Many moons ago; I started to work in a St. Louis trade school repairing test equipment.

After starting the job I found out there was no voltage / calibration source for the oscilliscopes.

In one of my more lucid moments I thought, lets make one.

(Switch shown in 1 volt position in drawing above.)

You need a 6.3 vac filament transformer, some perfboard, a 12 position rotary switch, something to house it, and resistors; 17 - 1k Ohm, & an 1 - 820 ohm resistor.

 
Representative filament transformer and 1 pole 12 position rotary switch.
Resistors not shown. 

Use close tolerance (1 % , or measure) and connect all resistors in series, with the 820 ohm resistor at the end.

6.3vac rms = 17.819 V. p-p, so 17 ea 1000 ohm resistors plus an 820 ohm resistor will be really close, (99.99%).

Each 1K will develop 1 volt and the 820 ohm resistor handles the rest.

You can add an on/off switch or just plug it in when you need it.

I set the circuit up for 1 thru 10 plus 15 volt taps, but you can set it up however you wish.

Have fun.

Dr. Cheap aka: KF9F