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SurfGuitar101 Forums » Gear »

Permalink Gibbs reverb tanks codes compilation

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The codes on the old 60's Gibbs pans look like a 'mess' and so far I haven't found any 'official' info that explains what all the codes stand for.
So, I've gone through hundreds of threads on various guitar forums and many online ads on dozens of 'second-hand items sites'/ CL's in various countries.
The aim was twofold:
1) just see what is out there as far as codes go
2) find info on the input and output impedance for each Gibbs code.

The final goal is obviously to find out what Gibbs pans can be used in a standard outboard reverb unit like a 6G15, Surfy Bear etc.
I've put my conclusion at the bottom as to which pans you can 'safely' buy for a 6G15 or Surfy Bear..

Some explanation on the abbreviations:
I = input impedance (DC measued)
O = output impedance (DC measured)
y = year

Sometimes I could only see the inside of the pan, sometimes only the outside, other times both.

Marked with a letter on the inside and Input/Output measured by the owner or seller:
These could be marked on the outside with additional codes as well or not.(I couldn't see, owner/seller didn't tell, or code on the outside was missing)
Between brackets is what various owners/sellers measured for in/out.

L (I:183 O:173) (I:170 O:170) (I:165 O:165) (I:178 O:188) (I:168 O:171)
C (I:135 O:135) (I:181 O:183) (I:200 O:200)
U (I:12 O:12 *suspicious, does not correspond to any known in/out,contradicts Accutronics info below)
R (I:? O:175) (I:1 O:169)
K (I:1,3 O:41) (I:1 O:44) (I:1,3 O:40)
4U (I:1,7 O:200)
4V (I:180 O:180) (I:166.2 O:166.7)

Marked with a code on the outside and Input/Output measured by the owner or seller:
These could be marked on the inside with additional codes as well or not. (I couldn't see, owner/seller didn't tell or code on the inside was missing)

AO-23580-10 (I:1 O:40) (I:1,3 O:41) (I:1,4 O:41,8)
AO-23580-11 (I:176 O:180.6) (I:165 O:165) (I:175 O:176) (I:168 O:171)
A0-23580-15 (I:1.3 O:174.2) (I:1,4 0:167)

Marked on the outside and inside but not measured:
I only listed distinct combinations, by which I mean: all the 15's had R inside and all the 11's had L inside. There were no 15's with any other code than R, idem dito for the others.

AO-23580-10 K
AO-23580-11 L
A0-23580-15 R
AO-23580-17 4U
AO-23580-18 4V

Info given by an Accutronics representative in response to an e-mail from a forum member:
The letters without corresponding Accutronics code are some that I found on photos (in ads, google images etc)

C = 4FB2A1C
D = 4AB1A1E
F = 4AB2A1C
G =
K = 4AA1C1C
M =
L = 4FB2B2C or 4FB1B1C
P =
R = 4AB????
U = 4AB1C1C
V = 4FB1C1E

Change of coding system
At some point in time, the codes changed from using "AO-23580-X" to "121-0000X".
Once I realised this happened, I went back to check the dates on those specific pans to see at what time they changed the coding system, which is why you see a year added here and not with the other pans above, which iirc were all 60's pans.

121-000048 (P inside) (I:1,2 O:176) (y:1970)
121-000049 (R inside) (I:1,1 O:171) (y:1969)
121-000022 (4U inside) (y:1969)
121-000051 (U inside) (I:1.1 O:172) (y:????) Additionally marked 1122-7044 on the outside
121-000051 (4U inside) (I:1.1,6 O:168) (y:1969) Additionally marked 1122-6911 on the outside
121-000052 (nothing inside) (I:176 O:176) (y:1971)
1121-00052 (C inside) (I:178 O:177 ) (y:????)

No system found:
Then there were pans with codes that didn't fit in any of the above coding systems:

VV3363 (I:1.3 O:173.4)
"Gibbs 984-003365 spring reverb unit 1968" (I:169 O:171)

VV2963 1122 6320 (F inside) (I:1.2 O: 171.6)

64063 (4U1 inside)
64063 (I:1.1 O: 172)

VC3130

(820209 inside) (I:183 O:187)

Decay time or length
One thing I noticed early on is that there was no code for decay, like the 3=long, 2=medium, 1=short in Accutronics pans.
So, while going through all those forum threads, I was also on the lookout for info about the decay time. Very little could be found but here's some:
Quoting various 'people':

As far as I remember, the early tanks were all made the same way with no specific mounting or other physical restrictions.

