Reverb no longer working

knuckleberryfinn

I built a Vibrolux Reverb recently and the reverb has just died. It's definitely the tank (I've checked the valves and the cable and tried the tank with another amp). The connections to the sockets and transducers appear to be fine, but there's a bit of brown leaky stuff on the tiny input transducer socket. Has the transducer burnt out? If so, what might have caused it? The voltage on the reverb transformer is high (440v I think - can't quite remember) but this is the same as a Pro or Twin Reverb, which use the same value components I think. Any help would be greatly appreciated.

ICBM

Does it have the push-on plastic jumper blocks on the reverb transducers?

If so, cut them off and solder the wires directly to the pins. Do the output end first and then test it, it's always this end that breaks. If it's not that, it's probably broken the fine wires on the red plastic bobbin and is almost unrepairable.

You can check which end is faulty even if you don't have a meter - connect just each end at once to the return cable (the one that goes into the output jack on the tank) and shake the tank with the amp on and the reverb turned up - if you get reverb crash that end is fine; you'll get less crash from the input end but still some.

The brown stuff is flux residue, not an issue or a sign of anything worse. While the reverb transformer does have a high voltage on the primary (valve) side, the secondary (reverb tank) side is a low-impedance winding and never produces high voltages.

If it's an older reverb unit that you used and has wires that go directly into the coils, it may be dead anyway.

knuckleberryfinn

Yep the input side is fine, and the output buggered. What a pile of crap - it's only 6 months old. Is it possible to replace that bobbin or rewind/connect it so it's more roadworthy? I don't really want to spend another 30 quid on a tank of the same quality (it's an accutronics/belton one). If it can't be fixed, is there a more hardy alternative to accutronics?

ICBM

If you're incredibly careful and lucky, you can scrape the coating off the wire where it crosses the bobbin, solder on a new piece of wire and reconnect it to the pin. I used to try it on every broken one at first, but the success rate was only about one in three or four so I gave up trying, it's quicker and hence cheaper if it's on my job time to replace the tank.

If you catch it before it breaks, cutting off the jumper block and soldering the wires to the pins as close to the bobbin as you can stops it breaking - I'm pretty sure it's the mass of the jumper vibrating which flexes the pins and breaks the wires. It's a terrible re-design purely to save money - the old tanks were far more reliable, and almost only ever broke at the RCA jack end, which is easy to fix.

Beltons and other even cheaper Chinese-made tanks are much more reliable than Accutronics now - sad but true. They don't sound as good though.

There is a reason why I'm always happy to pay at least a tenner for old knackered amps with reverb tanks in, if the reverb is still working...

knuckleberryfinn

Thanks ICBM. I'll try the fix after Christmas and hopefully I'll get lucky. I did research new tanks before buying this one and the verdict was pretty universal - no one is currently making a good reverb tank. Very annoying. I don't suppose you know if Mouser or Farnell stock transducers which can be fitted in some ingenious way?

exocet

The tanks sold by TAD are pretty good. They are built like the old Accutronics units. I think Belton now make the Accutronics badged units.

knuckleberryfinn

Fixed it! I had a spare twenty minutes so picked at the tiny copper wires, which broke in a convenient place. Soldered some solid wire from the pins to the transducer and back in business. Hopefully it will last.

knuckleberryfinn

I was going to ask about TAD. They seem to be the only alternative to accutronics. Thanks for the info.

ICBM

knuckleberryfinn said:

Fixed it! I had a spare twenty minutes so picked at the tiny copper wires, which broke in a convenient place. Soldered some solid wire from the pins to the transducer and back in business. Hopefully it will last.

Well done! I fixed the first one I tried too. The trick now is not to assume they will all be fixable .

I hope you got rid of the jumper blocks as well...

knuckleberryfinn

On one side yes. I'll do the other as soon as I get a minute - hopefully before it breaks irreparably. Cheers!

martinw

exocet said:

The tanks sold by TAD are pretty good. They are built like the old Accutronics units. I think Belton now make the Accutronics badged units.

Yes, Accutronics and Belton are now one and the same:   http://www.accutronicsreverb.com/

ICBM

martinw said:

Yes, Accutronics and Belton are now one and the same:   http://www.accutronicsreverb.com/

It's unfortunate that - if the pics are correct - they've gone with the new Accutronics construction and not the older Belton construction, which was more reliable.

I assume there just isn't enough demand for spring reverb tanks to support two separate companies now.

Personally I now prefer digital reverb for all but top-end traditional valve-driven circuits. It's more reliable and sounds better than a cheap spring, and is probably cheaper too.

martinw

+1 on all that.

I do both a 1 valve and 2 valve spring reverb option on my amps, but for the future I'm also working on adding a digital reverb option using the Belton 'brick'.

It's used in some very well respected reverb pedals (I've got one, a Juansolo job, and it sounds amazing.)

knuckleberryfinn

I want to try designing a small 3 to 5 watt push-pull amp and was wondering how to get reverb into it.. Would the Belton brick be the best way of doing it do you think?

ThePrettyDamned

martinw;111835" said:

+1 on all that.

I do both a 1 valve and 2 valve spring reverb option on my amps, but for the future I'm also working on adding a digital reverb option using the Belton 'brick'.

It's used in some very well respected reverb pedals (I've got one, a Juansolo job, and it sounds amazing.

Poodle pedals does a simple pedal using the belton brick. Supposed to sound great, and there are several modded versions available in the right circles, so it's a great place to start

I'm a fan of digital verb and delay. Less noise, better tones (mostly). My bandit has a long spring tank and it sounds pretty good, if a bit bright. It doesn't get clangy until the last quarter of the dial though, so perfectly usable, if not exactly a digitech hardwire.

jpfamps

Wampler also use the Belton brick.

I bought one a while back, but never got around to doing anything with it....

jpfamps

knuckleberryfinn said:

I want to try designing a small 3 to 5 watt push-pull amp and was wondering how to get reverb into it.. Would the Belton brick be the best way of doing it do you think?

You will need to derived a power 5V supply for the Belton brick (I would advise not doing this from the filament supply), and then work out how to send signal to it and how to amplify the return signal and mix it with the dry signal.

If you wanted to do this using solid state parts, it would be better to have another power supply rail as well as the 5V, eg 12V or better +/- 12-15V.

It's eminently doable though, and would make for a nice project.

knuckleberryfinn

That sounds more complicated than I'd expected. What's wrong with a 5v filament supply - too high current?

jpfamps

knuckleberryfinn said:

That sounds more complicated than I'd expected. What's wrong with a 5v filament supply - too high current?

The filament supply is not too high current; the current rating is more an upper limit that a winding can deliver at it's rated voltage. If a device/s connected to it draw less current that this then there no issues.

You can rectify the filament supply which will give you around 8-9VDC which can be regulated down to 5V.

This will work, but the problem is if a valve shorts out to the filament supply and imposes the HT on the filament supply. It's unlikely that any circuitry connected to the supply would survive.

You best bet would either to find a transformer with suitable primary windings so you can generate the necessary voltages, or to uses an extra mains transformer for this function.

ICBM

jpfamps said:

You can rectify the filament supply which will give you around 8-9VDC which can be regulated down to 5V.

This will work, but the problem is if a valve shorts out to the filament supply and imposes the HT on the filament supply. It's unlikely that any circuitry connected to the supply would survive.

Could you prevent that by fitting a very big Zener diode (say 10V 50W) across the rectified supply, and an HT fuse? The fuse should go before the diode, even with a direct short in the valve. Not that cheap a component, admittedly.