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Post new topic Fender Vibrosonic reverb tank
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Author Topic:  Fender Vibrosonic reverb tank
Jonathan Shacklock


From:
London, UK
Post  Posted 8 Feb 2020 11:06 am    
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I suspect the reverb tank on my Vibrosonic needs replacing but I’d like to get some advice. On 10 it’s reverby but a bit lacklustre and disappointing, slightly distorted if you pick hard, no long tail. On 3 it’s barely there. On other Fenders I’ve never turned the reverb up beyond 3 so it seems wrong to me....? Replacing the reverb tube makes no difference and I’ve cleaned the plugs and sockets. I’ve inspected the tank and it looks ok to my untrained eye. Somebody had taped some foam around the floating pan, presumably to dampen the effect? But removing this makes no real difference.

Can reverb tanks go bad this way over time - just getting weak and lifeless? Or is it time to take the amp to a tech?
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Pete Burak

 

From:
Portland, OR USA
Post  Posted 8 Feb 2020 11:28 am    
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I agree 3-5 is about all you should need.
One possible test is to try a different Reverb Tank from possibly a Twin Reverb or Dual Shownman, etc. (You can just sit them back to back and swap wires on the amp. You dont need to remove the tank to do a quick test.)
Brand new MOD replacement tanks get good reports and are pretty inexpensive.
Other basic things...
Is the footswitch related to the problem?
Are the RCA cables reversed, or damaged?
Are those tiny wires inside the tank ok?
Are you sure it's the right tube?
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Jonathan Shacklock


From:
London, UK
Post  Posted 8 Feb 2020 1:26 pm    
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Pete, thanks for these suggestions!

I wish I’d thought of the different tank idea before I sold my old Fender. I have a Peavey N112 though, would that tank be OK to hook up?

I suspected the foot switch as it’s not original but with it disconnected the reverb behaves the same.

The RCA cables are connected output to ‘output’. That did give me pause, but someone had labelled both output sockets ‘Red’ and both input sockets ‘black’. I’ll try swapping, from what I can find out it can’t hurt anything.

Tiny wires look ok.

Definitely the right tube but I haven’t tried swapping v4 yet. I gather this is partly used in the reverb circuit...?
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Paul Sutherland

 

From:
Placerville, California
Post  Posted 8 Feb 2020 2:10 pm    
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There are two tubes to be considered in the Twin Reverb/Vibrosonic amps. V3 is the reverb send and V4 is the reverb return. They both need to be working in good order.
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Bill A. Moore


From:
Silver City, New Mexico, USA
Post  Posted 8 Feb 2020 6:27 pm    
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The SS Peavey tank is not the correct impedance!
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Jonathan Shacklock


From:
London, UK
Post  Posted 9 Feb 2020 2:26 am    
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Thanks Bill, I won’t try that!

I replaced the v4 tube and it didn’t improve anything. Also swapped the RCA cables and the reverb didn’t work at all. Think I’ll start looking at replacement tanks. I really appreciate everyone’s help.
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Ken Fox


From:
Nashville GA USA
Post  Posted 9 Feb 2020 7:52 am    
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Did you swap out V3? It is the reverb drive tube. Both halves of the dual triode drive the reverb transformer then send signal to the tank’s input jack
The output goes to the reverb volume control then on to 1/2 of the V4 triode

The tank input is low input impedance, around 8 ohms at 1000 kHz . A Peavey tanks had an input of around 1250 ohms. Not compatible at all

Your tank is typically a 4AB2C1B model number, two spring tank
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Jonathan Shacklock


From:
London, UK
Post  Posted 9 Feb 2020 10:36 am    
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Hi Ken, thanks, yes I swapped out V3 for another 12AT7.

My tank has this similar model number, is there a significant difference in the ‘3’? Any recommendations for a replacement?

