Reverb Tank Placement in Amp Head

[TerryD]

Thanks again everyone with all the help on this Fender PA 100.  I have one channel original, one Blackface Twin and the last two chained for some nice gain.

The cabinet was in rough shape.  I'm doing some reconstructing.  The reverb tank was on the front panel of the head.  You might say right behind the grill cloth.  I wanted to make the front with some gaps/holes/ air flow as you see in some modern amps because of the four 6l6s.
Question:  Is it OK to put this Reverb Tank on the bottom of the amp head or will that screw things up noise wise?  Will it be too close to something it shouldn't be close to?

Also...Any channel switching ideas for these three channels?

[eleventeen]

If you go look at the Accutronics site (or facsimile thereof) you'll see that rev cans are indeed designated vertical mount, horiz mount with open side up, open side down, etc; based upon that, one assumes there IS some sort of difference and I don't know specifically what it is other than opining that there is probably some difference in how the internal aluminum channel is suspended by the mounting springs. 


http://sound.westhost.com/articles/reverb.htm


Will it completely not work if you mount your existing tank "wrong"? I doubt it, maybe you have to set the reverb to 5 instead of 4 or 3 instead of 4. All you can do is to give it a try, I don't think you'll take out the neighborhood or anything.

[2deaf]

Any vertical or horizontal Accutronics 4xxxxxx tank will work in any position.  They have four springs that suspend the aluminum sled in a centered position within the housing.  These springs can be adjusted by placing them in different holes in the housing.  The sled has two holes in it that have pegs from the housing going through them that limit the damage to your reverb when your amp falls out of the back of your pickup.  The springs are adjusted so that these pegs are centered in the sled holes when the tank is in its intended position.  No matter what position you put the tank in, the pegs will not be off-center enough to touch the sled. 

Mod tanks have a plastic bushing in the sled holes that can touch the pegs in certain incorrect positions which couples vibrations from the housing to the sled which can lead to acoustic feedback.  Either brand can have their springs moved to center the sled in whatever position you want to use.

I have heard that those little magnets are connected such that they are centered when the tank is in its intended position.  Maybe.  I can't measure any difference between different tanks and I can't tell any difference in sound or output when the tank is rotated.   

[Willabe]

If you go look at the Accutronics site (or facsimile thereof) you'll see that rev cans are indeed designated vertical mount, horiz mount with open side up, open side down, etc; based upon that, one assumes there IS some sort of difference and I don't know specifically what it is other than opining that there is probably some difference in how the internal aluminum channel is suspended by the mounting springs.

I have heard that those little magnets are connected such that they are centered when the tank is in its intended position.

It's not so much the sled, as you said you can move the sled's springs.

It's the way the verb springs are attached to the coils. At least on the accutronics tanks, maybe the other brands have changed/fixed this?

They set them up so that the weight of the springs doesn't pull the ends into contact with the coil. If you take a tank and mount it differently than it was set up for it can/will restrict the free movement of the reverb springs. 

[2deaf]

Question:  Is it OK to put this Reverb Tank on the bottom of the amp head or will that screw things up noise wise?

Shouldn't be any problem with noise.

As far as having the tank in a different plane, tip the amp onto its face and give it a try.

[TerryD]

I thought the reverb springs had to be such and such a distance from the transformers or there was some problem.  I didn't know this horizontal/vertical stuff.  I'm going to look inside the can with this in mind.

[2deaf]

I found my notes on the older Accutronic tanks and at that time I had concluded that all driver transducers were the same.  However, I had noted that the output transducers were not all the same and that there was a color code which I did not bother to document.  I also noted that any given tank sounded the same in any position.

The little magnets will not come anywhere near close enough to the transfomer laminates to make contact no matter what position you put the tank in.  They are centered in the laminates when the tank is positioned correctly.  They become off-centered when the tank is not positioned correctly which would decrease the efficiency of the output transducer.  It is difficult to collect conclusive empirical data on the efficiency of a device that responds to transients, especially when the transients are generated by me with a guitar pick.

[Willabe]

That's what I'm talking about the weight of the springs will pull them out of 'center' if you mount the tank  differently then they make them to be placed.

If it didn't make a difference why would they list them for different planes? Doesn't make sense from a profet stand point to have to make more (different) tanks AND have to stock them into more piles on more shelves. They'd just say 'can be mounted in any position' and be done with it.

They also state that the best plane to mount the verb tank is like what Fender used in their stand alone reverb. So even though they can adjust them somewhat at the factory, they still are not all equal to each other.

How much difference in sound? Apparently enough for them to have to make them differently and to put out information in their designer spec sheets on best placement. 

I gotta think that after the 1st 100K or so they pretty much had them figured out. 

[Mike_J]

Accutronic says that placing the tank on the wall is preferable to either hanging them from the top or installing them on the bottom.  As far as distance from the PT is concerned the earlier advice to try different positions is valid. 


I have been dealing with this issue in the design of an AB763 one channel circuit in a head cabinet.  Fender grounded the RCA jacks at the jacks on the back of the chassis.  Apparently this can cause ground loops in some amps.  Solution is to isolate the reverb jacks from the chassis and ground jack and the 220K resistor to the ground side of the cathode cap for that portion of the reverb circuit.

As far as the oscillation is concerned it appears to be caused by an interaction between the power transformer and the transducers in the tank.  Apparently the first thing to do is try moving the reverb tank to see if there is a place that reduces the oscillation and any hum.  Secondly, a metal plate can be bolted to the open side of the reverb tank and then the tank can be wrapped twice, all six sides in aluminum foil.  Then put the tank in a tolex bag.  This supposedly solves the oscillation problem and reduces or eliminates hum.


Haven't tried it myself but it makes sense to me.


Thanks
Mike

[Willabe]

As far as distance from the PT is concerned the earlier advice to try different positions is valid.

The verb tanks output is very weak, weaker than the input signal from the guitars PUP's. 

That end of the tank you want to keep as far away as possible from the PT.