Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Sat 16, 2017 11:54 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 17 posts ] 
Author Message
 Post subject: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 6:48 am 
New Member

Joined: Sep Wed 13, 2017 11:55 pm
Posts: 20
Hi guys,
Probably should have thought of this before purchasing my Delco 3201 but I liked the radio so.....
Anyway, can anyone direct me to some instructions and/or plans for putting together an adequate (and hopefully inexpensive) power supply for it? Thanks in advance!
Mike


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 7:26 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11950
Location: San Jose, CA USA
Here's what I use for my 3208:
Attachment:
Delco 3208 Power Supply.png
Delco 3208 Power Supply.png [ 141.33 KiB | Viewed 409 times ]

This is just a "junk box special" built from parts I had on hand many years ago when I got my Delco. But it shows some general design ideas that work (in this case, zener regulation with a pass transistor to jack up the current to the needed level). There are lots of other ways to do it as well. There was a thread on this subject within the last 6 months, which you might search for.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 10:56 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25749
Location: SoCal, 91387
Another source would simply be an HP printer power supply;
https://www.ebay.com/sch/i.html?_from=R ... ly&_sop=15

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 1:33 pm 
Member

Joined: Jul Wed 22, 2009 3:07 pm
Posts: 658
fifties wrote:
Another source would simply be an HP printer power supply;
https://www.ebay.com/sch/i.html?_from=R ... ly&_sop=15

That is a switching power supply, it could be noisy.
I would go with the linear PS.

Peter


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 4:07 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25799
Location: Detroit, MI USA
There were linear HP 32 volt printer supplies a decade or so ago as well. You can tell which are which by the weight.

That homemade supply would be quite simple to assemble and raising the voltage of one of the zeners could get the output closer to 32 volts, although that isn't critical.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 7:14 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 2211
Location: Lexington, KY USA
As Tom explained, his schematic shows what he built using parts he happened to have at the time. If you have to buy new parts, some adaptation would be a good idea. Just price one of those 5W zeners!

The same general idea can still be built inexpensively. The real key is finding a suitable transformer. You might use a 24V transformer in series with a 12V one. There should be suitable surplus transformers out there.

As to the pricey zeners, if you sub-in a darlington transistor, you can use a single 1W zener. An IC voltage regulator is also a good choice these days. If more current is required, you can parallel regulators, or add a transistor to boost a regulator's output.

I think I recall a thread where even the HP switchers had worked well for someone. If you can come across one cheap enough, it might be worth trying.

Do you know how much current the radio draws? That would help suggestions here be more specific to your actual needs.

Ted


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 7:19 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36074
Location: Livermore, CA
I've used 2N3055, like Tom. There is a 2N6055 darlington available. It has a min gain of 750.

http://pdf.datasheetcatalog.com/datashe ... ry9ewy.pdf

http://pdf.datasheetcatalog.com/datashe ... 2N6056.pdf

_________________
Norm


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 8:51 pm 
New Member

Joined: Sep Wed 13, 2017 11:55 pm
Posts: 20
Guys,
Thank you all so much for the suggestions. I'll research them all and pick the one that works for me.
Appreciate it!
Mike


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 9:49 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 25749
Location: SoCal, 91387
Usually Lurking wrote:

Do you know how much current the radio draws? That would help suggestions here be more specific to your actual needs.

Ted

Easiest way to tell is to look up the tubes in the RCA receiving tube manual, or an online source, and add each one's current requirement together.

I've built AC supplies for two of my higher current requirement Zenith farm sets, simply using a power transformer (IIRC about 2.5 amps), Diode Bridge made out of four 1N4007's, and an Electrolytic filter cap (I think about 10 mFd). These sets don't really require a strict voltage regulation. Remember, consumer circuits were supposed to tolerate +/- 15%.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 11:00 pm 
Member

Joined: Jan Tue 16, 2007 7:02 am
Posts: 2211
Location: Lexington, KY USA
There is a Rider schematic here:

http://www.nostalgiaair.org/PagesByMode ... 022381.pdf

I didn't see any spec for the 32V current, but there is a 3A fuse on the DC line.

Has anyone found any data for the tubes that includes the B+ current at 25 or 32V? The 1937 RCA data for the 48 only goes down to 96V.

