Is your Laney CUB12/10 dying after a couple of minutes? Read This!

Laney CUB12R - Flickering Power Lamp , amp dies after 2 minutes
I have got two Laney CUB12R amps. I use them as a stereo setup and really love the tone they pump out.

The other day, at very low volume, one of the amps just shut down. I knoticed the power lamp flickering, then the amp shut down. After resting for 5 minutes it can power on, but will shut down again after 2 min...

FYI: Swee Lee is TOTALY CLUELESS and and of no help whatsoever with this problem! I really hate that shop!

Anyway, I did a bit of reasearch, and to make a long story short, Laney had a bad batch of Polyswitch thermal fuses that made thier way into the CUB12R. The component is easy to replace with a soldering iron. Only issue, not stock of this part in Singapore.

I have ordered 10 pcs of the polyswitch from the US. If anybody else is having a similar problem, I have extra components avail (See Below for more details...)

Good news: I have replaced the thermal fuses and the amps are working fine now. Been running them with an MP3 player for several hours now and no problem

Take note:

1) The replacement thermal fuse is a bit smaller than the original one used, but it is the same part (different manufacturer)

2) my lamp still flickers during warm up. To be honest, the flickering might just be normal behaviour for these amps and I just never noticed before. Anyway, as said, with the new thermal fuse, amps are sounding great again!

3) I had to remove the tubes and tube clamps in order to remove circuit board to be able to access the component. Make sure you let amp sit unplugged for 1 hour before opening to avoid electric shock from capacitors. Also, be sure to put a dab of paint on each tube clamp screw upon reassembly to avoid any 'microphonic' effects.

Total repair time was about 10-15 min per amp. Tools required:
1) soldering iron
2) solder sucker and/or solder wick
3) Good quality electronics solder
4) small cross screw driver

I'll leave the extra thermal fuses at my pub if you wish to but one or two. The pub is O'Bama's Irish Pub located at 54 Tras Street. Very near to Tanjong Pagar MRT. PH 62551090.
You can go by any day after 4PM.

Regards

laney cub 12r, burning hot Power transformer

Hi thanks for the tip.

I have a laney cub 12r here in europe.

My problem is that the power transformer runs to hot after 1.5 hour of idle with no playing (can't hold my hand on it for more than 1 second), even when the amp is biased dead cold (-14,5V), with different sets of EL84 tubes eliminitaing excessive heater current draw form one particular tube.

It has not shut down yet as I have turned the power of when the PT was getting super hot.

I have had the amp on without any tubes plugged in and the PT just got slightly warm (not hot) after two hours.
The pilot light connected to the heater current line flickers some with tubes plugged in, but is steady as a rock without tubes plugged in.


Can a faulty thermal fuse connected to one of the heater lines (3V) give problems in voltage balance and heater current draw from the PT ,, stressing it and heating it up gradually over time..

I read that one guy had a problem with his cub 10 dying down after 10 minutes of playing loud.
His solution and he quotes :
thermal fuse...
And I got the solution ...
"a variable tagged TR2 pot inside... turned it off (fully counter clockwise) and ...
BINGO!!! Perfect sound again ... i've been playing loud since i woke up this morning... "

This is a hum balance pot in the cub 12r between the two 3V heater lines, i assume it the same in the cub 10 .
Not sure what he did that solved his problem ??

Maybe turning it fully counter clockwise he somehow bypasses the 3V path that goes through the thermal fuse.??

Hi

For ref, a CUB10 schematic link is here:
http://music-electronics-forum.com/attachments/13144d1300228974-cub-10-2009-.pdf

Pretty similar to CUB12.
You can see the thermal fuse (aka poly switch) down by the hum control part of the circuit (PTC6.0).

The thermal fuse is either closed or open. So I don't see how that could be causing the problem you are describing. Also, I don't believe you tube's heaters are the source of the problem as if they were drawing excessive current, the 6amp rated thermal fuse would shut down.

I would suggest checking the impedance of the internal speaker and also trying an external speaker to see if you still get the heating effect Tube amps as a rule don't like high impedance loads (opposite of transistor amps) and that is a common source of excessive tube power consumption.

