magnetically shielding reverb tank?

[Smedley Smorganoff]

So, I put two Weber speakers into my 63 Vibroverb RI. The magnets are huge, and the tone is amazing.

However, the magnets are so huge that I suspect they have been causing my reverb tank to feedback. I've ruled out tubes and cables/wiring. The amp would feedback with the reverb turned up past 5 - even with no guitar plugged in. I placed the reverb tank outside the amp, and voila, no feedback!

Would magnetically shielding the reverb tank solve the problem? How would I go about doing that?

Any help is appeciated.

 

[Cygnus X1]

Try flipping the reverb tank on the long axis 180 degrees.

 

[Soul Tramp]

This is a known problem with reverb tanks. Try wrapping it in tin foil that's grounded to the RCA jack shields.

 

[Cygnus X1]

On Don's suggestion just check and see if the tank is actually grounded to its own chassis.
Or not...

Here is a great resource, probably more than you need to know.

http://electricalfun.com/WorkbenchFun/reverb_tank.pdf

 

[Six Gun]

Buy a piece of Lead roofing flashing, wrap it over the top of the tank on both sides so it's all shielded, problem solved. It comes in like 12" widths, get 2' feet of it.

I did it to a Princeton Reverb, the tank was so close to the magnet, works great.

Home Depot , Lowes etc.

 

[Smedley Smorganoff]

Thanks for the suggestions, guys. I'll try rotating it first, and it that doesn't work, I'll try one of the other ones. I'll report back, no time this week.

 

[Cygnus X1]

Try flipping the reverb tank on the long axis 180 degrees.

Brilliant!

 

[Soul Tramp]

Try flipping the reverb tank on the long axis 180 degrees.

I don't understand how that would help. Please explain.

Reversing the direction of the tank may help if it distances the tank transformers outside the speaker EMF shadow.

 

[Cygnus X1]

I don't understand how that would help. Please explain.

Reversing the direction of the tank may help if it distances the tank transformers outside the speaker EMF shadow.

Sometimes it works, changes the orientation of the transducers to potential interference (hum).

What was "brilliant" was the fact that the new member here stated it exactly as I did, without quote or comment.
I was being sarcastic.

I think someone is just trying to run up their post count.

Odd, I think the user has vanished into thin air!

 

[Six Gun]

I told you about the lead roofing flashing, works the best so far.

Wrapping the tank in a wet suit neoprene material works good too,
but the lead by far shields the magnetic field 100% from the magnet.

It's the magnetic strength of the speaker, it;s so strong it is pulling on the
reverb tank springs. The springs are so sensitive they are designed to be
free of any magnetic field. Weber speakers are so strong having a reverb tank right under the speakers will not help anything unless you either shield it, or remove it and mount it in a small box and keep it outside the back of the cab.

For you guys who know Fender Vintage gear, the early Deluxe Reverb and Princeton Reverb amps use a thick cloth tolex type material and they sewed a double-thick bag system to help on the shielding. After 1966 into 1967 Fender switched to a cheaper thinner reverb tank bag. And after that an even thinner, cheaper thin bag.

Even sliding a 1/2" thick piece of cardboard in the reverb tank bag to cover the top of the reverb tank while in the bag will help you a lot. Custom thick leather reverb tank bags work well too.

I have tried over a dozen systems, the 12" roofing lead sheet metal that is sold in a roll at Lowes, Home Depot, sold by the foot, is the absolute best for 100% shielding from the magnetic field that affects the tank-springs.

It's not about the signal, it;s about the magnetic field affecting the springs from vibrating free as they should..

A sheet of ABS plastic cut to size, and slide into the tank cover may help shield the system.

 

[Six Gun]

Look at this pic of my wireless on the top of the rack, it also has lead shielding around the road-case to help shield any other interference.
This is a second application where the 12" lead roofing flashing works well.
They sell 2#, 2.5# and thicker, the 2# Lead is 1/32" thick and this is all you need. Home Depot, Lowes sells the 2# lead.

Those amps in the racks are the newest Crown IT12000HD amps, solid.

 

[Cygnus X1]

Sounds great to me six gun.

We obviously got sidetracked!

 

[Soul Tramp]

Sometimes it works, changes the orientation of the transducers to potential interference (hum).

What was "brilliant" was the fact that the new member here stated it exactly as I did, without quote or comment.
I was being sarcastic.

I think someone is just trying to run up their post count.

Odd, I think the user has vanished into thin air!

My mistake. I misunderstood what Reneed was saying. I thought he meant the tank should be flipped upside down. That made no sense to me.

 

[Cygnus X1]

My mistake. I misunderstood what Reneed was saying. I thought he meant the tank should be flipped upside down. That made no sense to me.

In reality, if one looks back...you misunderstood what reneed was saying that I was saying.


I'll just defer to Six Gun on the whole deal.

 

[Smedley Smorganoff]

Well, I tried rotating the tank 180 degrees today and the feedback still happened. Gonna have to try the other methods now.

However, loosening the screws that hold the tank to the cabinet helped a bit. Moving the amp away from the wall also helped.

 

[Soul Tramp]

Since moving away from the wall helped, it means your problem is likely vibration, not EMF. Try putting very soft rubbery bushings between the tank and the cab to suspend it.

 

[Smedley Smorganoff]

Since moving away from the wall helped, it means your problem is likely vibration, not EMF. Try putting very soft rubbery bushings between the tank and the cab to suspend it.

Maybe you're right. But, it did feedback with the Reverb cranked to 10 with no guitar plugged in. Could it be both?

Thanks for suggesting suspending the tank; another option to try out. I'm a little unsure about raising the height of the tank though (puts it closer to the speaker magnets).

 

[Smedley Smorganoff]

Buy a piece of Lead roofing flashing, wrap it over the top of the tank on both sides so it's all shielded, problem solved. It comes in like 12" widths, get 2' feet of it.

I did it to a Princeton Reverb, the tank was so close to the magnet, works great.

Home Depot , Lowes etc.

I know it's been 6 years, but I'm gonna go ahead and do this. What thickness of lead sheet did you use to remedy your Princeton Reverb?