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Ken Fox


From:
Nashville GA USA
Post  Posted 9 Feb 2020 10:40 am    
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DIGIT #1 - REVERB TYPE
8 = short tank, three springs
4 = long tank, two springs
9 = long tank, three springs

DIGIT #2 - INPUT IMPEDANCE
A = 8 Ohm
B = 150 Ohm
C = 200 Ohm
D = 250 Ohm
E = 600 Ohm
F = 1475 Ohm

DIGIT #3 - OUTPUT IMPEDANCE
A = 500 Ohm
B = 2250 Ohm
C = 10000 Ohm

DIGIT #4 - DECAY TIME
1 = Short (1.2 to 2.0 sec)
2 = Medium (1.75 to 3.0 sec)
3 = Long (2.75 to 4.0 sec)

DIGIT #5 - CONNECTORS
A = Input Grounded / Output Grounded
B = Input Grounded / Output Insulated
C = Input Insulated / Output Grounded
D = Input Insulated / Output Insulated
E = No Outer Channel

DIGIT #6 - LOCKING DEVICES
1 = No Lock

DIGIT #7 - MOUNTING PLANE
A = Horizontal Open Side Up
B = Horizontal Open Side Down
C = Vertical Connectors Up
D = Vertical Connectors Down
E = On End Input Up
F = On End Output Up
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Jonathan Shacklock


From:
London, UK
Post  Posted 9 Feb 2020 10:51 am    
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Thanks Ken, I’m learning a lot! Things are not right if I’m supposed to be hearing a long decay.
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Mike Schwartzman

 

From:
Maryland, USA
Post  Posted 9 Feb 2020 5:51 pm    
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If it's any help Johnathan, I had the same reverb tank as in your photo. Accutronics 4AB3C1B was in my Fender Vibroclone, which is a Bandmaster Reverb with a few modifications in a 15" speaker combo cabinet. I just it changed to a MOD reverb tank with the same model number and it's much improved. The Accutronics had become seemingly oversensitive with noises that shouldn't have been there.
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Jonathan Shacklock


From:
London, UK
Post  Posted 10 Feb 2020 9:22 am    
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Thanks Mike, good to know, I’ll check out the MOD.
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Michael Brebes

 

From:
Northridge CA
Post  Posted 11 Feb 2020 7:27 am    
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Here's a good technical paper on reverb tanks. At the end is a comparison of the four available brands of reverb tanks. I have also found the MOD to be my choice among the available brands.
https://www.tubesandmore.com/tech-corner/spring-reverb-tanks-explained-and-compared
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Dave Grafe


From:
Upstate NY
Post  Posted 16 Mar 2020 8:39 am    
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The condition you describe sounds like a blown reverb transformer. If swapping another Fender-appropriate tank brings no joy then there is your issue. If you can't find another OEM transformer most any 8-ohm output transformer will worh. Don't try to replace it yiurself unless you understand how to residual drain high voltage from the power supply.
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ajm

 

From:
Los Angeles
Post  Posted 16 Mar 2020 10:05 am    
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Jonathan: It's been a month since the original post/question.
Did you fix the problem?
If so, what was it?
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Steven Paris

 

From:
Los Angeles
Post  Posted 19 Mar 2020 5:28 am    
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Michael Brebes wrote:
Here's a good technical paper on reverb tanks. At the end is a comparison of the four available brands of reverb tanks. I have also found the MOD to be my choice among the available brands.

Thanks for the link. One question I cannot seem to find the answer to is:
What is the nominal output level difference between a 600 Ω output impedance tank and a 2.575K Ω one?
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Michael Brebes

 

From:
Northridge CA
Post  Posted 19 Mar 2020 6:21 am    
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If I remember my transformer theory from college electronics, I believe it could be two times the level for the higher impedance output.
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Michael Brebes
Instrument/amp/ pickup repair
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Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso

Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100
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Erv Niehaus


From:
Litchfield, MN, USA
Post  Posted 19 Mar 2020 8:40 am    
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I'm having the same problem with my Vibrasonic amp.
I just bought an original Fender reverb tank off the internet. Very Happy
Erv
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Steven Paris

 

From:
Los Angeles
Post  Posted 20 Mar 2020 5:38 am    
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Michael Brebes wrote:
If I remember my transformer theory from college electronics, I believe it could be two times the level for the higher impedance output.