As for tweeking the hum pot all the way, it would ground one side of the heater and the other would be on 1 side of 3v AC. this may allow the tube to function with an open thermal fuse, but would result in excessive hum as the 'AC hum cancellation' would be gone.

Flickering power lamp is common/normal on these amps and is not a concern in itself.

Also, for bias, best to set to the factory default setting (-21v) unless you have access to a tube tester and can acurately measure the bias curves of the tube. Improperly biased tubes will affect sound quality and power efficiency.

Hope that helps mate

hi again

To some extent...

I got a bias probe and I set the EL84 in my cub 12r to around 22-24mA at idle. THe bias voltage is all over the place for different tubes as different EL84 can draw very different amounts of current at a given bias setting.

I have tried different EL84 but the PT still warms up to painfully high levels after and hour or two at idle with maximum bias voltage (-14.5V for the cub 12r) less than 15 mA draw from each tube. http://www.webervst.com/tubes1/calcbias.htm

My amp is modified with a 8K primary quality large output transformer with an 8 ohm speaker on the 8 ohm secondary. I tried both the internal 8 ohm speaker and an external 8 ohm.

The only difference i can tell between the OT's is that the small resistance from the center +B pin to each side is slightly lower for the upgrade output transformer than the stock transformer. (104 ohm -116 ohm stock , 79 ohm - 98 ohm for the upgrade). The difference between the two sides is perfectly normal and reflects the way the transformers is wired..

Regarding the "Flickering power lamp is common/normal on these amps and is not a concern in itself."
When i unplugged all the tubes, the pilot light seemed stable, with the tubes in drawing current from the heater current line, it dims, comes back at times but mostly seemed dimed. I will see if I can secure the lamp better in its socket.

I have had the power on once without the speaker connected, which was a small glitch from my side. I had all the controls turned to zero, and it was only for a shorter duration of time. I observed no strange things. I turned of and touched the OT but could not detect any heat from that...

Oh , and the cub 12r will draw more heater supply than the cub 10.

3x12ax7 + 2xEL84 = 2.5A
2x12ax7 + 2x6v6 = 1.75A

When i get hold of the stock output tranny (it is at the repair shop, i had a diode go bad in the relay system of the cub 12r) I will try that again, and see if the upgrade tranny is making things fishy.

ANother guy from down under has also mentioned his PT in the cub 12r getting very hot after a while at idle. And his is a stock amp. But then again, if he does not have a clue on his bias voltage , chances might be that he is just running it to hot. My amp was biased totally wrong out of the box. (with stock tubes should be -12.5V to - 11.5V, mine was ~ -7V) drawing probably way more than 35 mA pr tube , which caused tubes and power transformer to heat. This was before the upgrade OT.

thumbs up for sharing + offering help

I had this happen to me, brought to Swee Lee Service center and the tech there knows of this problem. Talked to him for a little bit and he said he'll just bypass the thermal. Its safe and it won't act up again..

This was back in November and till now, after the service, amp is fine no cutting out whatsoever. Brought to a jam and connected a 4x12 running volume on 10 for 2 hours, still fine

But thanks for the info. Its a common issue, just don't know why Laney didn't detect it earlier.

Hi there, my name is Jonathan. I'm from Surabaya, Indonesia..
I have same problem with you.. I have 1 Laney cub12r and 1 laney cub head. Both of amp dying after 5 second. All Tube turn off.. What wrong with this amp? Fuse also?
How much price for the fuse? May I ask your WhatsApp number? Thx

Jonathan Arfian said:

Hi there, my name is Jonathan. I'm from Surabaya, Indonesia..
I have same problem with you.. I have 1 Laney cub12r and 1 laney cub head. Both of amp dying after 5 second. All Tube turn off.. What wrong with this amp? Fuse also?
How much price for the fuse? May I ask your WhatsApp number? Thx

Click to expand...

Hi Jon, I hope you are aware that this thread is more than 4 years old and OP may not be active on this forum anymore.
Hope that someone is able to help you out or perhaps you would like to try
https://www.facebook.com/GworX.sg/?ref=page_internal

All the best.