Some of the older scopes were lacking in the calibration of settings for voltage.
However if you have a Tube tester you have a reference that is easily available. It has Filament voltages.
If you want to use them as a reference, just remember to do a little math. To calibrate the P-P voltage. If you need to read a 200 volt source and you don't have one. you can use the tube tester and set it on the 70 volt position for the filament. Multiply 70Vac ( actually 71.5 Vac-rms)
by 2.8 to get
200 Vac P-PIf you don't have graticule's on the scope, then use a grease pencil and mark the screen so you have a mark at 0 inches and 4 inches, then make a mark at exactly 2 inches then between this center, mark 1 inch marks top and bottom of the center marks. These become your reference for full screen deflection boundaries of a a 200 volt P-P sine-wave. So if you need to check an ac voltage of less than 200 volts this will be your screen reference. When you set this up you only want the vertical gain set to make this adjustment. After this don't move the gain control. Make sure the horizontal adjustment is set at 0 (Zero).
So now reading the scope the lines represent (starting at the bottom line marked) 0volts then 50volts then 100volts then 150volts then the top mark represents 200volts (all as P-P voltages). So if you have a voltage half way between the 150 and 200volts you know it is 175V P-P.
Your tube tester is know a valuable ac voltage reference in comparison to buying an expensive AC reference voltage source. Now remember this isn't rocket science, this is for the poor man radio mechanic type person. So you can use the 5 volt filament as 14Volts P-P and 10Volts as 28.2 Volts P-P.
One of the reasons for using only the Vertical line and not using the horizontal gain is that without the horizontal you can see smaller spikes that exceed the voltage are more discernible on the faint peaks as the sweep doesn't steal some of the trace to see a whole screen which makes the vertical line more visible.
You can use the voltage divider in the scope to customise the voltage ranges to suit your needs of voltages.
You can use those to set up your reference voltage, also if you have an old tube tester you could tear it apart and save the filament transformer as a multi-voltage DC power-supply.
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