Do Vintage Fender amps (AB763 type, etc.) all use the same reverb tank?

[Tom Phillips]

...Sometimes if they don't sound right, not enough in the high or low frequencies, I'll modify them by either stretching a coil on the loosest spring (to add lower echo) or snipping a couple of coils off the tightest spring (to add higher echo). I did ruin a tank on my first attempt at this but it was a lousy sounding tank anyway so there was nothing to lose. I learned that the adjustments had to be smaller than what I did that first time. But it can work if you're judicious and careful.

That's very interesting. Many of the tanks have seen had a dot of what looks like epoxy glue added where the spring is attached to the transducer. (The original Gibbs tanks did not use the glue.) I'm curious how you dealt with that when you snipped coils off.

[Chuck H]

That's very interesting. Many of the tanks have seen had a dot of what looks like epoxy glue added where the spring is attached to the transducer. (The original Gibbs tanks did not use the glue.) I'm curious how you dealt with that when you snipped coils off.

I didn't remove the adhesive. I carefully snipped the spring and used a needle nose to bend and curl hooks for rejoining. This is where the "judicious" part comes in because the effort is to make a very slightly tighter spring even with this deformation.

[Helmholtz]

I carefully snipped the spring and used a needle nose to bend and curl hooks for rejoining.

So you're adding another spring joint, making it 3 springs in a string?

[Mick Bailey]

Sometimes a poor sounding tank can be improved by paralleling a cap across the output transducer to give a resonant peak. Cascade did this quite often with their 2-spring short trays that had the diagonal linkage and removing the cap makes the tray sound dull.

[Helmholtz]

A 2.2n "resonance cap" can be found in many Fender SF amps

[Chuck H]

So you're adding another spring joint, making it 3 springs in a string?

No. Not really. The spring is snipped only a couple of turns beyond the transducer joint. There's no significant spring length with the new hooked joint to qualify another springs contribution. Just to reiterate... The goal is to change the tensions slightly. The first time I attempted this my adjustments were too large and (seemed to) put the springs, loosened or tightened, outside the useful range. On that note...

The best tanks have collaborating repeats that are barely audible. If that makes sense.?. The worst seem to either have audible repeats or everything is just smeared together like white noise. I think Accutronics really had it figured out back when they were the premier offering. But new tanks, made with different materials and metallurgy for the springs made by different manufacturers always seem to miss the mark set by the Accutronics company decades ago. But things have changed and I don't think we'll ever see a company making spring reverb tanks to the same quality marker. The technologies are just different now and there's not enough profit in recreating that quality. Even though there is still a profit to be made by offering similar construction. There's a difference.

[Helmholtz]

What about the tanks Fender currently uses?
The Accutronics tank in my '90s Vibroverb RI sounds very good - no significant difference to the Hammond tank in my BF SR.

I often wonder if current production tanks use the correct magnet pole orientation as described in the Hammond patent.
Pole orientation affects transducer sensitivity and linearity. If wrong, output may be low and distorted (frequency doubling).

[Chuck H]

I often wonder if current production tanks use the correct magnet pole orientation as described in the Hammond patent.
Pole orientation affects transducer sensitivity and linearity. If wrong, output may be low and distorted (frequency doubling).

I never noticed anything like this. All the tanks I've tried seem to be clear and respond predictably as expected to the circuit. What I HAVE noticed is reverbs that sound more unnatural. Like a spring is bouncing like a slinky with audible harmonic repeats on top of the fundamental vibration. It's hard to explain. And then sometimes a tank will just sound "thin". Sometimes both things are happening. But the real problem I've had, more so than bad tone, would be stability. I have yet to run across a new reverb tank that doesn't need extra isolation above the standard bag to be stable.

I did a test once when I had a Fender amp on the bench and I happened to have a purchased reverb tank of the correct type that I rejected for a build (but just couldn't bring myself to toss in the trash). I plugged in the tank I bought and sure enough there was instability and bad tone. So I've become of the opinion that good sounding, stable tanks are only possible with selection and the tanks we, the diy and repair community get from venders are the ones that didn't make the cut for Fender orders. Or something like that. Same with tubes to some degree as well. A company like Marshall or Fender has the power to say "This design works so the problem is these crappy tanks we're sending back." And the manufacturers HAVE TO respect that for a lot of reasons. So when a tank or tube order is filled for a major amp manufacturer it's not the same thing as when "Mike's Tubes and Tanks" (fictitious) places an order. And Mikes Tubes and Tanks just packs and sells whatever he's sent. That's what we get. There's almost no threat that responsibility for a sub par or under performing product will ever get back to the manufacturer in this scenario.

