Magnatone MP-3 Reverb Tank?

[twilightofthedogs]

I am trying to sort out the reverb on an old Magntatone MP-3. I have the original tank, but its broken and resistances are unreadable. Is it possible to figure out which tank to get using the schematic? I know its above my head! See attached.

[TomCarlos]

Are there any markings on the tank? Can you take a photo of the inside? We can look at the number of springs and then take a guess.

[twilightofthedogs]

Thanks! No real markings except the date code (6633) and an "F" on the inside near the input

[TomCarlos]

If you look under the yellow tape, it could give you the manufacturer. It might be "Gibbs" ... a maybe for Accutronics. It does say subsidiary of Hammond.

I did a web search on Magnatone Reverb Tank. I found a reference to the Accutronics 4FB2A1B. On the Amp Repair Parts web site, it states that this tank was used in several Magnatone amps. So I am just taking an educated guess here.

[The Dude]

I don't think that tank will work. I'd expect a tube/transformer driven reverb to have a much lower input impedance. In fact the schematic shows that the reverb transformer (T1) has an 8 ohm secondary.

[twilightofthedogs]

Thanks guys. It's a gibbs tank. I actually can get a input resistance reading. It's about 1.8 ohms. Not sure how that translates to impedance. Its the output that the transducer is really messed up on. I tried it with the tank from a vintage super reverb, and that didnt work. I have a couple old ampeg reverberrockets and a maestro ga-1rt i can fish the tanks out of and try. Just wondering if there was a more scientific way to figure it out.

[TomCarlos]

It's not an easy conversion to go from a DC reading to Impedance. But, at least you know it is the output transducer. There could be a frayed wire? Time to get out the magnifying glass. The transducer wires are very small and soldering to the lead that goes to the RCA is difficcult, but not impossible.

Check out this video - the guy is repairing a Gibbs Type F reverb tank. And it is an 8 ohm input (as The Dude suggested). Look inside your tank again to see if you see a single letter.

Premier Twin 8R Reverb Repair

[TomCarlos]

Shoot.... I forgot to add...

Go to the Antique Electronic Supply site and review the page "Spring Reverb Tanks Explained and Compared."

[Helmholtz]

Thanks guys. It's a gibbs tank. I actually can get a input resistance reading. It's about 1.8 ohms. Not sure how that translates to impedance. Its the output that the transducer is really messed up on. I tried it with the tank from a vintage super reverb, and that didnt work. I have a couple old ampeg reverberrockets and a maestro ga-1rt i can fish the tanks out of and try. Just wondering if there was a more scientific way to figure it out.

That DCR of 1.8R clearly indicates an 8 Ohm input transducer as specified in the schematic.

A good Super Rev. tank should definitely work, might even be the correct type.
If not, there's another problem. Check cables, see if input and output are interchanged?

Those Gibbs/Hammond tanks are great sounding. Def. worth trying a repair.

[Tom Phillips]

...I tried it with the tank from a vintage super reverb, and that didn't work...

That tank should have worked if the circuitry in the Magnatone amp is working properly. Following are some troubleshooting tests you can easily do without a tank connected:

1) Test the reverb return circuit.
With the amp turned on, touch the tip of the cable plug that connects to the "Output" jack of the reverb tank. You should hear a buzz similar to what you hear when you touch the open end of a guitar cable that is connected to an amp. Make sure that the "Reverb Depth" control is turned up when you do this. If you don't hear the buzz then there is something wrong with the reverb return circuit or the cable connection or the cable itself. You can use your ohmmeter to test for cable continuity with the amp TURNED OFF and unplugged from line power.

2) If the return circuit is working then test the reverb drive signal. Do this by patching the drive cable to a speaker and playing a signal into the amp. Any working speaker will do. It doesn't even need to be in a cabinet. If you don't hear anything then there is a problem with the drive circuit or the drive cable. If that's the case then test the cable as above.

Let us know what you discover and we will proceed from there.

[52 Bill]

I know that I have explained this before, but I give it another go here.

Back in the day there were basically only two types of reverb tanks Type "F" and Type "C". This was explained to me as being F for transformer driven (low input impedance) and C for Capacitor driven (high input impedance). There were other differences, but the major one was the input transducer differences.

While the Fender tank you tried should work, the photo of the original tank shows input and output grounded connectors. The Fender tank has a input not grounded. Try it again, but connect the ground of the input jack to the circuit ground.

[twilightofthedogs]

Thanks all. Don't know what I did before, but the reverb does work with my 64 Super Reverb Tank. Interestingly, the vintage tank from the SR had a grounded input jack so it worked fine. I had tried a newer tank from a fender 75 with an isolated input jack, and that didn't work until I grounded as explained by Bill 52 below. Anyway seems to work ok, not as deep or splashy as a fender, but that just might be how it is. A bit noisy too, really evident when all the treble is rolled off with the reverb tone. Still have a few things to check on that though. I'll update if I discover anything else.

[Tom Phillips]

Thanks all. Don't know what I did before, but the reverb does work with my 64 Super Reverb Tank...

I'm glad you got it working. Perhaps it didn't work the first time because the tank was was plugged in backwards during that test.

[Helmholtz]

Confusing info since the first post, like "resistances are unreadable".
Probably just bad contacts.

Glad it works now.

[Tom Phillips]

Confusing info since the first post, like "resistances are unreadable"...

As I understand it, the "resistances are unreadable" was referring to the original tank and the reverb is now working with a different tank from the OPs Fender Super Reverb amp.