Reverb Tanks Explained

Would you like to know what those numbers on a reverb tank mean?

Evatco carries a wide range of reverb tanks covering both MOD and Accutronics. We also carry digital reverb solutions with the Accutronics Bricks but let’s stick to the tanks for now.

There are essentially 3 types of tank but you will probably recognise these as large and small when you first look at them,

Large, which often start with the number 4 or 9 are approximately (assuming you are looking at these flat on a table)

• 425mm Long
• 108 mm wide
• 38mm high

Small, which often start with the number 8 are approximately (assuming you are looking at these flat on a table)

• 235mm Long
• 86 mm wide
• 38mm high

So why did I place the disclaimer (assuming you are looking at these flat on a table), well that’s because some tanks are designed to be installed on the base of an amplifier and others on the side or vertically, so which is top bottom etc vary.

Lets understand the first digit.

• Type 4
• Type 8
• Type 9

Type 4

Reverb tanks that start with a 4 have 4 counter wound and coupled springs and have been used in quite a few famous amps over the years

Type 8

Reverb tanks that start with an 8 have 3 springs in them and are designed for compact situations, don’t let the size fool you, these are my favourite reverb tanks. The size does not make that much difference and really does cover the key sounds you come to expect from a spring reverb.

Type 9

Reverb tanks that start with a 9 have 6 springs counter wound, coupled and arranged in parallel and are ultimately designed for use in amps that require a large luxurious sound e.g., pedal steel guitars.

What are the numbers on a reverb tank?

The numbers on a reverb tank haven’t really changed over the years, some models designed for specific companies may have unique numbers from time to time but these numbers should cover the majority.

The numbers found on most reverb tanks are 7 digits long and contain both letters and numbers

These numbers represent the following

• 1^st digit      Reverb Type
• 2^nd digit     Input impedance
• 3^rd digit      Output impedance
• 4^th digit      Decay
• 5^th digit      Connectors
• 6^th digit      Locking device
• 7^th digit      Mounting plane

1^st Digit – Reverb Type, reverb

Generally, this will be either a 1,4,8 or 9

2^nd Digit Is the impedance device, represented by a letter

• A       8 Ω   – 10 Ω
• B       105 Ω – 190 Ω
• C      200 Ω – 240 Ω
• D      250 Ω – 310 Ω
• E       600 Ω – 800 Ω
• F       1,475 Ω – 1,925 Ω

3^rd Digit Output Impedance, represented by letter

• A       500 Ω – 600 Ω
• B       2,250 Ω – 2,575 Ω
• C      10,000 Ω  – 12,000 Ω

4^TH Digit – Decay Time, represented by a number

• 1       Short        1.2 to 2 Seconds
• 2       Medium    1.75 to 3 Seconds
• 3       Long          2.75 to 4 Seconds

5th Digit – Connector type, represented by a letter

• A       Input Grounded / Output Grounded
• B       Input Grounded / Output Insulated
• C      Input Insulated / Output Grounded
• D      Input Insulated / Output Insulated
• E       No Outer Channel

6^th Digit – Locking Device, represented by a number

• 1 - No Lock

7^th Digit – Mounting Plane, Represented by a letter

• 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

So let’s look at an example

8AB2A1B

Well, that’s about all you need to know.

What if I cant find my number?

There are, from time to time, tanks that either don’t have a number or don’t quite match, consider your options through the key information provided e.g.

• Digit 1 is Optional – While ideally you should match, Its not mandatory
• Digit 2 is Important – You need to be in this range
• Digit 3 is Important – You need to be in this range
• Digit 4 is Optional – While ideally you should match, Its not mandatory
• Digit 5 is Important – Match required
• Digit 6 is Optional – Not required
• Digit 7 is Ideally matched but I have seen plenty of amps with this option ignored. I personally match where available .

Good luck