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3 prong AC plug for old Fender amp

5/31/2000 2:26 AM
3 prong AC plug for old Fender amp
I've been shocked a few times using my SF Fender Priceton Reverb. (You know when setting up at a gig & the PA's power is runnign in the opposit direction.) I want to install a 3 prong plug, thinking that it'll be the end of me getting zapped - at least from getting the ground switch wrong.  
I went & bought an 8' cable at Home Depot. It looks easy enough to install, but I already have this history of getting electricuted, so this makes me a little nervous.  
I just wanted to know if this process has been documented some where.  
5/31/2000 9:10 AM

David Funk's workbook has a good section on re-wiring the AC side.  
Book Of The Day The Ultimate Tone, Volume III by Kevin O'Connor
Have you ever wondered if there is a better way to build a Bassman, Champ, Plexi, an 800, AC-30, Bulldog or Portaflex? Or you wanted to build an SVT with off-the-shelf parts? How about a master-volume amp that doesn’t change tone with the master setting? Everything you need to know is right here, including: proper grounding techniques, wiring methods, and mechanical considerations. Eighteen chapters cover the “iconic” amps everyone knows and loves, with schematics and layouts for each, along with the technical history of the product. Eyelet-board and chassis-mounted tube socket construction is used throughout, for easy servicing and modding. TUT3 is very accessible even if you cannot fully read a schematic and is a "must have" if you are going to build an amp for your self.

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5/31/2000 1:54 PM

Great! Thanks,  
Where can I find it? (David Funk's Workbook)
6/7/2000 11:22 AM

You can get it directly from Dave Funk at Thunderfunk Labs inc. P.O. Box 740, Waukegan, IL 60085. (847) 263-7400, Fax (847) 244-1455. You might want to get it from Antique Electronic Supply if you need it fast. I had to leave several messages before he got back to me. Great book for a beginner. Yossarian.
6/7/2000 4:07 PM
J Epstein

Green wire : solder a ring terminal to the end. Bolt securely to chassis using its own steel bolt and a shakeproof (star) washer. Scrape chassis clean at bolt location before installing, to ensure good contact. Install a good strong strain relief on the cord to prevent it from pulling out. At the very least, tie a knot in the cord inside the chassis. Leave the green wire the one with the most slack, so if the cord does get pulled out, the other leads rip out first.  
Instead of its own bolt you may alternatively use one of the power transformer mounting bolts, but the dedicated bolt is preferable as long as you are willing to drill a new hole.  
Black wire : first to the fuse, then the fuse connects to the power switch, then the power switch connects to the power transformer.  
White wire : connect to the remaining power transformer primary (the power transformer primaries are probably two black wires, they will have been connected to the old two-wire AC input circuit.)  
With you new cord disconnected from the wall, verify that there is no continuity between the black or white wires and the chassis. Verify that the resistance betwen the black and white wires is >0, maybe 200 ohms or so. Verify that the resistance between the ground prong on your power cord at the wall end and the chassis is *very* *very* low - ideally less than 1 ohm (first see what your meter reads when you short the two probes together, this is often not equal to zero ohms. Then make sure your ground wire measures less than one ohm more than that reading.)  
Do not connect to the old death cap and ground lift switch connections, just leave them in there for future collectors who may want to be electrocuted.  
Plug her in and let her rip.  
6/8/2000 2:55 PM
Re: 3 prong AC plug for old Fender amp: addition
And, I'd like to add "again", make sure the green grounded wire on your new power cord is the longest one of the three so it is the LAST wire to break off if the power cord gets yanked out.  
That way the chassis is still grounded if the 120v black comes off and is rattling around in the chassis,... the main circuit breaker (or fuse) the wall outlet is using, will pop open and save you from a shock.  
"Do not connect to the old death cap and ground lift switch connections, just leave them in there for future collectors who may want to be electrocuted."
Regardless of the merits using a grounded three wire power cord, putting the fuse in the right order in old amps, or whether or not the grounding cap is needed-desired, I'm constantly reading on the internet comment-warnings about disconnecting the grounding "death cap" in early Fender BF and SF amps .  
I've NEVER run across a bad or shorted ground cap in any old BF or SF Fender.  
Have I been really lucky or is this just another urban legend folk story?  
I get the feeling that, like MANY other things I've read on the internet, many folks keep retelling this warning because they keep hearing it, not because they've ever experienced it.  
Please be truthfull!  
How many of you have actually found a bad ground cap in an old Fender BF or SF amp.  
For that matter how many of you have first hand info on anyone being electrocuted by something like this or electrocuted by any tube guitar amp?  
With that said, is there a reason to keep the cap in there if you use a proper grounded power cord chassis combination?  
6/8/2000 6:39 PM
"With that said, is there a reason to keep the cap in there if you use a proper grounded power cord chassis combination?"
It's what the logic design guys call a "don't care".  
As long as it doesn't fail, it doesn't matter much.
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