Some research led me to find out that the "R" stamp signifies "medium decay" with the correct Fender impedances.

The 63 Fender Standalone reverb comes with a Gibbs model F.
Typically Gibbs put this mark inside the reverb by the input connector, stamped in ink.
The Gibbs F unit is the same as an Accutronics model 4AB2A1C.
If you have the 63 Fender Standalone reissue then the reverb would be a 4AB3C1C

It seems the Gibbs and Accutronics pans from the 60s and EARLY 70s (like 70/71..) have shorter decay and a brighter, drippier drip.
The later ones seem to be a bit darker and longer decay. This is from a small sample of 5 or 6 tanks

Gibbs took over production from Hammond in 1964


Conclusion:

Whenever you see an old Gibbs pan on Ebay, CL, or whatever local second-hand items website you're on, there's always the question if it will work in your circuit.

Most sellers don't know how to measure the input/output impedance, don't want to or simply don't have a multimeter.

What's important for us (using 6G15, Surfy Bear or similar) is the input and output impedance.

By compiling the list above you know what type pan you'll get purely based on the Gibbs codes and markings.

We need a pan with a (DC) input resistance ranging between 0.8 and 2 Ohm and a (DC) output resistance ranging between 165 and 270 Ohm. Accutronics lists them as 0.8 Ohm and 200 Ohm.

If a Gibbs pan is marked with any of the codes below it will be a substitute for an Accutronics '4AB' pan:

Marked on the inside:
- P, R or 4U (decay unknown, probably medium)
- D or U (short decay)
- F (medium decay)

Marked on the outside (decay all unkown):
- A0-23580-15 (if marked inside it's always R)
- AO-23580-17 (if marked inside it's always 4U)
- 121-000022 (if marked inside it's always 4U)
- 121-000048 (if marked inside it's always P)
- 121-000049 (if marked inside it's always R)
- 121-000051 (marked U inside, short decay)
- 121-000051 (marked 4U inside, medium decay)
- VV3363
- VV2963 6320 (marked F inside)
- 64063 (if marked inside it's always 4U1)

The above will work as far as input / output impedance goes (which would be hard to modify yourself) but may not have the correct grounded/isolated code or mounting orientation code (both of which are very easy to modify to your needs)

So far it seems there are no 'long decay' Gibbs pans... those are the only ones I'm interested in. Argh

As a counter balance for all the times I mentioned Gibbs:
image

Last edited: Mar 28, 2022 03:01:56

Awesome sleuthing! I just noticed last night there is a Gibbs pan in the ‘64 tank. Gonna have to check the code, exciting! It doesn’t drip as much as I’d like, so maybe it’s not the original. Or maybe it just needs a chopstick.

Daniel Deathtide

I've personally found many sellers were able to check impedence once coached on how to do so.

Danny Snyder

Latest project - Now That's What I Call SURF

"With great reverb comes great responsibility" - Uncle Leo

My savior!!!! Thank you SOOOOOOO much. Headbang

sidenote:

NCIS reference dropped me. Cheers

Last edited: May 13, 2020 10:50:13

SurfDub wrote:

My savior!!!! Thank you SOOOOOOO much. Headbang

You're welcome.
I had fun collecting all that data.
I'm glad it also helped.

Last edited: May 15, 2020 11:18:00

I'm coming out of lurking to just to say THANK YOU to @j_flanders for providing this invaluable reference.

I have a '63 Reverb reissue with the 6K6 tube swap that came with a USA Accutronics pan. Lately I had been dissatisfied with the tone, which was pretty drippy but otherwise kind of harsh and pingy. I tried epoxying the spring junctions and jammed toothpicks into the loose transformers, but that didn't help much.

I also tried a new Korean Accutronics pan, which sounded smoother and more lush, but had rather poor drip.

