Determining AC vs DC

[petemoore]

I have this printer adapter...says 30v output.
 Is there some way to determine if it's DC or AC?
 I have a printer adapter that's 30VDC, so my thinking is [^] one is DC, but I'd like to be certain first...
 Second...can I damage anything in a simple tube circuit [12ax7] by hooking it up to 30VAC?

[gtrmac]

I would assume that you wouldn't want to run the filaments on a 12AX7 at 30VAC.

[petemoore]

Filaments=Heaters...no, I think they're only supposed to get 6.3v or 12v, depending on how they're tapped.
 Do you know if the voltages I just typed are supposed to be AC only?
 I want to run the circuit side at a higher voltage if that's not  contradictory to 'usual' PS voltage wiring.

[niftydog]

multimeter.  pretty much a must have if you're gonna be doing DIY electronics.

Have another look at the adapter, it might have something like a sine wave following the voltage spec.  This would indicate AC.

Or it might have something like this;

Code Select Expand

___
---
this signifies DC.  Think of it like a trace on an oscilloscope, the dashed line represents ground and the solid line represents the DC voltage.

[petemoore]

I haven't actually seen the dapter, I'ts part of my buddies junk printer.
 Thing is that the DMM reads DC and AC, either way [well I don't really know]...at any rate I couldn't really discern one from the other with my tries...I'll get out the manual tomorrow.

[csj]

Just plug it in and measure it for either. Assume a center pin positive. Clip the black lead to the barrel. See which one (AC or DC) gives a steady read and which one makes the the meter reading deflect or fall flat.

[niftydog]

you won't see the meter changing much if its AC at 60hz

AC supply SHOULD read very close, if not spot on, zero volts when set on DC range.  It should ALSO read close to the given specification on AC range.

DC supply will read hardly anything on AC range, and close to spec on DC range.

It might read something on both AC and DC, but one measurement will make a hell of a lot more sence than the other!

Other way to tell; look at the power input of the printer, does IT have any specifications printed on it?

Other other way to tell; open it up.  If it's just a transformer and (possibly) a resistor or three, then it's AC.  If it's got a big cap, a regulator or diodes, then more than likely DC.

[petemoore]

That WUZ a misnomer question..
 I'ts my buddies printer adapter, and I was getting relayed partial's info's from him.
 Once I see the dapter, odds are I'll be able to figure that ac/DC thing out N/P...probably has the -----____ type lines.. or ~_ to indicate what type of current right on there...

[Ge_Whiz]

Bodge a connection from the PSU to a LED with a 3k3 series resistor. The LED will only light one way round for DC, both for AC. Or wave the LED through the air - if connected to an AC supply, you'll see the flicker.