Reverb tank question

[chillidoggy]

Is is possible to fit a smaller length reverb tank to my amp? What's the criteria? Does it have to match electronically or something? I've got a 9AB2C1B Accutronics, and need something with less length.

[thermionic]

I think you have to match the input/output impedances. You should be able to find the relevant data for yours from the model number, then see if Accutronics (or somebody else) make a shorter one. If the tank is driven by an opamp circuit rather than a valve and its associated output transformer you may be able to get away with a less than perfect match (maybe? Don't quote me on that!)

[jpfamps]

Didn't think you'll find a shorter tank/

Why did you want one?

[ICBM]

A 9" Accutronics is about the shortest there is (apart from really crap ones), but if that's a full 17" one then you can change it - just match the impedances as thermionic said.

The usual consensus is that the short tanks don't sound quite as good though. Most people want to swap the other way round!

[jpfamps]

Sorry I wasn't paying attention!

Your tank is the longer 17" tank. You can get a 9" tank.

What the tank codes stand for is on the Accutronics site:

http://www.accutronicsreverb.com/

The first number in the tank code is the size of the tank, so you will want one starting with an 8.

The letters in the code are the most important for proper function. The AB at the start of the code indicate the input and output impedance of the tank (important for correct drive to the tank, and signal from the tank), and the C indicates how the tank is grounded (important for avoiding ground loops), and the B at the end indicates optimum orientation, although in my experience this doesn't make that much difference.

Anyhow, a 8AB3C1B would work fine, and is available from Tube Amp Doctor.

[chillidoggy]

I'm curious as to why you suggested the change to -

8AB "3" C1B?

Also I might need an A suffix due to the reverb tank might be required 'upside down'. Does it really make no difference? Seems strange that the manufacturer would produce them for different orientations if they weren't required.

[jpfamps]

I'm curious as to why you suggested the change to -

8AB "3" C1B?

Also I might need an A suffix due to the reverb tank might be required 'upside down'. Does it really make no difference? Seems strange that the manufacturer would produce them for different orientations if they weren't required.

I suggested this tank because it's available for sale off-the-shelf; not all combinations are.

You may struggle to find the exact tank you want. The tank I suggested is correct for the most important parameters. Using the wrong impedance and grounding configuration can lead to more problems than the wrong orientation and decay time.

A shorter tank will have a different sound anyway, so trying to match the decay time won't produce the same sound anyway.

Regarding the orientation, the tanks are designed so that the transducer magnets on the springs are centred in the transformer lamination gap. Thus the best way to mount the tank is vertically, gravity pulls the magnets along the gap rather than towards one side.

Having said this, I've compared the sound of B tanks upside down and correctly orientated, and can't hear much difference, if at all.

Anyhow, you can try this with the tank in your amp.

The main issue I've had with reverb tank orientation is optimizing it for low hum.

[ICBM]

+1. Make sure you orient it with the return end as far away from the amp's mains transformer as you can, and if it hums try moving it around a bit, if there's room.

I've often used "wrong" spare reverb tanks and rarely had a problem as long as the impedances match. You can easily fix grounding issues by cutting the ground in the cable or adding a separate one, if you have to.

[chillidoggy]

Much obliged chaps.

[chillidoggy]

Reverb tank bags. I've never had an amp with one fitted from new, and I've had one or two new amps.

Snake oil, or a useful addition?