Safe to say that the total drain will be between the sum of the tube heater current and field coil draw and 3A. At the low voltage, even a pair of 48 output tubes won't draw a lot of B+ current.

This radio uses the 32V DC supply as B+, as well as for the speaker field. There is no audio frequency filtering in the radio for the B+. Bet you could tell by the whine when the wind started to blow.

With a 6" speaker, some pretty good filtering on an AC supply will be necessary to keep the audible hum down. The filtering is more important than good regulation. When using solid state components for filtering, voltage regulation is pretty much free. I guess if you want a period-correct design, you could use a CVT with some copper-oxide rectifiers to do the same thing. Maybe add some big chokes...

There are other farm sets that use vibrators for the B+ that will tolerate more hum and noise on the DC input. Even those may produce a strange woing-woing-woing sound when fed with poorly filtered rectified AC, as the vibrator frequency beats with the ripple.

Ted


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Sun 03, 2017 11:25 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11950
Location: San Jose, CA USA
I used to think that these 32 volt farm power systems were wind charged, but recently somebody posted some nice material showing that 32 volt systems were driven by gasoline generators to charge big storage battieries. I knew that there were a variety of appliances made for 32 volts, including irons(!). Looking at the design of this radio, you can tell that power efficiency was not the main objective, as would be the case for farm radios that ran from little dry cells. These 32 volt farm power systems had lots of available amps, and big batteries to keep the system afloat between charging cycles.

Some good comments above. If one wants to build a power supply similar to the one I posted above, but doesn't have a box full of 5 watt zeners sitting around (and no one should), I like the idea of using a Darlington transistor and replacing my 5 watt zeners with a single 1 watt 34 volt zener, or a small series string that adds up to about 33-34 volts. You want an extra volt or two on the zener string, since the Darlington will drop about 1.3 volts between base and emitter.

With a single 1 watt zener, the resistor shown in my schematic would be increased to about 470 ohms to avoid overheating the 1 watt zener. That's assuming a 36 volt transformer is used. You may have to experiment with the resistor value to aim for something like 20-30 mA supplied to combination of the transistor base and the zener.

The way I have it designed, the power supply never operates with no load. If it does, then the design should be adjusted to make sure no more than 25 mA goes through the zener at no load.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Mon 04, 2017 12:03 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21276
Location: Haledon, NJ, usa
Tom Albrecht wrote:
I used to think that these 32 volt farm power systems were wind charged, but recently somebody posted some nice material showing that 32 volt systems were driven by gasoline generators to charge big storage battieries. I knew that there were a variety of appliances made for 32 volts, including irons(!). Looking at the design of this radio, you can tell that power efficiency was not the main objective, as would be the case for farm radios that ran from little dry cells. These 32 volt farm power systems had lots of available amps, and big batteries to keep the system afloat between charging cycles.

Some good comments above. If one wants to build a power supply similar to the one I posted above, but doesn't have a box full of 5 watt zeners sitting around (and no one should), I like the idea of using a Darlington transistor and replacing my 5 watt zeners with a single 1 watt 34 volt zener, or a small series string that adds up to about 33-34 volts. You want an extra volt or two on the zener string, since the Darlington will drop about 1.3 volts between base and emitter.

With a single 1 watt zener, the resistor shown in my schematic would be increased to about 470 ohms to avoid overheating the 1 watt zener. That's assuming a 36 volt transformer is used. You may have to experiment with the resistor value to aim for something like 20-30 mA supplied to combination of the transistor base and the zener.

The way I have it designed, the power supply never operates with no load. If it does, then the design should be adjusted to make sure no more than 25 mA goes through the zener at no load.

Hi Tom:
Yeah thanks for the update...I was looking at your schematic... and wondered why you chose a 60 ohm resistor?
You have 42v you want to drop down to the Zener voltage of 32 so you're dropping 10v. But a 60 ohm allows 160ma of current into the Zeners.
Just because they are 5 watt Zeners doesn't mean they "need" all that current. They can "handle" 5 watts, yes sure, but they will operate just fine with about 5-10ma or maybe 20ma of current to keep them in the Zener-break-down zone.

So why didn't you think you could have used a 470 ohm there?