I decided to hunt down a vintage Gibbs pan and my search for information brought me to this thread. I'm happy to report that I found the 'right' Gibbs pan on eBay, a 1969 121-000051 with a 4U stamp inside, and it sounds fantastic.

Last edited: Mar 24, 2022 19:53:57

beatcomber, I've found that many sellers of reverb pans are willing to check the resistance of the input and output jack for you, so you'll know in advance if it'll work.

Danny Snyder

Latest project - Now That's What I Call SURF

"With great reverb comes great responsibility" - Uncle Leo

Here's a look at the pan I just got:

image
image
image

As received, it still had a bunch of mounting brackets from the Hammond organ, all of which I had to remove (and discard). No big deal!

(That yucky brown carpet is most definitely not in my home, the last image is from the seller's eBay listing.)

image

Last edited: Mar 25, 2022 06:58:06

DannySnyder wrote:

beatcomber, I've found that many sellers of reverb pans are willing to check the resistance of the input and output jack for you, so you'll know in advance if it'll work.

Good tip!

beatcomber wrote:

I'm coming out of lurking to just to say THANK YOU to @j_flanders for providing this invaluable reference.

I'm happy to report that I found the 'right' Gibbs pan on eBay, a 1969 121-000051 with a 4U stamp inside, and it sounds fantastic.

That's great to hear! Have fun with the pan.
I have added yours to the list.
My guess is then that the 6911 stands for week 11 in the year 1969.

Last edited: Mar 25, 2022 07:23:52

_j_flanders wrote:

That's great to hear! Have fun with the pan.
I have added yours to the list.
My guess is then that the 6911 stands for week 11 in the year 1969.

Thank you! I agree with your interpretation of the date code. That means it was made sometime between Mar. 10 and Mar. 16, 1969 - almost exactly 53 years ago this week.

I just measured the impedance on my 121-000051 4U... I: 1.6, O: 168.

Last edited: Mar 27, 2022 19:51:04

Yup, that's what you want. <2Ω and around 170Ω

Danny Snyder

Latest project - Now That's What I Call SURF

"With great reverb comes great responsibility" - Uncle Leo

beatcomber wrote:

I just measured the impedance on my 121-000051 4U... I: 1.6, O: 168.

Thanks for measuring. I'll add it to the list.

DannySnyder wrote:

Yup, that's what you want. <2Ω and around 170Ω

It's nice when something works out according to plan!

This past weekend, I visited forumite LordWellfleet and brought along my Fender '63 Reverb reissue, upgraded with a 6K6 and Gibbs 121-000051 4U pan. Ed (LordWellfleet) has a nice Texotica Reverb, also with a 6K6, and USA Accutronics pan; I wanted to do a shootout and see how the two compared.

We went back and forth between the two units and the clear winner was the Fender with the Gibbs pan. Ed's exact comment was "This is exactly what a Fender Reverb is supposed to sound like."

In no way is this a disparagement of the Texotica, but a demonstration of the relative difference between the vintage Gibbs and the Accutronics. Had we gotten around to swapping the pans between the two units, it would not have surprised me if the handwired, boo-teek Texotica pulled ahead with the Gibbs pan installed.

What we heard from the Gibbs was way more of a 3D lushness and a nuanced drip that sounded like droplets of water spraying up into the air. Switching to the Texotica with the Accutronics after experiencing the Gibbs was quite literally a bummer.

Ed is now on the hunt for a Gibbs pan!

First post here. I thought I'd add my info, as this thread helped me when I was trying to source a replacement tank. I recently had a 1964 Supro Big Star S6451TR on my bench with reverb issues. These came from the factory with a cardboard-boxed Gibbs short-tank 2 spring reverb. The word on the web is that these tanks don't sound all that great. I was lucky enough that both transducers "seem" to work. I got a DCR of 1.1 ohms on the input and 261.5 on the output and used that info to source a modern replacement, despite so many knowledgeable techs saying "It says 4F right on the schematic!" IDK what the original tanks sounded like, but the owner was happy with the sound of the new tank. I'm trying to repair the original, but I'll start my own thread for that. I'll attach a few pics here for posterity.
image
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