Using a Digital Multimeter for the first time

There is no reason to shut the amp off prior to measuring. You are actually measuring the voltage drop across a resistor under the cathode that is in series with the tube to give you the plate current.

V = I x R

You do want to wait until the amp is fully warmed up before adjusting the bias.

The meter is parallel to the resistor and so much higher in value that it effectively doesn't change or affect the reading.

The big difference in digital vs. analog meters (other than the convenience if it is auto ranging) is the digital meter has a much higher input impedance. This means it will have less effect on the circuit and give more accurate voltage readings.

Correct me if i'm wrong.Your suggestion is to insert the leads of the volt meter into the jacks of the amp.Then turn the amp on and wait at least 30 minutes before taking a reading.

If this is correct can I play music while the meter is attached to the amp?

No..... Without any signal applied to the Amp's inputs. The Amp needs to stabilize. It cannot do this if you are playing music.

Jea48> Thank you for your advise.
Herman> This morning I warmed my amp for 30 minutes and with the amp on I inserted the leads from my voltmeter.I turned the meter on and the amp started to smoke.I shut everything off, removed the leads and let everything cool down.
I powered the amps back up and everything was fine.
I then followed the instructions of inserting the leads turning the meter on and then powering up the amps and left it that way for 30 minutes and then took the reading.This worked perfectly.
I agree with your method and have always biased that way.I have know idea why my new Radio Shack voltmeter operates differently.

Mr O- In my previous post I was stating the method that works for my Cary amps, not suggesting you try the same. There are too many variations on the bias adjusting theme to make generalities. Glad you found a method that works without the smoke issue!

when you smoked your amp, where you in voltage or current mode with your digital voltmeter?Did it have a bad smell? if it did, you should have your resistors checked out, if you find any smoked, replace it for it has increased in resistance which will effect that circuit in the long run.