Carbon dating calibration
Obviously, this wouldn’t appear ‘right’ to the technician, and he would go on to use a ‘better’ DMM.However, for demonstration purposes, the technician decides to use a VTVM, with an isolation probe.Today’s DMM can achieve comparable accuracy, yet there are still instances where a VTVM is the only meter to have!Next, we will see a case where the faster response to any change in the voltage being measured comes in handy.Many of today’s tube ‘experts’ do not seem to own a VTVM, and I am always puzzled by this.To give you a basic understanding of what a VTVM is, and why it is so valuable, let’s start with a crash course. At the end of the ‘Lesson’ I will impart with a book list that can help you become a better technician in no time flat!Now the voltage divider action results in a voltage reading of 49VDC, which is pretty close to the ‘expected’ 50VDC.Hopefully, you can understand how much this accuracy was appreciated some sixty years ago.
If you want to be serious about servicing vintage tube amplifiers, you should make a routine habit of checking any coupling capacitors for leakage.That is, the input resistance is 10Meg, whether the range switch is operated on the 1-volt position or the 100-volt position.Accordingly, the ohms-per-volt sensitivity changes with the range selected.On the outside, the meter looks like a typical old-fashioned analog meter. Despite the differences in outward appearance, probably 99% of VTVM’s have the identical circuit inside the cabinet.The heart of every VTVM is the balanced bridge circuit. ), and the execution of this basic principle does not seem to have changed. You should note that the input resistance is constant though out the range switch.