How do you know if an amp is putting out enough voltage/ current?

Not enough volume and higher distortion as you turn up the volume.

If it doesn't tame the highs and add bass, then it needs more juice.  That is the head-fi way.

Not enough voltage = not enough volume.

Not enough current will cause early clipping on dynamics especially in the bass. This is because when a driver is at rest or playing softly the amp has to get the driver moving pronto & until the driver gets moving & starts generating back electromotive force the amp is looking at the actuall resistance of the driver windings rather than the significantly higher driver impedance characteristic which is made up of driver winding resistance + the back electromotive force which is affected by the size of the  the cabinate, the weight of the driver, the number of turns inside the magnetic gap of the voice coil, the sprigyness of the suspension cotrolled by both the stiffness of the spider & the stiffness of the airspring caused by the cabinate as well as whether the cabinate is ported or not or if it is horn loaded or not & so on. Lots of variables here that effect driver impedance that are not in play when the driver is at rest.

Quote:

Originally Posted by germanium 

Not enough voltage = not enough volume.

 

Not enough current will cause early clipping on dynamics especially in the bass. This is because when a driver is at rest or playing softly the amp has to get the driver moving pronto & until the driver gets moving & starts generating back electromotive force the amp is looking at the actuall resistance of the driver windings rather than the significantly higher driver impedance characteristic which is made up of driver winding resistance + the back electromotive force...

Where did you get this idea from?

se

I have tube amps that I manually bias. At low voltage, it sounds thin like listening to an AM radio station from a table-top transistor radio. Once its bias right, its full sounding and dimensional.

Many low powered tube amps for headphones have auto-bias which is good.

Quote:

Originally Posted by wuwhere 

I have tube amps that I manually bias. At low voltage, it sounds thin like listening to an AM radio station from a table-top transistor radio. Once its bias right, its full sounding and dimensional.

 

Many low powered tube amps for headphones have auto-bias which is good.

I don't get it. You mean you have tube amp that allows you to adjust the voltage supply (Vb) and current source (peak current). Why do you need to do that? I think that could create more problems than it solves.

Btw, biasing tubes doesn't seem to have anything to do with the OPs question.

Quote:

Originally Posted by dvw 

I don't get it. You mean you have tube amp that allows you to adjust the voltage supply (Vb) and current source (peak current). Why do you need to do that? I think that could create more problems than it solves.

The bias voltage or current is applied to the cathode. For a 6550 output tubes, its usually set between 40 to 50ma. There is a trim pot per output tube. There is a resistor, usually 1ohm in-line to ground between the cathode and ground. So the voltage through this resistor is the current in milli-amp. I measure this voltage. Now yes, if you set this voltage too high it will destroy your output tube.

Quote:

Originally Posted by xnor 

Btw, biasing tubes doesn't seem to have anything to do with the OPs question. He's asking about amp output, not what's going on inside.

I know that, but to understand the output, what happens inside is very relevant, but whether he is interested or not is his prerogative.

I'll consider distortion as a sign that your amp is approaching its voltage limits.

The max current will be limited be the amp design. So I'd say not much change even if you turn the dial up, because the amp simply cannot supply more current.