NAD: 1968 Super Reverb

[Jasonpatrick]

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

Why would you be working in an amp that’s still plugged in if safety is your priority. I mean I know why you would, but if that’s the case, then I would assume the person is paying attention at that point. One point or three points they all zap points in close proximity lol. I wire hot to the fuse tip. Rather have hot on the fuse then on the transformer imho


To add, those zap points are not the zap points I care about. It’s the other zap points of DC that I’m more focused on haha

 

[itsGiusto]

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.

What do you think about the paper vs the kaptan formers?

I have two fender blue frames from the 90s which (correct me if I'm wrong), I think are supposed to be equivalent to the eminence Blue Frame 1028 Alnicos (not sure if they're paper or kaptan). I plan on putting those in the super reverb.

Am I correct? Are they similar to CTSs, and equivalent to Eminence Blue Frame 1028s?

 

[telel6s]

I can't help you with any of the tech stuff, but a working SR chassis for $500 sounds like a deal to me. If you have the place to crank it, Crank It! Otherwise, they still sound beautiful at 2.5 on the volume.

When I got my '72 (non-master volume), only two of the speakers were original. I replaced the other two with a pair of those same Carvin speakers. Obviously not your typical SR speaker, but they did a good job (as they also did for a while in a 2x10 cab for a Carmen Ghia head).

Have fun with the amp. My glued-in speaker baffle started getting some cracks so I built a pine 1x12 cabinet. I use a 12" 4 ohm Weber Blue Dog ceramic speaker and a Weber 4 ohm load dump. The resulting 2 ohm load makes the transformer happy and I can nudge the volume up a little farther. It's not much lighter than when in its 4x10 cabinet (I've never weighed either config) but the shorter height makes it easier to pick up and carry.

 

[Jasonpatrick]

If y

What do you think about the paper vs the kaptan formers?

I have two fender blue frames from the 90s which (correct me if I'm wrong), I think are supposed to be equivalent to the eminence Blue Frame 1028 Alnicos (not sure if they're paper or kaptan). I plan on putting those in the super reverb.
View attachment 1072348
Am I correct? Are they similar to CTSs, and equivalent to Eminence Blue Frame 1028s?

If you can find the Emmince blue frames from the 90s go for em in the super. 2nd would be two Weber 12a whatever alnico and two of the same in ceramic and call it a day

 

[ETMusic777]

What do you think about the paper vs the kaptan formers?

I have two fender blue frames from the 90s which (correct me if I'm wrong), I think are supposed to be equivalent to the eminence Blue Frame 1028 Alnicos (not sure if they're paper or kaptan). I plan on putting those in the super reverb.
View attachment 1072348
Am I correct? Are they similar to CTSs, and equivalent to Eminence Blue Frame 1028s?

I tested a set of 4 1028Ps vs. original 1967 CTS Alnicos. They were both very close, however the 1028s have a touch more midrange than the CTS. The CTS are maybe more "pristine" if that makes sense, but they are very close and both are great in a Super Reverb.

 

[SoK66]

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.

I am reading with safety in maind, and no, I didn't miss that the ground switch and death cap were out of the circuit. I asked the question because what you are suggesting be done is contrary to common practice, I.E., fusing and switching on the hot side with neutral, not hot, affixed to the primary. Again, if the transformer shorts to ground the positive current shorts to ground and to the guitar if one is plugged in. Matters not if we've seen a Schumacher short, safe practices work on potential fails. Depending upon the circuit breaker in a club to operate to code? I think I'll pass.

 

[SoK66]

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.

The original spec on the '68 SR was GZ34, per the AB763 circuit which is what the OP has. The later AB568 "Silverface" circuit spec'd the 5U4GB. Refer to the two schematics for reference. Due to today's higher line voltages vs when the amps were designed and manufactured it is common practice to replace GZ34s in AB763 amps with 5U4s to drop the B+ about 20 - 25vdc. A better method is to retain the spec rectifier and put a buck transformer upstream to drop the line voltage going into the amp to the original levels. Brown Box, Carl Hartmann's "Tone Preserver", a Variac, etc. gets the job done.

 

[SoK66]

It won't be an AB763, the only SF amps that were had the drip edge and were very very early silverfaces. It very well might have had an AB763 tube chart because apparently they made thousands of those and used them for quite some time after the other circuits were introduced.
Some possibilities are the AB568, AB569, AA1069, AA270, AA1070 and probably a few more.
With that screwed in baffle and old logo it's no later than about 72 or so. So you have blackface cab bragging rights!
By the way those CTS alnicos are toxic waste, but being the nice guy I am I offer a free disposal service. (in my SFSR)

Not quite, in the schematic B+ should be 465. So, within 20%, but not quite exact.


That's what's weird though, the voltage isn't lower downstream, it's higher than I expected, 270 on the preamp plates. Given that B+ is low, I'd expect that preamp plate voltage to be low, too, but it's not.


So do you think I can try putting in a gz34, then? Would it be safe? What plate voltage on the preamp tubes would be too high?

I'd try a GZ34 and see how it sounds. If you like it better then bias for it and party on. For mine I use a GZ34 but use a buck transformer to drop the line voltage to 115-117 depending upon how the electric company feels that day. If you like it with the 5U4 no worries.