[Helmholtz]

Now if Fender still can get good sounding tanks, that means that there isn't a problem of non-availability of suitable raw materials.
Rather looks like a QC issue solely.

...and sure enough there was instability

Chuck H, what do you mean with instability? Acoustic feedback?

[g1]

Now if Fender still can get good sounding tanks, that means that there isn't a problem of non-availability of suitable raw materials.

We talked in another thread about the new Fender amps that have the Ruby brand tanks in them. They are 4AB tanks (edit: no they are not) but one of the transducers measures very different (DC) from the standard.
This makes me wonder if Fender can actually 'still get good sounding tanks' or why they used those Ruby tanks, and if they are still using them.

[Helmholtz]

This makes me wonder if Fender can actually 'still get good sounding tanks' or why they used those Ruby tanks, and if they are still using them.

They might use Ruby tanks because they sound good - and/or because it was the best offer.
How would this affect my point?

[g1]

How would this affect my point?

I think sometimes QC issues can be due to reduced availability of quality raw materials. If you have to accept less consistent materials, your end product may be less consistent. Or you won't be able to deliver enough quality product.
I don't know, but I think it must be some combination of the two factors.

For Fender to change the spec. of their 064063 tank from 4AB3C1B to RRVL2AB1C1BV4 (Belton) is very strange, especially going from long to short delay.
I did not find it a good sounding tank at all, I guess it's possible there was a short term loss of regular supply, and they may have changed back to the usual 4AB3C1B.
If they are still using these tanks, I would say they can't get good sounding ones on a consistent enough basis. It may be all QC as you say, but perhaps it's like modern tubes, a combination of QC and raw materials?

Your assessment was that the new type would have weaker output unless the magnets compensated, but that still leaves the delay length. Here is the thread: (skp to 2nd half of post #1)
https://music-electronics-forum.com/...reverb-changes

[Chuck H]

Now if Fender still can get good sounding tanks, that means that there isn't a problem of non-availability of suitable raw materials.
Rather looks like a QC issue solely.



Chuck H, what do you mean with instability? Acoustic feedback?

Yes. Sorry. I thought that would be clear since I followed by indicating "extra isolation above the standard bag" when I mentioned instability earlier in that thread. FWIW thin memory foam works pretty well.

EDIT: On a different note... The last reverb amp I built actually did have some unusual problems. One was that I couldn't find a quiet place for the tank at the bottom of the cabinet. No changing of orientation or scootching it around would mitigate hum induced by the PT. Yes, the tank itself was grounded and the PT in the amp was in a typical location at one end of the chassis. This was a 2x12 cabinet so there was plenty of room to play with, but no dice. I ended up having to mount the tank width wise vertical on the lower rear baffle as the only place I could get it to shun hum from the PT. It's more sensitive to reverb crash like this but only if it's being moved while it's on. i know they make tanks specifically for this orientation but try finding one. Plus I had an amp to deliver.

Another oddity that I had never run up against was a parasitic oscillation. The amp would whistle when the reverb was engaged and it wasn't acoustic feedback. The only thing that cured this was to ground the speaker frames. There was a lot of hair pulling, time and effort arriving at this discovery but currently the speaker frames are grounded because that's how it works.

[Leo_Gnardo]

Did he load the output of the reverb transformer or pull the AT7 tube? I've experienced some Fender amps that generate unpleasant artifacts if the reverb tranny is unloaded. Then there's the safety of the little transformer and the tube driving it.

No loading & took the usual reverb drive signal generated by 12AT7 and transformer. Yes I've occasionally run across Fenders (and other makes) that create unwanted noises/distortion with unloaded reverb transformer. On this Deluxe Reverb, no such problems. The owner is such a careful listener he even hears things he imagines, one of those Princess And The Pea types. If there was any unwanted response, I'd have heard about it. A lot.