NAD: 1968 Super Reverb

[Jasonpatrick]

I got Plenty more photos from plenty more not very old amps if anyone interested

 

[Jasonpatrick]

What brand are those screen resistors? So we can be sure to anecdotally avoid those too.

It’s called a design flaw in the circuit. That fender ignores …

 

[sds1]

I got Plenty more photos from plenty more not very old amps if anyone interested

Define not very old? What's the newest manufacture date where you can show an example of premature EC fail?

 

[Jasonpatrick]

Define not very old? What's the newest manufacture date where you can show an example of premature EC fail?

Do you work for IC? Or own stock? Hahaha

 

[sds1]

Do you work for IC? Or own stock? Hahaha

No I don't. Also IC is owned by CDE. I used IC-branded caps just once in recent years, in a 30yo boutique amp that didn't leave room for anything bigger than the IC's it came with.

Otherwise I pretty much use Nichicon, Rubycon radials in all my builds.

Anyhow since you have all these examples, what's the latest manufacture date where an IC failed prior to 15 years? Just curious, thanks in advance.

 

[charlie chitlin]

Argh.....now you are reminding me of the one I let get away! Also a dripedge SR that sounded glorious (like my dripedge VR but louder!) and I quibbled about the price and it was a no so I left it. I regret it to this day. Best amp I ever heard after my 68 VR.

I remember a very fine player coming to possibly purchase my BF '66 SR with CTS alnicos.
He loved it.
Then he saw the '68 and said, "How about that one?"
He plugged it in and was blown away.
I should have said, "Not for sale."

 

[Jasonpatrick]

No I don't. Also IC is owned by CDE. I used IC-branded caps just once in recent years, in a 30yo boutique amp that didn't leave room for anything bigger than the IC's it came with.

Otherwise I pretty much use Nichicon, Rubycon radials in all my builds.

Anyhow since you have all these examples, what's the latest manufacture date where an IC failed prior to 15 years? Just curious, thanks in advance.

Ewwww you’re a radial guy?jkjk! I think the latest one that I’ve seen is 2017? 15? Was a DRRI ….Hey if quality has changed, more power to them. All it takes for me is the “ hey we had a bad batch that somehow passed quality control” for me to be like hard pass and until I start seeing/hearing about F&T having issues , that what I’ll use. Made in Germany sounds good to me.

 

[Wally]

Re: 600vdc electrolytics… no affiliation, no experience. I learned of this source on a forum.

Capacitor Shopping Cart for Tube Electronics

Capacitor Shopping Cart and Retail Price List for High Voltage Film Capacitors, Ceramic Disc, Silver Mica and Electrolytic Capacitors.

www.justradios.com

 

[Teleguy61]

Great score!
Good luck!

 

[D'tar]

IC should change the color/appearance to give the perception of a new better product!

Edit to say....
LoL!!!

 

[D'tar]

IC should change the color/ to give the perception of a new better product!

Re: 600vdc electrolytics… no affiliation, no experience. I learned of this source on a forum.

Capacitor Shopping Cart for Tube Electronics

Capacitor Shopping Cart and Retail Price List for High Voltage Film Capacitors, Ceramic Disc, Silver Mica and Electrolytic Capacitors.

www.justradios.com

I have seen but never shopped there before.... Those are amazing prices!

 

[jumpbluesdude]

Why would you suggest it be wired with the hot lead (black) going directly to the PT then fusing and switching on the neutral (white)? That contradicts anything I've ever read because it puts unfused wall current into the PT full time and should the PT short to ground hot current goes directly to the chassis. Common practice is to wire white (neutral) directly to the PT primary then fuse and switch on hot. I'm not saying you are wrong, I'd just like to know your theory here as it's opposite anything I've read.

It's also common practice to eliminate the ground switch and "death cap" entirely, which you seem to advise otherwise. As I'm a veteran of the two-prong & death cap era, where getting a jolt from an ungrounded or revered polarity microphone or one of your bandmates was a rite of passage, I'm happy to eliminate the SoBs at the first opportunity. I recall vividly a spark about six inches long jumping from a Chicago Civic Opera house mic to my lower lip and blowing me off my feet, onto my keester and into the nether regions of consiousness for a few moment afterwards. I kinda like the three prong and no death cap world as a result.

Apparently, you missed where I said the ground switch and so-called death cap are abandoned.

Basic electronics - no work is done until a circuit is completed. Voltage is potential. Ground completes the circuit.

How many Schumacher transformers have you seen short to ground. I’ve never seen it. If it does, it pops the breaker on the power side or completes the circuit, but it’s safe. What is also safe is that all the potential from the hot side is in the transformer and only exposes anyone opening the amp to voltage at one point - the transformer side of the power switch. Again, it is safe. No voltage on the fuse until it’s needed - when the circuit is intended to be completed.
Please read my post with safety in mind instead of with a desire to be contrary or superior.

