need help changing from 2 to 3 prong Grounded cable for univox u45b project

[darrellcheng]

Hello, I am restoring a u45b and I want to solder a grounded cable. Where do i solder the ground from the wire? Also, I am replacing the caps and the tubes and cleaning out the scratchy pots. do i need to bias the tubes? I am hoping that by doing these things The amp will be back in working condition. I've read that the transformer can also be the source of a nonworking amp. How can i tell if it is leaking or if its the problem? this is my first time working on an amp.
Thanks for all your time!

[Regis]

The power tranformer should be in the same area the power cord enters the chassis, loosen one of the nuts and put a solder lug under it to attach the ground lead. It's a good idea to take a little sandpaper to brighten the metal up under it to get a good connection.

That amp is cathode biased, you don't need to bias the power tube.

[Brad1]

That's a good start to change that. I also have a U45B. It's a little screamer dimed! You can almost get it sounding like a baby Marshall. Back off just a tad off "10", and it gets good early-Stones crunch.

In case you need schematics, (and also a there's a forum), go here:

http://www.univox.org/

You say it's your first amp repair. I hope you've read the safety procedures, and are following them? #1 thing is don't touch anything grounded (amp chassis, metal workbench, etc) with one hand while you're fingers and knuckles and wrist of the other are poking around inside a live amp. Inevitably, you WILL touch something hot...especially if you ignore the rules. Also, read up on how to discharge caps.

Make sure the white wire goes to the switch/fuse, the black goes to the other, and do as Regis suggested and put a lug on the ground and tighten the nearest transformer nut down around it. (You can even flow some solder down into the wire/lug after crimping the lug on, if you wish. You'll have a hard time trying to solder a wire to a ground spot unless you have a high wattage iron, and a lug will hold better anyway.)

Don't make the wires any longer than needed, but leave a bit of slack. Leave about an inch or so of the unstripped cord casing inside the amp so you can tighten up a nylon zip tie against the inside chassis to keep the cord from pulling out.
And make sure there is a rubber grommet in the cord hole around the cord. NEVER leave a cord rubbing bare metal.

You didn't exactly mention why you questioned the transformer. What is the amp doing, (or not doing) that caused a transformer question?

Brad1

[darrellcheng]

Thank you for your help guys!
Yes this is my first attempt and I have read and will continue to read up on safety procedures.
Regarding the transformer, I'm only questioning it because it seems to be a common problem, after I finish with the caps and tubes, if the amp still doesnt work, thats my next logical step.
Thanks for the tip on discharging caps, just read up on it.

[Randall]

Make sure the white wire goes to the switch/fuse, the black goes to the other,

Wouldn't that be switching the neutral? Isn't the opposite what we'd want?

[Jazz P Bass]

Yeah, bad advise for sure.
Black (hot) wire to the fuse & then the switch.