Thanks--that was what I was thinking also; I guess I just needed somebody else to say it!
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Josh Yenne


From:
Sonoma California
Post  Posted 22 Mar 2020 11:47 am    
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Not sure if you've figured it out yet...

I LOVE an old crusty reverb tank LOVE em.. but i've had some that are just way to tired and clangy for real gigging and have had to replace them.

I HIGHLY recommend the Revisit tanks.... IMO they BLOW away both the Mods and the Accutronics being made these days.

They are slightly more expensive but thats by like 5 or 10 bucks.. tanks are CHEAP!
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Jonathan Shacklock


From:
London, UK
Post  Posted 12 May 2020 5:58 am    
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Apologies for not updating this thread earlier. I only just got round to replacing the tank. I did a little research on the Revisit brand and it seems that they are restickered TAD tanks which happen to be a few pounds cheaper than the MOD or Accutronics here in the UK. I’m sort of amazed how cheap reverb units are anyway.

I fitted the tank today and it fixed the problem, I’m totally happy with how it sounds, just as it should, and the reverb goes from subtle all the way to cavernous Cool. Thanks for the recommendation Josh, and everybody for their input.
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Steven Paris

 

From:
Los Angeles
Post  Posted 12 May 2020 9:10 pm    
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Jonathan Shacklock wrote:
..... the Revisit brand and it seems that they are re-stickered TAD tanks which happen to be a few pounds cheaper than the MOD or Accutronics here in the UK.

That's interesting....what is the source of this information? So the tank you installed was a TAD?
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Jonathan Shacklock


From:
London, UK
Post  Posted 13 May 2020 2:28 am    
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Good question Steven, the waters are definitely muddy here but take a look at the TAD data sheet (dated 05/11/2010) and compare it to the Revisit webpage (first captured on the wayback machine in 2012) 


https://www.tubeampdoctor.com/media/pdf/ba/fa/78/tad-reverb-datasheet.pdf

http://amprepairparts.com/reverb.htm

The Revisit photo looks to have had the TAD code photoshopped out although they left the TAD sticker on (top left). This doesn’t necessarily mean much on its own: it’s possible the photo is “only for illustration purposes” and the actual Revisit units have slightly different tooling or components.

 That said, the fourth post down here seems to confirm my suspicions:



“Revisit reverb tanks are exactly the same as Mojo and TAD reverb tanks. They're made in the same facility*. The only difference is the paint color and 3 year warranty. Revisit confirmed this when I questioned them about it. They're good reverb tanks as far as new reverb tanks go, but there's nothing proprietary or custom about them.”


https://www.thegearpage.net/board/index.php?threads/favorite-reverb-tank.1244677

It should be said that there are somewhat contradictory posts in that thread and elsewhere on the internet (plenty of sticker debate here thehttps://surfguitar101.com/forums/topic/30892/?page=1) so who really knows?

Revisit are apparently quite open about it if you ask them and they may well have their own quality control procedures or better packaging... something that warrants different branding in the same way that tubes or strings are often remarketed (if that’s a word). Certainly the warranty is worth something, although I see it’s gone down to 2 years.



Anyway, I installed the TAD branded tank, which itself has some small differences from their pictures (finish is the same but both input connectors are white, not red and white, and the rectangular cutouts in the pan look to have wider spacing compared to the same model). I’m no expert but I’m very happy with it so far. It’s probably going to be a long time before I can gig with it unfortunately but it’s a huge improvement on the weak and weary original Accutronics.



I’m just trying to decide wether to keep the original cardboard base - (un)surprisingly there are various tone mojo claims made for the cardboard vs no base so that’s a whole other rabbit hole…!


*Probably in China https://surfguitar101.com/forums/topic/30892/?page=2
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