 

[jumpbluesdude]

The Atoms are all over 15 years old, if it was my amp I'd just replace them while you have it open on the bench. Then you know it's been done and, barring any required service, can walk away from the amp for another 15-20 years.

I didn’t change the filter caps in my 1960 Harvard until 2015. If the part continues to work as designed, why change it? The filter caps in my 1963 Fisher 800c are still original. If the part is working as designed, use it. Do you replace tires on your car when they still have enough treads to hold the road?

 

[jumpbluesdude]

Holy Twin Sisters Batman, that's a week 21 1968 AB763 '68 Super Reverb! Probably one of the last one's made before the dreaded first gen '68 Silverpanel circuit was launched. From your photos it is a near dead ringer internally for my own week 21 '68. which I will have owned for 50 years this spring. To my somewhat informed eyes it looks very good inside, a great score for $500!

That amp has been well serviced, that's very nice looking work inside. The resistor replacements are easy to explain, beyond simply removing the hiss by swapping out the plate resistors. They used those cheap Jamaican resistors in that era and most will by now either have failed or drifted way off song. They are easy to identify, look at the three vibrato section resistors, they have that dull color. The blue Sprague Atom filter caps are correct, they used to be the go-to cap until the prices got way out of hand and techs started using the excellent German F&T brand caps. Were it mine I'd get a read on the dropping resistor values, they are the two between the positive poles of the dfilter caps. If they are original they have most likely drifted and that will throw off all the voltages downstream. Easy to replace them when doing the filter capacitors.

It would have had CTS alnico speakers originally. I'm not familiar with those Carvin speakers, but if they sound good they are good.

It should have a GZ34/5AR4 rectifier tube, which will raise the internal voltage (B+). Someone has installed the 5U4GB no doubt to drop the B+, but that does make the amp sag more and it also has a 50% greater amperage draw on the power transformer. A better solution is to use the correct rectifier tube and a "buck" transformer to reduce the line voltage going into the amp to the then common 115 - 117vac the amp was originally designed around.

Enjoy that amp! Mine was a workhorse for years, still the best amp in the house!

FYI: Using a 5U4 as a suitable substitute for 5AR4 was not done to reduce B+. It was a recommendation to technicians in a Fender issued technical bulletin. It is a less efficient rectifier, so that is the result. Per the bulletin, the 5U4 is the correct tube. Schumacher transformers are overbuilt 20% with the exception of the Princeton Reverbs. They are borderline and shouldn’t be pushed. The rest can and have handled the higher voltages put out by power plants today.

 

[charlie chitlin]

I remember a very fine player coming to possibly purchase my BF '66 SR with CTS alnicos.
He loved it.
Then he saw the '68 and said, "How about that one?"
He plugged it in and was blown away.
I should have said, "Not for sale."

As an addendum...
When I got those amps, the 66 had ceramics and the 68 had alnicos.
I swapped them because I thought it would make the 66 perfect.
The shocker was, it put the 68 over the top and made a great amp an incredible amp.

Do you replace tires on your car when they still have enough treads to hold the

Absolutely!
If they're 15+ years old, have potential to catastrophically fail and take me with them?
That's a no brainer.
This is why we replace electrolytic.
You made the perfect analogy.

 

[jumpbluesdude]

Nice amp. With the work that was done, it was a bargain, imho. @itsGiusto, the AC is not wired in the best and safest if I am seeing things correctly. The hot should go to the fuse then to the switch to connect to one end of the primary. The white neutral should go directly to the other end of the primary.

You are mistaken, Wally. Confining the voltage potential in the transformer and only exposing 1 point in the amplifier at the switch is safest.

 

[sds1]

Do you replace tires on your car when they still have enough treads to hold the road?

Great example. Tires absolutely have a limited lifetime that doesn't directly relate to the appearance of the tread.

When do you change your oil? Manufacturers recommend you to do it on a regular schedule, protectively, and without consideration of the condition of the oil or the current operating condition of the vehicle.

 

[sds1]

You made the perfect analogy.

Yeah that backfired.

 

[ETMusic777]

I've been on the lookout for a good deal on a super reverb for 2 years now, and one finally came up locally for $500. It was selling for so cheap ostensibly simply because the original tolex, back panels, grill cloth, reverb tank bag, and speakers are gone. But the amp is fully functional.

I've looked over the amp, and to my knowledge, I think it was a really good buy for this price - I see super reverbs from 1968 that have their tolex and grill cloth but without original speakers that sell for $1300 these days. And if they have the original speakers, I see them selling for $1900. However, I would love the opinions of some of the community folks who know their way around vintage amps, to see if there's something I'm overlooking about the functional condition of the amp.

