3 prong cord for my '64 Gibson GA-40T

[jaymann]

Hi everyone.
I've been lurking here for quite awhile gathering helpful info, but it's time I need help.
I've got a '64 Gibson GA40T (not the earlier tweed, the Crestline series) that I want to add a 3 prong ac cord to.
I've done the same operation on my older Fender amps thanks to a wealth of info I could find, but can't find info on doing it to this amp.

Looking at the amp, I'm guessing that I want to somehow wire the fuse to the hot side, and get rid of the death cap. The rotary power switch with 2 ground positions has me confused though.
On the Fender,iirc the ground switch is bypassed. But being that it's separate from the power switch it's easier to get my head around.
Here's a pic
http://www.iwannarock.ca/ga40t.html

I found the schematic for it here:
http://music-electronics-forum.com/atta ... ematic.jpg

I'd appreciate anyone who can give advice on the right way to wire this.

[martin manning]

Ground clip... that's a new one! This looks pretty straight-forward. Clip out the death cap, run the hot (black) wire to the fuse holder, run the white to S1B (to the other side of the PT primary), and put the green (safety ground) on a dedicated bolt through the chassis.

[jaymann]

Ground clip... that's a new one! This looks pretty straight-forward. Clip out the death cap, run the hot (black) wire to the fuse holder, run the white to S1B (to the other side of the PT primary), and put the green (safety ground) on a dedicated bolt through the chassis.

Wow, thanks for the speedy reply.

so just so I'm clear, I basically switch hot and neutral around (black for white in my picture) clip out the cap and add the green ground?
Or have I missed something?
http://www.iwannarock.ca/ga40t.html

[martin manning]

Hang on, the picture doesn't appear to match the schematic. My mistake for not checking first. Can you post another picture or two of that area? And can you identify which leads are the transformer primary? I'm thinking the black tubular cap is the one that goes to ground, is that right?

[jaymann]

Hang on, the picture doesn't appear to match the schematic. My mistake for not checking first. Can you post another picture or two of that area? And can you identify which leads are the transformer primary? I'm thinking the black tubular cap is the one that goes to ground, is that right?

Black cap does go to chassis ground.
It's entirely possible that someone's already messed with it. Someone did a butcher cap job and there's electrical tape and extra wire everywhere.
I'll post some pics in a couple minutes.

[jaymann]

http://www.iwannarock.ca/ga40tb.html

does this help?
Black cloth wires go from PT to side of fuse and 2 switch.
Green Cloth wires go from PT to jewel light.

[Phil_S]

Save the black beauty cap. These have value if not leaky. Check eBait.

Remove the old line cord. Get a proper strain relief bushing for a 3 wire cord. The old one is too small. You may have to carefully enlarge the hole.

Get a three wire line cord with a pig tail and molded plug. I buy cheap extension cords at Target and clip the end I don't need. Or find an unused IEC cord in the computer supply room at the IT department if you work in an office environment. They will have a pile of them.

The black wire in the line cord goes to the fuse. The fuse goes to the switch. The other side of the switch goes to one of the PT primary wires (black).

The white wire in the line cord goes directly to the other PT primary black wire.

The green ground wire in the line cord gets soldered to a ring lug. The lug gets bolted to a dedicated ground bolt through the chassis. You may need to drill a hole for it if you can't find an unused one. There should be more slack on the ground wire than other wires. In case of a catastrophe, it should be the last wire to experience a pull. No spade lugs, as they can slip off the bolt.

The present fuse holder wiring looks funky to me. In the end, only two wires go there -- the line cord and the connection to the switch.

The lamp seems to be a 6.3V lamp. It is not part of this job. The green wires are the 6.3V supply from the PT secondary.

[martin manning]

I think this will do it. Once wired up this way I suggest putting a multimeter set to measure ohms across the AC line and neutral, and cycling the power switch through all its positions. You should see infinite resistance (open circuit) in the off position and the resistance of the PT primary on all other settings. Also check that neither side has continuity to ground in any switch position. You'll have to find a spot to attach the safety ground to the chassis, preferably on its own dedicated screw.

[jaymann]

thank you for the picture. after a long day it sure helps!

I guess it goes without saying that the Cap gets snipped out as well right?

BTW, is there a vendor of Electrolytics that anyone can recommend.
The one place I normally deal with has a $50 min order.
Not worth ordering $50 worth of stuff for four 10uf 450V and two 20uf 450V caps!

[ampdoc1]

I use Antique Electronics a lot. I think you have to submit a company name to get an account, but pretty much all that requires is an address. If I remember correctly, they don't require business license, etc.

I usually get parts in about 3-4 days, and they don't have a minimum order policy. Also, they have a VERY broad selection of parts at reasonable prices.

[martin manning]

Yes it's best to remove the cap going to ground.

Antique Electronic Supply does have a very good selection of electrolytic caps for vintage gear, including some multi-section types. They sell retail too, with no minimum order.

[jaymann]

thanks for the tip about Antique Electronic Supply.
I've been using CE distribution. Prices are a little less , but $50 min order and high shipping rate is a killer.
Time to find some Caps!
It looks like this amp used to have a multi-stage cap.
Someone installed Sprague Atom 10/10 450V axial , but I can't find those.
I could clean up the whole mess with two 20/10/10 450V Cans, but it's way cheaper to just order some new Axials.

Thanks for all the civilized help!

[Phil_S]

If you can find a safe and appropriate way to mount individual caps, there is no need to get the expensive cans. You may need to install a small terminal strip or two. What's wrong with what's in there now? Is it really a hack job? Show us a picture.

[jaymann]

If you can find a safe and appropriate way to mount individual caps, there is no need to get the expensive cans. You may need to install a small terminal strip or two. What's wrong with what's in there now? Is it really a hack job? Show us a picture.

the amp started to hum. upon inspection, a couple of the caps are bulging out the side.
There's also too much wire and electrical tape for my tastes.
http://www.iwannarock.ca/ga40tcaps.html

[Phil_S]

Oh, that's fugly. I don't think anyone here will disagree with you on the tape and the caps. Tape had no place in there. Ewwww.