 

[SoK66]

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.

AB763 Super Reverbs were made until mid-May of 1968. Look at the inspection stamp on nthe OPs chassis and the one I included in my first response. Both are AB763 and both inspected the same week of '68. Since 1973 I've owned mine, with a 21st week '68 inspection stamp. The fellow I got it from, bought ut new when he returned from Vietnam in '68 and had barely used it, so it was never converted, etc. until I recapped it for the first time in the 1990s. As I mentioned in my first comment to the OP, our two amps may have been built by the same tech. Mine is a drip edge as well.

 

[ETMusic777]

AB763 Super Reverbs were made until mid-May of 1968. Look at the inspection stamp on nthe OPs chassis and the one I included in my first response. Both are AB763 and both inspected the same week of '68. Since 1973 I've owned mine, with a 21st week '68 inspection stamp. The fellow I got it from, bought ut new when he returned from Vietnam in '68 and had barely used it, so it was never converted, etc. until I recapped it for the first time in the 1990s. As I mentioned in my first comment to the OP, our two amps may have been built by the same tech. Mine is a drip edge as well.

In my post, I wrote "blackface" or "black panel" as some like to call them, Super Reverbs. I have never seen a BF with a post August, 1967 tube chart. I was not referring to Silverface / Drip Edge AB763 which as you stated, were shipping well in to 1968. I don't know what the debate is here over what I wrote. People are too quick to jump on others here to "correct them" apparently. I don't claim to be any sort of expert, but I have looked at dozens of "blackface" SRs that had tube charts in 1967 (letter Q) online which is where I got the info.

 

[itsGiusto]

Absolutely. But with like 5 choices of axial caps remaining for legacy applications, and some of those being ridiculously expensive, it seems like a shame to rule one of those choices out based on a false premise.

I was wondering, actually, have you ever used MOD caps? I just discovered them, like yesterday, and they seem pretty cheap, and rated to 105 Celsius! I don't know anything about their caps and if they're good, but I do trust the quality of their reverb tanks, so maybe the caps are good?

 

[SoK66]

I was wondering, actually, have you ever used MOD caps? I just discovered them, like yesterday, and they seem pretty cheap, and rated to 105 Celsius! I don't know anything about their caps and if they're good, but I do trust the quality of their reverb tanks, so maybe the caps are good?

I haven't used them but one of the more respected Youtube techs has just switched to them. He was previously usxing F&Ts exclusively for the filter caps.

 

[SoK66]

In my post, I wrote "blackface" or "black panel" as some like to call them, Super Reverbs. I have never seen a BF with a post August, 1967 tube chart. I was not referring to Silverface / Drip Edge AB763 which as you stated, were shipping well in to 1968. I don't know what the debate is here over what I wrote. People are too quick to jump on others here to "correct them" apparently. I don't claim to be any sort of expert, but I have looked at dozens of "blackface" SRs that had tube charts in 1967 (letter Q) online which is where I got the info.

My apologies, I thought you meant you'd never seen an AB763 later than 1967.

 

[itsGiusto]

I haven't used them but one of the more respected Youtube techs has just switched to them. He was previously usxing F&Ts exclusively for the filter caps.

Which tech?

 

[itsGiusto]

They are just so great tone wise. None better. Wish I hadn't sold my perfect 66 several years ago. I have a cab and a tranny or two here, I may put together a "Super Rev-parts-verb" at some point... But trying to resist!

Get 'er tolexed and some good grill cloth for it!

So, I mentioned I'd put up a picture. Behold!

Honestly, I think it's kinda cool looking, besides that white stain on the grille cloth. I have no immediate plans to change anything cosmetically, but I won't rule anything out long-term. Grille cloth would be easy to do, but I'm less certain about tolex, specifically because the previous owner put some sort of clear finish on the wood. If I had to sand it all off, then screw it. I hate sanding.

 

[Jowes_84]

I’m a Little jealous. Like that natural look, would look great with a different grille cloth. Check out the deluxe version Rivera Amps from the 80s, … reminds me of those.
Edit-pics

 

[jumpbluesdude]

Why would you be working in an amp that’s still plugged in if safety is your priority. I mean I know why you would, but if that’s the case, then I would assume the person is paying attention at that point. One point or three points they all zap points in close proximity lol. I wire hot to the fuse tip. Rather have hot on the fuse then on the transformer imho


To add, those zap points are not the zap points I care about. It’s the other zap points of DC that I’m more focused on haha

Bleed resistors in every Fender. I’m not going to be teaching classes. You don’t don’t make something safer for people who know what they’re doing. That’s why it’s called fool-proofing.

 

[Jasonpatrick]

…

 

[Jasonpatrick]

Bleed resistors in every Fender. I’m not going to be teaching classes. You don’t don’t make something safer for people who know what they’re doing. That’s why it’s called fool-proofing.

Yeah, I’ll still pass on the line of logic that has someone not wiring the hot to the fuse. …

 

[SoK66]

Which tech?

Lyle Caldwell, Psionic Audio. If you haven't seen his videos on amp service & repair they are worth the time.