying both the negative and positive cycles of the ac so the output volt is equal to input X1.4 (24vX1.4= 33.6vdc)
Half wave rectifiers are input X.9 Voltage doublers are X2 full wave are X.5

Yes you will need to have the vibrator. What the vibrator (or chopper as we use to call there in the old dayz) does is it chops or pulses the 32vdc on to the primary of the power transformer. Transformers must have ac or pulsed dc on them to operate. If you apply dc across the winding of a transformer all it will do is get hot and if there is enough dc voltage if will burn out the winding. The vibrator doesn't step up the voltage it makes it look like ac so it can be stepped up by the power transformer.

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-06-2016

Thanks again, Terry. That makes sense as to why the transformer will work. I appreciate you taking the time to give me such a thorough explanation! I'm sure I'll have more questions once all the parts for the power supply I've ordered arrive. In the meantime, it's cleaning the chassis and doing some checking of components before I tackle capacitor replacement.

RE: power supply to convert from 32 volt DC - Radioroslyn - 08-06-2016

Perhaps the 1st order of business is to make sure the heaters are good in the tubes If not this may be an indication that somebody has plugged it to a 120ac outlet That's a game changer!

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-06-2016

Definitely going to do that first...right after I de-fuzz bunny the chassis Icon_smile

RE: power supply to convert from 32 volt DC - NostalgiaRadioTime - 08-08-2016

So far so good, the heaters are good on all of the tubes and....amazingly...both dial light bulbs still light (with my test light)! I think I lucked out that nobody fried this at 120 volts or certainly the tubes and bulbs would be toast. .

I received the big capacitor today...just waiting on the transformer and bridge rectifier. Should have those before the end of the week. My biggest concern now is...will that 32 volt vibrator still work. That could potentially be a dealbreaker, as I know 6 and 12 volt vibrators are fairly common but 32 volt are pretty scarce. I may post a want ad on here for one just in case.

RE: power supply to convert from 32 volt DC - David - 08-08-2016

 Before you fire up your set see if you can clean the points and replace the caps inside the vibrator. If using sandpaper on the points be sure and remove all the dust from cleaning. David