Laney TT50H reverb dead - UPDATE

StefB

I took delivery of a used TT50 head yesterday, the second one I've owned and having had the combo too.  I have a real soft spot for these amps and love their tone and flexibility.

The amp arrived working mostly fine, but with the reverb totally dead.  It has a master reverb control and then separate dials on the three channels, all fed from an Accutronics spring tank.  I had the chassis out last night to see if any wires had come loose during transit, and all were fit nice and snug.

I've tried replacing what I am lead to believe is the 12AX7 responsible for the reverb circuit, but it isn't making a difference.  What is next to try?  I can harvest an Accutronics reverb tank from my H&K Tube 50 combo to try, but does it have to be the exact same type etc?

The amp is a clean example, from a decent private seller (300 miles away of course) and I'd like to try and get the issue fixed locally as inexpensively as possible if a DIY solution is available, having already paid slightly over the eBay going rate for a clean, well looked after example.

The seller tells me the reverb was working fine on testing before boxing the amp up, and he did package it well.

Any advice you knowledgeable chaps can offer will be most gratefully received...

Schematic here - http://www.tremolo.pl/Firmowe/LANEY/TT50H.pdf

Manual here - http://www.audiotek.sk/produktyGTA/laney/laney_tt50600px_p1.pdf

 

jpfamps

Most likely a problem with the tank, which could have been damaged in transit.

If you have a multimeter you can test the DC resistance of the tank. Depending on which tank it is it will have an input resistance of 1-40 ohms and and output resistance of 200 ohms.

If either of these are open circuit then the tank is faulty. Sometimes it's simply a case of repairing a broken wire in the tank, but it could also be that the wire in the (usually output) transducer has failed and a new tank is required.

crunchman

If it is dodgy it's worth opening it up to have a look.  I fixed a tank that was just a matter of soldering a wire to a connector where it had come away.

ICBM

Unfortunately most modern tanks don't break in an easily-repairable way, but it's still worth a look. You can find out if it's the tank first by unplugging the cable from the Output end and touching the tip of it with the amp on and the reverb turned up a bit - if you get a noise the return amplifier is working, but if you don't get reverb crash with it plugged back into the tank and shaking it, the tank is dead.

StefB

@jpfamps @crunchman & @ICBM thanks for taking the time to help me out with this.

I stripped the amp down last night and followed all your suggestions, apart from @jpfamps multmeter idea as I don't have one.  My self-diagnosis is that the tank is dead as it didn't respond to any of the suggestions @ICBM offered.  To my untrained eye there doesn't look to be anything physically wrong with the tank, but I guess there must be.

Moving on to the question of sourcing a replacement tank while I have the amp in bits, while the model number remains the same (4BB3C1B), the colour and look of the current tank available are different:-

http://i1085.photobucket.com/albums/j437/stefbillington/Misc/WV_zps62b24581.jpg

Watford Valves have these in stock for a reasonable £22.50 + P&P - http://www.watfordvalves.com/product_detail.asp?id=1253

I have found what looks to be NOS of the exact same tank currently in the amp however, which looks like this:-

http://i1085.photobucket.com/albums/j437/stefbillington/Misc/ebay_zps2127fd13.jpg

These are available on eBay UK for £30.40 delivered (http://www.ebay.co.uk/itm/360818603092?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT), so a little bit more but perhaps worth it for an identical like for like replacement, or will the black on do the job too?  I'd prefer to buy from Watford Valves.

Finally, the tank in the Laney has the red & black leads for connection to the amp soldered to the input and output already.  Will a new one come pre-wired, or will I have to remove and attach the leads from the goosed tank?

ICBM

The lower picture there illustrates the problem with modern Accutronics tanks - the white push-connector on the transducer bobbin. This is heavy enough to vibrate and it then breaks the extremely fine coil wires where they're soldered to the pins it pushes onto, which can sometimes be repaired but is very tricky.

In other words, don't buy that tank! The new black one may have the same issue though. If you want to be thorough, once you've checked it works, cut off the push-connector and solder the wires directly to the pins, as close as possible to the bobbin. That prevents the problem - although it does invalidate any warranty on it, so you may not want to do that.

The cables unplug from the tank, you don't need new ones.

StefB

Thanks again for that @ICBM ;

If I don't buy either of the tanks illustrated though, what other options are there? Also, will it be safe to use the tank from my H&K Tube 50 with the Laney to satisfy myself once and for all that the issue is with the tank? 

Presumably it would be safe to buy a different model, but Laney would have chosen the one installed because it was tuned to suit the type of amp/versatility they were going for with different levels available for each channel etc?

ICBM

You need to be a bit careful because the input impedance varies - ones designed for valve drive have a lower impedance than for typical solid-state drive, so if you use the wrong one you can overload the driver IC in a solid-state reverb. I could be wrong but I think both these amps have solid-state reverb though, so it should be ok just to try it.

StefB

The fault was eventually diagnosed as the tank itself, and a new one has today arrived from Watford Valves.

Final question please @ICBM - does the quality of the RCA lead I use to connect the new tank matter too much, or will a standard 1m cable for a couple of quid be fine?  The cable attached to the defective tank is soldered onto the terminal ends and so doesn't have phono jacks that can be connected to the new tank.

Easier for me just to source a new one, so does the quality of the lead matter?  Cheers.

ICBM

StefB said:

Easier for me just to source a new one, so does the quality of the lead matter?  Cheers.

No .

StefB

Thanking you! :-)