View Full Version : OT voltage in a radio reciever?

01-12-2007, 04:16 PM
Hey guys - this is off topic, but does anyone know what kind of voltage a power supply in a nice radio reciever is capable of?

I've got an Onkyo power supply tagged NPT-1368D - pretty heafty and the reciever was pretty nice with all sorts of extra features...

01-12-2007, 04:30 PM
Solid state?

01-12-2007, 04:35 PM

its oldish and the power source / transformer is heavy metal clad cube with solid copper band around the outside. Kinda looks like a solid state ignition systems...?

01-12-2007, 05:00 PM
I mean the radio itself. Does it have vacuum tubes?

01-12-2007, 05:02 PM
Nope no vacuum tubes

01-12-2007, 05:07 PM
Then it will be a low voltage supply, most likely somewhere around 12 volts.

Steve Stas
01-12-2007, 07:45 PM
Evan is right it's probably 12 volts, although it could be as low as 5Volts or as high as 18. You can measure that easily enough with a cheapo radio shack meter. Issue is though, it's difficult to tell how much current it can deliver without burning up. Unless it directly drove Hi-wattage speakers, it's probly only a fraction of an ampere in current capability. If it was a component radio -part of a syste, with a separate amplier, it's likely low current. If it's got a fuse in it, naturally the max current will be aout 20 % less than the fuse rating.

steve Stas

01-12-2007, 10:31 PM
If it is a really old set from the germanium days it could be 6v or less, but silicon transistors are commonly run at 9v or more. There is a riveting discussion of the subject here:


Yoost kidding, ya!

01-12-2007, 10:45 PM
It is very common to run such radios on nominal 12 volts. That is the case with my old Yaesu FRG-7700 since it makes it possible to easily run it from a car battery.

J Tiers
01-13-2007, 12:29 AM
Very possible that it is around 25V raw output.

Not uncommon to double zener regulate the supply for the local oscillator (s) for stability. In that case, the higher voltage gives room to do it and still get a reasonably high final voltage like 12V to operate it.

Most likely there is also a lower voltage around 6 or 12 V to operate the dial lights, at a medium current, around an amp or two. That, if it is older, like 70's vintage. Newer ones got away from the "dome light" bulbs for dial lights.

I used to repair for a shop that was warranty authorized for 50 brands of hifi stuff. Been a while now, but most of the tuners had several voltages in them.

01-13-2007, 01:32 AM
You're calling it a receiver- that says to me that it's a home stereo component. If that's the case, if it's an older unit, it would probably have a single voltage supply that runs the amplifier section, and that voltage would be around 30 - 50 volts after being rectified. That means the ac output of that transformer would be from 20 to maybe 35 volts. A newer type receiver would have twin power supply voltages, probably in the range of + and - 25 to 50 volts.

The radio sections in most receivers run on 12 volts, some are fed more.

You have described a power transformer which has a copper band surrounding it- this reduces hum in surrounding circuitry. That doesn't say much, since that technique has been in use for several decades, but it does say that the manufacturer paid some attention to making the unit a better performer, humwise at least.

You could probably give a little more info on that power supply, and we could decipher the wiring on the transformer.

If you're talking about a power supply, as in a complete and separate unit, then probably things are not as I am assuming.

J Tiers
01-13-2007, 01:41 AM
Yes, if it is a "receiver (I missed that, got the idea it was a tuner....) then teh main power amp voltage "rails" will be a voltage related to the power output of the thing per channel. That is due to the amplifier power supply being the limit of peak voltage.

If for instance it was a stereo receiver, about 50 w per channel at 4 ohms, I would expect a power supply of about + and - 25V, at a current capability of about 4A or 5A long term.

Other powers would require different voltages.

There are probably other lower voltages for low power preamp circuits, tuner, etc. They might be derived from the main voltage, or the might be separate. The Japanese often used a separate winding for lower voltages rather than regulate down from a higher voltage.

Paul Alciatore
01-13-2007, 02:04 AM
If you are looking for an inexpensive DC power supply for a project, look at a surplus computer store. Computer supplies provide five and twelve volts at pretty respectable current levels. And you can probably pick up a used one for a few dollars.

Also many of the mail order or web based electronic parts companies have a variety of supplies available for reasonable prices. A web search would probably turn up hundreds of them. Avoid the top line ones like Newark as they will only have top line (expensive) units.

