NAD Quad Reverb and restoration thread

wagdog

wagdog

Ack
I love old silverface fenders. I Picked up this well used Quad Reverb today. I believe it's an '74, but I'm not certain. Still working on the date.

The cab is pretty beat up, but salvageable. Not sure I really want a 4x12 Fender amp. I do have a Fender 2x12 cab with a twin reverb project amp in it that I could use, or I might have a head cabinet built... or I might restore the 4x12.

The amp worked but had pitiful volume and was pretty thin. No reverb heard. I haven't checked the tank yet, I suspect it's the cables. It had three diffreent 6L6s in it and various 12ax7s - all of the tubes were old.

The takedown was rough. The chassis screws are pretty well pooched. Once apart, the innards looked like I'd expected. Once the doghouse cover came off, the reason for the lack of volume out of the amp is apparent. I'll be ordering parts over the next few weeks and patching it up. I'm also going to remove the ground switch and install a real adjustable bias as opposed to the balance pot. I'll probably covert the PI and power amp to a blackface circuit as well.

Here's the pics....











 
Yeah, those caps look rough. That will be awesome when you get it fixed up.

I had a beat up Musicmaster amp and found a guy to build me a cab to convert it to a head.
 
Psychotronic said:
Had one of those in high school. Twas a piece of shit. Hopefully yours is better than mine.
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It'll work out 'cause I know how to fix/restore it. I like silverface fenders, so it should work out.

What went wrong with yours (and what year was it)?
 
Chad said:
Yeah, those caps look rough. That will be awesome when you get it fixed up.

I had a beat up Musicmaster amp and found a guy to build me a cab to convert it to a head.
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The caps and a retube should bring it back it back to life.

The other stuff (blackface circuit, bias) should help as well.

I just measured and the chasis is a perfect fit into my other fender cab (super twin reverb 2x12 cab). I may go that route at first - that cab has some new'ish jensen speakers in it.
 
I see the problem... There was a kitty in the speaker bay. Try de-cat-ing it before you go through the trouble of the re-capping, re-tubing, and blackfacing it.
 
wagdog said:
What went wrong with yours (and what year was it)?
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Ah, we were just kids, we had no clue what year it was or how to make it sound better. I just remember it weighed a ton and sounded like dogshit. I do remember the next guy who owned it left it in somebody's backyard after a gig for weeks, where it got rained on a few times and God knows what else. That was the last we'd heard or seen of it. That would've been somewhere around '87 or '88.
 
RyanNo3 said:
I see the problem... There was a kitty in the speaker bay. Try de-cat-ing it before you go through the trouble of the re-capping, re-tubing, and blackfacing it.
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You have to add cats if you want it to purr.

Spent a little time messing around with it tonight.

I've got a shopping cart of stuff going at tubedepot. Going to sit on it over the weekend. I think I already have all the components to blackface it, but I do need the bias pot and definitely need the filter caps. Tubedepot is out of stock on the F&T 22uf 500v caps, so I'm probably going to get Illinois caps - not real happy about that, but they'll probably be fine.

Just going to double check everything and order on Monday.

Put in a known set of working, but old tubes to test with.

Got the reverb working. Someone had done some creative wiring inside the tank apparently.

It appears that 2 of the 4 12" speakers are not working. This is kind of a good thing as it makes the decision as to what to do with the amp a little easier. I ran it through the 2x 2x12 jensen speakers from my old twin project amp - sounded really good.

I'm either going to mount it in that cab -or-

Cut the 4x12 cab apart and make a head cab out of it and make a 2x12 cab out of it. I'm kind of leaning in this direction because I really have no need or desire to own a combo with a 4x12.
 
Ordered the parts today.

Will recap first and see where it's at before adding a bias adjustment and blackface PI - no need to mess with it if it sounds good after getting new caps.
 
Is there a clean-looking cap anywhere in the amp?.. those coupling caps look like they are melting, I can't tell if someone added silicone caulking to the top of the caps or they are coming apart. That .02 cap coming of of V2B plate actually seems to look a hot wire/iron burned right down the top of it.
 
Wyatt said:
Is there a clean-looking cap anywhere in the amp?.. those coupling caps look like they are melting, I can't tell if someone added silicone caulking to the top of the caps or they are coming apart. That .02 cap coming of of V2B plate actually seems to look a hot wire/iron burned right down the top of it.
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I see what you're saying Wyatt, but the coupling caps are fine, not melted. All of the caps seem have been dipped in some kind of waxy substance and dried upside down. Some of them have bubbles of it on top where it drooped before drying. I've seen that before in silverface amps - there is also some of it on the boards.
 
wagdog said:
I see what you're saying Wyatt, but the coupling caps are fine, not melted. All of the caps seem have been dipped in some kind of waxy substance and dried upside down. Some of them have bubbles of it on top where it drooped before drying. I've seen that before in silverface amps - there is also some of it on the boards.
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That's why it looked weird. I'm used modern builders securing things with silicone, but that wax looks a little more "organic."
 
mongooz said:
those things are L O U D !!!!!
(virtually a Showman combo)
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The same chassis as the Twin Reverb.

Twin Reverb=2x12
Vibrosonic Reverb=1x15 (I think this would be my fav)
Quad Reverb=4x12
Super Six Reverb=6x10
Dual Showman Reverb=head

Eventually, the schematics in the '70's just covered them all with two different OT part numbers (Vibrosonic was 8 ohm, the rest 4-ohm) and a slew of speaker wiring diagrams.

Of course, the Quad and Super Six were heavy as sin, keeping resale low, and I bet many ended up in landfills because people couldn't ind buyers. But tone-wise? They were everything the others were.
 
@Wyatt - curious if you would share your thoughts on:

1. Replacing the bias balance with a fixed (adjustable) bias? I could keep the bias balance and just add an adjustable pot to adjust overall bias, leaving the silverface bias circuit.

2. Changing the PI configuration to a blackface (ab763) circuit?

Both of these are easy enough to undo I suppose, but if neither is going to make a huge sonic difference I don't think I'll bother.
 
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