NAD '68 J-12

[charliea]

This is my first tube amp, and I bought it sight unseen from a GC in Kentucky, where they could give me about zero details. Man, did I get lucky. It's a '68 (per the serial #) J-12 with no A or D after it which means, miracle of miracles, that it uses two 12AX7s and two 7591s, instead of some of those crazy tubes like 6BK11 that Ampeg once used. The controls couldn't be simpler, and it sounds like a dream. Starts crunching a little before half volume, and just sings as you turn it up. For lower volume I can plug it in the "bright" vs "normal" jack and save my ears. Has a CTS 12" that looks good and sounds great. The tremolo is a little overpowering. Don't know if it's right or not, as I've never had one before. No subtlety to it at all. The 7591s are Ampeg branded, maybe original, the 12AX7s are some German numbers, replacements, I guess. In any case, it sounds so much better with electric guitars than my old Carlsbro solid-state acoustic, I'm grinning from ear to ear. I opened the back and had to vacuum the dust out to see what was happening. Hadn't been opened in a long, long time. Here's some pics, before the tubes were inserted, of the front, control panel, back with cover removed, label and, last but not least, the two-prong supplied on-off switch with what I presume is the "death cap", which I need to fix pretty quick.

Charlie

 

[Default]

Re: NAD '69 J-12

Congratz! That's a clean machine brother! :mrgreen:

 

[Jeff Haddad]

Re: NAD '69 J-12

Nice score! Those preamp tubes could be good ones, too.

 

[Bill Ashton]

Nice! Though, so we can continue to get your great posts, you will of course be installing a three-prong cord/plug and removing the "death cap," right? :wink:

 

[charliea]

Nice! Though, so we can continue to get your great posts, you will of course be installing a three-prong cord/plug and removing the "death cap," right? :wink:

I installed a 3-prong plug with two wires soldered to the switch, the ground through a ring terminal to a chassis bolt, but didn't mess with the Cap of Death. Maybe I should. Just don't know. The nice thing about the 3-prong is that it did away with the hum, which otherwise required grounding the strings. My X170 with the WCR PAFs sounds fabulous through this amp. Wish I knew how to play it. Some day. Right now I'm working on Mr. Blue, which is the kind of thing I got the guitar and amp for, and the music is so good it makes up for a lot of my mistakes.

 

[Bill Ashton]

I cannot find Dr Spots diagram right now, but here is how it should be off the top of my head...

Black wire goes to the bottom (tip) of the fuse holder, then to one pole of the switch, then to one lead of the transformer...

White wire goes directly to the remaining lead on the transformer...

Green wire gets soldered to a connector and then goes under the screw holding one foot of the transformer (preferably) for ground.

Steve, help me out here if I messed it up...will post the diagram as soon as I find it.

The yellow cap around the switch goes away (the death cap), so named because with a two wire plug, you have a 50% chance of inserting the neutral into the hot leg of the wall plug, and should you get just the right fault in the amp, you get wall voltage and current on the chassis...ZZZAAAAAPPPP! :shock: :shock: :shock:

The hot coming from the wall goes to the tip of the fuse holder, so the if you are extracting a fuse, you cannot accidently brush against the hot, should the fuse contact the outside of the channel.

Any electrician will tell you, "ya never break the neutral," hence the white goes directly to the transformer.

The ground is pretty self evident, hopefully with a good star washer digging it into the chassis metal.

With the death cap in place, you may trip a ground fault interupter (GFI) if you happen to plug into an outlet protected by same, as the device sees the two legs of power unbalanced and trips...happened to me on my newly capped Guild 66-J and I could not figure out what was going on...until one wiser than I showed me :wink: The person who recapped the amp had also put a new cap in for the death cap. Said cap was really good as a tone control in a Telecaster I was working over

 

[Default]

Cut the cap out now! The only thing it adds to the amp is a short to ground when it fails. ;-)

 

[Bill Ashton]

The diagrams on the left hand side may be confusing, as they are suppose to address a "Blackface" Fender I think, with the convenience outlet...go by the schematic on the right hand side:

 

[charliea]

Oops! I remember now. Black to the switch, white to the fuse holder, neutral to chassis ground is what I did. I'll go ahead and snip the End of the Universe and Death to All Mankind cap, just to be on the safe side. Thanks, guys!

 

[Bill Ashton]

Looked like you have a multi-pole switch for the off/on that is really not needed, but thats OK.
Fuse and switch should be on the same leg, with fuse first...white goes straight to one primary leg of the transformer.

Have fun and be careful!