01-14-2007, 06:15 PM
Well i finally got around to testing it - after a few of those forehead slapping, "d'oh" moments. (i started off testing for dc voltage and couldn't figure why i wasnt getting a reading ... haha d'oh)

So here's the news:

120 vac input 8 amp

Output (10 pins)

34 - 0 -34 vac

18-0-18 vac

11.4 vac

5.2 vac

So i planning on using this to power a couple off odd-ball creations, one will be a motor to spin up my gyroscope (to heavy and smooth to power by air - i tried) and the main use is the 11.4 volts to a impact coil pack from a car to crank out some heavy duty dc voltage. I'm working on a jacobs ladder, but i'm worried about the amperage my coil will require.

01-14-2007, 07:03 PM
That's too cool - I've always wanted to build a Jacob's ladder. Are you buying the Tesla coil or going to wind it yourself? Make sure and post a picture when you've got it going.

01-14-2007, 07:28 PM
A few things about a Jacobs ladder: You can use a neon sign transformer or the ignition transormer from an oil furnace. The ladder should be inside a clear tube, acrylic is good. That helps the arc climb as it is heated air that pushes it up. It also makes it safer.


A jacobs ladder produces large quantities of ozone. This can be bad for your health and extremely irritating to your respiratory tract.

01-14-2007, 08:28 PM
Thanks for the tips Evan

I already considered the neon light transformer - but that means i have to buy one or find one. I've already got the impact coil so i'll see what happens with it.

I also thought about the ozone issue - i figured it will either be on for short durations or used in an outdoor setting

I read somewhere that, although the enclosure makes it safer, it makes it less effective. Not sure i buy it though since, as you noted, it ought to help the movement of the arc

01-14-2007, 09:53 PM
Ok, on your transformer, the 34-0-34 winding will have a fairly low resistance, it's possible the 18-0-18 also has a low resistance- the 11.4 volt winding might not have a really low resistance, and the 5.2 well, same goes there. The main power being delivered by that transformer is through the 34-0-34 vac windings. It's quite likely that it's not suitable to deliver substantial power through the other windings. Make some ohmeter readings and post the results. We'll save you some grief if you're expecting a good solid 12 v output and it can't deliver for you.

J Tiers
01-14-2007, 11:01 PM
nary a one of those will give you 12V.....

One will give you around 8V, another around 15V, the others will give higher voltages. Those voltages are peak.

Loading will reduce the average volts, but the "peak ripple voltage" will still be closer to the peak volts, depending on winding resistance. And, at lower loads, teh voltage will rise towards the above.

Yes, the lower voltage will be lower power, and almost surely only capable of lower current, maybe very much lower current.

01-14-2007, 11:58 PM
The 34 vac to zero reads .25 ohms
The 18 vac to zero reads .8 ohms
The 11.4 vac reads .5 ohms
And the 5.2 vac reads .6 ohms

34vac to 34vac reads, of course, .5 ohms and so forth

01-15-2007, 02:10 AM
Fastrack, those resistances indicate that the 11.4 v winding would give you about two amps output, dropping the 15 volts or so no load output to about 12 or so volts under load. As you load it down further, output voltage drops farther.

The lower voltage winding could be wired in series with the 11 v winding to give a bit over 20 volts dc (after rectifer and with filter capacitor, of course) and would still be hard pressed to give over two amps without dropping the voltage too far. That's decent enough for an experimenters power supply, but you wouldn't expect more than a couple amps, a bit more for short periods if you can accept more of a voltage drop. The regulation wouldn't be very good, but of course for a lot of things that wouldn't matter. If I were using that as a power supply for a tesla coil or such, I would figure that it's good for about 50 watts.

The 34 v winding would give you about 5 times better regulation from no load to the same 2 amp level, but of course the voltage output is higher- about 45 to 50 volts, or 90 to 100 volts if you ignored the center tap and went with the 68 volts ac to bridge rectifer and filter. The output from that winding would probably be rated at something like 200 watts.
As far as the 18 v winding, it would deliver about 25 volts or so dc, at no load, and would probably be good for about 20 volts at 2 to 3 amp range.

I'm pretty sure the lower two voltage windings are separate, but the two higher voltage outputs might share the centertap. If that's not the case, then you could build yourself a power supply with many separate outputs, which could be put in series to add the voltages. Having dc outputs of about 8, 15, 25, and 45- that could be useful depending on what you would be playing with. 100 volts can also be useful, maybe for testing treadmill motors, but not for getting lots of power out of them. That transformer you have is probably rated at 200 to 250 watts- that would be a total of all outputs.

Realistically, by different combinations of windings you could have several reasonably well spaced output voltage levels, ranging from 5 vac up to 84 vac, or from 8 vdc up to about 115 vdc. As JTiers says, you don't have 12 vdc anywhere, but you do have one which will load down to about 12v with around 2 amps draw.