A few restoration questions-- rectificiation, B+ voltage, etc

[fltyrap]

Hi Everyone,

I'm pretty new in here. I was recently given a Zenith tube radio, a C845, chassis 8C02. I have been trying to teach myself enough to get it operating safely (I have done some soldering and worked on low voltage circuits before), and have a capacitor kit here to replace the electrolytics, but I have a few remaining questions and searching the internet isn't yielding the information I need. I hope some of you guys can help a newbie get it right (and avoid killing himself). Bear with me, these are going to be some pretty basic questions!

1. How do these radios step up the voltage (B+) that is used for the tubes? The radio I have uses a selenium rectifier. I have the schematic, but I can't tell what the output voltage should be (the first voltage shown after the rectifier and a subsequent resistor is 120v, but I don't know if this should be my target, or for that matter how 115v mains on the schematic becomes 120v after rectification).

2. How do I test B+ voltage? I have an old analog multimeter-- where would I clip both leads? Guidance here would be especially appreciated, as I think this is probably the most dangerous thing I will do)

3. I have a IN40007 diode to replace the selenium, but I'm a little confused about how to know what step down resistor to use. I think I'm supposed to be able to measure the B+ voltage coming out of the diode and calculate the appropriate resistor value to get it to the appropriate level (if I could figure out what that should be). Am I on the right track here?

4. Someone from another posting on this radio recommended using a 68 ohm, 5 watt dropping resistor. The local neighborhood Radio Shack doesn't stock anything this beefy--would I need to order something like this, or can I put some power resistors in series until I get the correct B+?

Thanks in advance for any information you might have-- I would really love to get this radio running, but teaching myself tube circuits is harder than I thought!