Silent amp

fnpt

So I left my laney cub12 turned on overnight and this morning it was totally silent. Any clues as to what might be the cause? Cheers

ICBM

The usual cause is a thermistor in the valve filament supply. They very commonly fail.

fnpt

Thanks @ICBM. Does that mean that replacing the faulty valve will solve it or is there any additional work to be done?

ICBM

fnpt said:

Thanks @ICBM. Does that mean that replacing the faulty valve will solve it or is there any additional work to be done?

No, you need to replace the thermistor. It's soldered onto the PCB so it's not really a DIY job unless you're familiar with that sort of thing. The valves themselves are probably fine.

It's easy to check for it - if none of the valves light up, it's almost certainly this.

fnpt

 That's a bummer. The valves do not light up in fact. Thanks @ICBM.

Voxman

Mine had this overheating/cut-off problem and Laney fixed it under warranty.  First thought, if this is the thermister resistor:

• When did you buy your Cub?
  
• Where did you buy it from (some stores give their own free warranties eg DV247, 3 yrs)? & 
• Did you register on-line for Laney's free 5 yr extended warranty?

  Even if its not under any warranty, have a chat with Laney (Headstock Distribution Ltd, tel: 0121 508 6666). This is a known problem with these amps and they might be prepared to fix it for you at no charge, or at least send you the upgraded replacement part free.

DJH83004

You can actually get a small 20mm fuse holder to fit into the PC once the thermistor is removed, with a bit of 'adjustment' to the pins, but best left to your amp tech to be honest.

DJH83004

Looking back at my notes & photos, it looks like I had to put small leads onto the fuse holder and into the PCB (shown minus the plastic fuse cover)

ICBM

It's a poor design really. The only reason I can think of why they would use a thermistor in the first place is because the transformer isn't quite beefy enough to supply the full valve current continuously - and I have come across a couple of failed ones too, so that doesn't seem unlikely. Apparently they originally used a fuse, but presumably - like all filament fuses - they had too many nuisance blows unless the value is high enough that it doesn't really do a lot…

I've replaced a couple of them with a wirewound resistor - from memory 0R1 2.5W, but I would need to check - that only knocks off about a quarter of a volt from the filament voltage and will limit the cold-valve current to some extent, but in the event of a real short the resistor would burn out before the transformer. I'm not normally a fan of using resistors as fuses, admittedly.

DJH83004

Never been a lover of thermistors, I have seen too many blown to bits, when something upstream goes short circuit. Most amps don't have any protection in the heater circuit other than the transformer primary fuse. A sacrificial resistor is a good idea but if they go, they can make a bit of a mess on the PCB, but equally I agree fuses can be troublesome with nuisance blows on in-rush current. Leo didn't worry too much, but then again his transformers could power half of Yorkshire!!
  

fnpt

I bought the amp from Thomann around 5 years ago. I suspect the warranty has already expired. I'll contact them anyway and if that doesnt solve it I'll try the people at Laney. I'm in Portugal however so will still have to look for a tech to do the job. 

fnpt

Bumping this thread because I've turned the amp on again and it played for about 5 minutes before it slowly decreased the volume and went off again. Tried it a few minutes later again and the same thing happened.

Having read this: http://www.soft.com.sg/forum/showthread.php?222341-Is-your-Laney-CUB12-10-dying-after-a-couple-of-minutes-Read-This! do you think that it is safe/ possible to solve the problem by bypassing the thermistors?

ICBM

If you don't mind risking the power transformer failing at some point then it's safe to bypass the thermistor. Given that Laney transformers quite often seem to fail anyway you may either consider that increasing the risk, or simply making it no worse…

fnpt

Thanks @ICBM. You see, I like my Helix more everyday...

57Deluxe

is that vintage silent or more modern silent?

fnpt

I finally contacted Laney about this and in less than 24 hours they had already agreed to send me a replacement part. Great service from Laney.

I just need to find someone local qualified to fit the new thermistor.

ICBM

fnpt said:

I finally contacted Laney about this and in less than 24 hours they had already agreed to send me a replacement part. Great service from Laney.

I just need to find someone local qualified to fit the new thermistor.

This is a very long shot, but seeing that you're in Portugal…

So is the chap who makes these, and he can clearly solder.

http://www.ebay.co.uk/itm/Guitar-Amplifier-Attenuator-Volume-Pedal-Passive-Volume-Amp-Reducer-/141620893968?hash=item20f9435910:g:tG4AAOSwKtlWk9Ft

I'm aware that Portugal is quite a big country .

fnpt

Thanks @ICBM. That guy is in Aveiro, north of Portugal whilst I am in Madeira. It would involve shipping to and fro.

ICBM

fnpt said:

Thanks @ICBM. That guy is in Aveiro, north of Portugal whilst I am in Madeira. It would involve shipping to and fro.

Ah . I did think it was a long shot!

Madeira is a lovely place - I've only been once, about 25 years ago, but I am now slightly envious .

fnpt

Its time to return then - things are quite different from 25 years ago but still a nice and convenient place to vacation especially if you have kids. Easyjet flies here from Gatwick.

ICBM

If we hadn't been on holiday already this year I would suggest it to my wife and just not tell her why I'm putting a soldering iron in the suitcase .