Microphonic 4AB3C1B reverb tank

[punkykatt]

What would make a reverb tank howl and squeal? Swapped in another tank same value and all is fine. Anyone here try to fix one? R reading on input and output look normal. The tank actually vibrates when it howls.

[tubeswell]

Acoustic feedback on the pan case. Try another pan, or put a strip of corrugated (packaging) cardboard or plastic bubble wrap around the pan before sticking the pan back inside the bag.

[Williamblake]

Doesnt this happen if you drive the tank real hard? Tank rattles and the signal out of the tank sounds like a ship's horn.

[punkykatt]

Yes, turn up the reverb pot and she starts to howl all on its own without playing a note. The tank is sensitive to the slightest touch. Loose input coil? I will try wrapping in bubble wrap. Thx tubeswell.

[PRR]

So when it is howling, is there some inside part you touch and it damps (or encourages) the howl?

(May want your shooter earmuffs for this experiment.)

[Latole]

Try to stop transducers moving in the tank with toothpicks.
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Why are reverb tanks in bags?
Reverb tank bags give the reverb tank better isolation which results is fuller, richer reverb.
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https://www.amplifiedparts.com/tech-articles/spring-reverb-tanks-explained-and-compared

Spring Reverb Construction and Operation

The main components used to produce the spring reverb effect are:

Input and Output Transducers - Each transducer consists of a coil centered around a magnetic lamination and small cylindrical magnets centered in the air gap of the lamination.
Transmission Springs
These components are mounted on an inner aluminum channel, which is connected by four small support springs to an outer steel chassis (or channel).

An electrical signal applied to the input transducer coil generates an alternating magnetic field which moves the transducer magnets. The magnets are mechanically coupled to transmission springs. The signal is reflected back and forth through the transmission springs with an amount of delay determined by each spring's diameter, wire gauge, and length. The moving magnets of the output transducer generate an alternating magnetic field which induces an electrical signal in the output transducer coil.

[punkykatt]

HAPPY EASTER everyone!!!   Great info, much, appreciated. Thanks Guys.

[Latole]

Happy Easter to you to and goo luck with your reverb tank !

[punkykatt]

Well the toothpick trick stopped the howl. Took a piece of sandpaper and sharpened one end of the tooth pick to a fine chisel edge and wedged it between the input coil and the laminations. Put a dab of Shoe Goo adhesive on it to hold it in place. Still had the squeal, so I used a 1/2" thick sheet of foam rubber, cut into two pieces the size if the tank, one under the cardboard on the bottom of the tank in the bag and the other on top of the tank in the bag. Worked pretty well. I ordered a new tank for the customer to play it safe (I will be away from mid May to early October this year in case that tank poops the bed) Im going to keep this tank for a backup test tank.  Thank you all again for your reply's.

[Latole]

Good job

Back up reverb tank is very useful. I have few.