I agree with those who suggest a digital Volt-Ohm meter. Here is a link to those at Radio Shack (since you mentioned them).
Multimeter
The little yellow multimeter with the giant display looks easy to use and is only $19.95. I would not be afraid to use it to bias my tube amps.
Multimeter
The little yellow multimeter with the giant display looks easy to use and is only $19.95. I would not be afraid to use it to bias my tube amps.