Recycling old Gibbs/Accutroincs tanks

[Phil_S]

I'm putting this one in Garage Talk 'cause I'm not sure. eBait has old tanks pulled from who knows what (organs, I guess) going for rock bottom prices these days. I see an auction right now for a lot of 2 tanks that are going for $10 plus about the same for shipping. That's $10 each in the end. I figure, even if you get a dud, you don't really get hurt at that price.

From time to time, I see discussion on new Mod or Belton/Accutronics. Universally, the conclusion seems to be these aren't as good. That's what got me browsing. It raises a pile of questions.

How do I figure out what model it is? You know, tank orientation, input/output impdeance, delay, etc. The question goes directly to amp interface, mounting, and the proper driver transformer (or other means of driver.)

What kinds of things typically go bad on tanks? What's a fatal problem vs. a repairable problem? We can skip the obvious ones like broken springs and bent tanks ;-}

The low prices are tempting me. The other guy in my head says it'll be headed straight to the bin for recycled metals and on to the dump.

[R.G.]

Actually, I recently did a PCB that puts the Belton BTDR-2 into an old tank shell, reusing the form factor and mounting and requiring only an additional power connection to it so that you can replace a dead tank with an electronic tank.

That's what *I'd* do with a cheap, dead tank.

But what goes bad on the tanks is usually an open or shorted coil in the transducers.

You can tell what impedances and such were on a *good* tank by measuring the DC resistance of the coils and matching that to the legacy info about accutronics tanks. Some of them have color coding on the bobbins of the coils for which is which.

[Charlie Wilson]

Hello, I don't really like the sound of the newer tanks much either (I play surf music). If the transducer opens up, you can replace it with a good one from another broken tank if there is a good one you need on there. I have found the most common issue is the little wire that anchor the springs to the transducer break. I found that those little wires are soldered to a sleeve that sometimes can be removed and replaced with a good one. I keep a collection of broken pans that I MacGyver for parts.
CW

[Phil_S]

Wow! A whole different idea. I'd be starting from scratch, so there's no need for an old tank.

I see you can buy one of these Belton bricks for under $20. Now, if I could only figure out how to hook it up! It looks like I need a pot and a couple of Op Amps. The Op Amp is new territory for me. Are you willing to suggest a part number?

Thanks!

[Leo_Gnardo]

what goes bad on the tanks is usually an open or shorted coil in the transducers.

You can tell what impedances and such were on a *good* tank by measuring the DC resistance of the coils and matching that to the legacy info about accutronics tanks. Some of them have color coding on the bobbins of the coils for which is which.

I find occasionally broken lead-in wires, those can be mended. But for the last 10 years or so of USA Accutronics, there was a rash of coils going open. Seems to be coincident with the time they went to plug-in tabs on the transducers.

If you have the patience & dexterity you could swap out bad transducers for good. You'll have to unass the springs/clips & reattach them too. Too fiddly for me. But in case I ever have a mind to do it, got a box full of bad tanks, at least 20.

I find the tank boxes are good to build prototype projects into. I used one to build my 12A-7 tube gain tester. Just a pair of Fender style first stage preamps, no genius stuff here.

[frankleslie]

I have installed a Belton reverb brick in a newbuild and it Works very well. It taps off the signal from the volume pots wiper and inserts it back into the second grid of the phase inverter. The Associated Components is a high impedance buffer (dual op-amp) and an amp that gives 5 to 10 times gain, mine is about 7. The op-amp is a TL072 but any low noise Device will work. The Belton distorts (nastily) if the signal input is above 1,5V RMS so a bit of tweaking has to be done. I enclose a diagram of the one I found to work well in my build.

[TUBEDUDE]

If you are using op amps to drive the tank, some improvement can be made by using current drive instead of voltage drive. This eliminates the issue of rising impedance with frequency that the drive coil posesses.

[Phil_S]

Hey, thanks to everyone for all the info and especially for a circuit schematic! I have shifted my thinking here. If I'm going to build with reverb, it seems like I should use the brick, not a tank. I'm not a purist. Also, at my age, I can't hear what I used to.

On a moderately related note, I just came from seeing the ENT and audiologist last week. I have developed tinnitus. Apparently this is more common in men than women. The audiologist says my hearing is just fine. I learned they only test for speech frequency, which is 500Hz to 8KHz. I know I can hear A0 = 27.5Hz, and I'm pretty sure I'm topping out at around 11K. (I don't know if my PC speakers dropped out at 11K or if that is my ears' limit.)

[R.G.]

The Belton distorts (nastily) if the signal input is above 1,5V RMS so a bit of tweaking has to be done.

On my test circuits, I put a diode clipper in there so the diodes limited the signal to about +/- 1.4V peak. That clips earlier than the Belton, but the clipping is what our ears have come to expect, so it sounds a lot better than the absolute clipping of running off the end of the A-D converter at the input to the Belton.

Still clips, but sounds very, very much better when it does. I've heard that some people even purposely use clipping like this cause they like how it sounds.

[Phil_S]

I seem to be quickly running out of headroom on the how to do it parts of this. I was thinking about that build I've been posting about and putting reverb in it. The PT has a winding that is 3.15-1.25-0-1.25-3.15. I was wondering if it would be OK to share the 6.3V filament winding with the Belton? Can I take the 2.5V (probably 2.8V in real life), run it through a FW rectifier and split off the 1.4V I need with a voltage divider?

I'm figuring I'd ground the CT as that's necessary for the FW rectifier. What's this do to the filament circuit?

[Structo]

On a moderately related note, I just came from seeing the ENT and audiologist last week. I have developed tinnitus. Apparently this is more common in men than women. The audiologist says my hearing is just fine. I learned they only test for speech frequency, which is 500Hz to 8KHz. I know I can hear A0 = 27.5Hz, and I'm pretty sure I'm topping out at around 11K. (I don't know if my PC speakers dropped out at 11K or if that is my ears' limit.)

I've had it for years from construction noise and loud music.

Mine is mostly very high pitched and sometimes it pulses with my heart.

I can ignore it most times but if it is bad, it can drive you mad.

[frankleslie]

Phil, I used a separate 12,6 volt winding on my PT to a diode bridge, and then after smoothing to a 15 volt regulator and a 5 volt regulator. The 5 volt must be regulated and the power to op amp should also be, this to minimize hum. Maybe you can install an auxillary transformer to get the voltages, a wall wart maybe with a transformer in it that puts out around 12 to 15 vac.

[Phil_S]

Oh no! I see I've conflated the power supply requirement (5VDC) with the signal limit (1.4VAC RMS). I feel like a <unkind word of choice here>.

For the power supply, maybe I'll be able to use ss rectification to free up the 5V filament supply. Let's assume that. So, put it through a FWB and get ~7.5V, then a couple of caps with some sort of IC between them? A regulated power supply is new territory to me, or at least it seems that way. What IC? Really, I know nothing about sand.

Now, your schematic is making more sense to me. There is a regulated 15VDC supply for the Op Amp. The Op Amp attenuates or regulates the signal which first gets split off by a divider of a pair of 2.2M resistors? So the Op Amp make sure the reverb block only sees the amount of signal it can handle. Is this right?

[frankleslie]

The two 2M2 resistors are for setting up bias to the first op-amp and the two 10k are for the second. The first op-amp is a buffer with a gain of one. Check out the full schematic for PSU details.

[Phil_S]

Frank, thanks for the full schematic. I can paint by numbers now while I absorb some of how this all works along the way.