I should note that for me, I don't ever buy vintage amps for the purpose of owning a vintage amp, or for resale value. I purchase amps like these when they're cheaper to buy and restore than it would be for me to build from scratch. I'm mostly interested in playing the amp, but not really interested in it as a collector's item. So it doesn't bother me in the least that the tolex and grill cloth are gone.

Here are some shots of what's inside the chassis.

View attachment 1071780
View attachment 1071782
View attachment 1071783
View attachment 1071784
View attachment 1071786

My first impression is that the lead dress on this seems pretty damn good compared to my two other silverface amps (a 1972 princeton reverb and a 1972 twin reverb). The the heaters are elevated significantly above the signal wires, wires mostly seem to try to cross each other perpendicularly, etc.

I do have some concern about some solder joints, and I'm thinking maybe I should solder-suck them, and reflow solder.
This picture shows some where maybe there isn't enough solder, and the connection looks tenuous:
View attachment 1071792

And this picture shows some where there seems like there's way too much globby solder, and the solder also looks really dull, like maybe it's a cold joint:
View attachment 1071793
I'm interested in your advice, should I leave these joints be, or preemptively try to fix them?


Interestingly, the amp has a Trainwreck Type-2 master volume installed. It's not something I'd choose to put on there myself, but I guess I might as well keep it, at least for now. It sounds fine.


The previous owner thought this might be an AA270, AA1069, or AB568, however, I do think that the circuit seems like it may have already been blackfaced to AB768 specs, or at least close. I'm glad about this, since that's something I would have done myself anyway.
In a cursory glance, I'm not seeing some of the telltale signs of the later silverface circuits. For example:
1. If there were power tube caps from grid to ground, they've already been removed. None exist now.
2. The input cap to the PI seems to be 0.001uf, not 0.01uf
3. I think it has a bias circuit, not a balance circuit like on later amps
However, the amp does seem to have a 5U4, not a GZ34, so it's not full AB768, at any rate.


The owner indicated that the amp had been recapped within the past decade, and this seems to hold up. I see sprague electrolytics, not original white fender ones. However, the original blue molded caps still seem to be there for coupling caps, which may be good, I know people tend to think highly of those.

The doghouse seems to also have what I think are spragues, based on them saying "ATOM". Can anyone confirm? I'm pretty sure these aren't original at any rate, so it's unlikely I'd need to swap them out.
View attachment 1071794


One slightly concerning thing is that there seems to be something melted on the power transformer:
View attachment 1071796

However, I didn't see any sign of this in the chassis. Maybe it got too hot at some point? Advice would be useful!


The cabinet is one that has screws to keep the baffle on, which I like! It's not one of the glued-in kinds.
View attachment 1071798


I guess for my next steps I plan to go through it and check some more values to see if it's really blackface specs, and take some voltages. I want to look at the PI plate resistor values, at least.
I'll install 1 ohm cathode resistors on the power tubes, and make sure the amp is biased right.
I also want to make back panels for it out of some plywood, and get a reverb pouch and make a cardboard bottom for the tank.
I will also remove the death cap, or at least disconnect it from the high-voltage end.



I also am going to swap the current ceramic Carvin VL10 speakers for something closer to CTS alnicos. I have 2 eminence made fender 10" blue alnico speakers from the 90s (which I hear are pretty similar to CTS), and 2 Jensen 10" alnicos. I'll put those in for now, but I may want to swap the jensens out later for something more CTS-like, if anyone has any suggestions.


I'd love to hear your thoughts! Do you think this was a good purchase, or is there something big I'm overlooking? Please let me know if you see anything that I should address in the amp, I'd like to try to spruce it up, get it in great functional shape!

Congratulations! What a fantastic deal too. Those Carvin speakers are not too bad, they are good. There was a set of 4 CTS Alnicos from the early 70s on ebay last week. I think they sold for $375 which is a good deal. They had been reconed. If you look around, you may find another set.

Another option for Super Reverbs, which is popular is the Eminence Blue Frame 1028P Alnicos. They have a paper former. The newer version is the 1028K which is kaptan former. https://eminence.com/products/legend_1028k. I have 8 of those.

I have a 67 blackface Super Reverb, with an August, 1967 tube chart and serial number A25845. Ive been looking but I have not seen any photos of any blackface Super Reverb that shipped later than August, 67 or has a higher serial number that this one. I dont think any BFSRs shipped later than August. Curiously Ive seen a few silverface Super Reverbs with July, 1967 tube charts and lower serial numbers than mine, so they were obviously clearing out the last of the BF parts in August 67.

 

[JRapp]

BTW---I would also replace those cheap molded RCA reverb cables with the proper braided types.