Image

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Mon 04, 2017 1:06 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11950
Location: San Jose, CA USA
Hi Peter,

The minimum hfe (current gain) of a 2N3055 is 20, so if we need 2.5 amps, the base current on the transistor needs to be 3/20 = 125 mA. I don't recall exactly what my Delco 3208 draws, but it may be around 2.5 A. The tube filaments alone are 1.9 amp, and I bet the speaker field (operating at 32 V) also draws at least a few hundred mA.

It appears I designed it to withstand a no load situation (where all the current goes into the zeners, and none into the transistor base).

Looks like the zener current could be reduced a bit. However, it can't go down as far as you're recommending because of the low current gain of the transistor. That's why a Darlington would really be the way to go if one wants less current in the zener.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Mon 04, 2017 1:16 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21276
Location: Haledon, NJ, usa
Tom Albrecht wrote:
Hi Peter,

The minimum hfe (current gain) of a 2N3055 is 20, so if we need 2.5 amps, the base current on the transistor needs to be 3/20 = 125 mA. I don't recall exactly what my Delco 3208 draws, but it may be around 2.5 A. The tube filaments alone are 1.9 amp, and I bet the speaker field (operating at 32 V) also draws at least a few hundred mA.

It appears I designed it to withstand a no load situation (where all the current goes into the zeners, and none into the transistor base).

Looks like the zener current could be reduced a bit. However, it can't go down as far as you're recommending because of the low current gain of the transistor. That's why a Darlington would really be the way to go if one wants less current in the zener.

Didn't realize the gain was so low.
You must have had to have a giant heatsink on that?

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Mon 04, 2017 1:33 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11950
Location: San Jose, CA USA
Yes - it is a pretty large heat sink.

You inspired me to dig this radio out of my closet. Plugged it in and tried after something like 20 years, and it still works just fine!

You can see the heatsink with the three semiconductor devices mounted on it. Gets hot, but not unacceptably so. Looks like I have a fairly hefty transformer on it. Not sure where I got the transformer, but it would have been salvaged from something.

I see that I don't have the original field coil speaker -- the one in there is a replacement PM speaker. So total current draw is probably a little over 2 amps. That's a 70-volt line transformer from a PA system serving as the output transformer (which was apparently lost with the original speaker).

Not sure when I built this, but my guess is that it was back in the 1990s, or possibly even the 1980s.

Attachment:
Delco 3208 front.jpg
Delco 3208 front.jpg [ 94.68 KiB | Viewed 273 times ]

Attachment:
Delco 3208 rear.jpg
Delco 3208 rear.jpg [ 109.48 KiB | Viewed 273 times ]

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Mon 04, 2017 5:17 am 
Member
User avatar

Joined: Mar Mon 17, 2008 5:05 am
Posts: 5024
Location: Ashhurst, New Zealand
oops...

_________________
Cheers - Martin ZL2MC


Top
 Profile  
 
 Post subject: Re: 32 Volt Power Supply
PostPosted: Dec Thu 07, 2017 4:13 am 
Member

Joined: Oct Sun 18, 2015 2:49 am
Posts: 109
Location: San Angelo, TX
I have a collection of Delco Light Plants, so I know a tad about them. If the engine-generator is running, the generator hash is quiet high. There are capacitors in some of them, probably added after factory. They help, but don't kill all hash. My old L'Tatro console that I haul to engine shows really gets torn up by that hash. It is a vibrator unit and as mentioned earlier, is not overly sensitive to voltage. Original setups had the batteries and generator some distance from the radio, so that also helped. My setup uses four 8 volt batteries, giving me 32 volts. They, of course, don't have the reserve of the originals, but they work fine!
I also have an HP 32 volt switching supply, but the rf noise from it is terrible. The radio works, but is not worth listening to. The Kohler engine generator that I have (starts on 32 volts, then switches to 110 AC) has what they called a "Quietus Capacitor" on it to kill some rf. It is simply a large paper cap from each leg to the frame of the generator.
This blurb hasn't been much about a 32 volt power supply, but I hope it was interesting. Denis


Top
 Profile  
 
Post New Topic Post Reply  [ 17 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: Majestic-12 [Bot] and 13 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB