[SOLVED] not a tube problem (Club 40 tube problem ?)

[LGM]

Hello

My son plays on a HT club 40. It performed flawlessly, no hiss no buzz, perfect for a year or so.
Last Saturday I took it out for a rehearsal session outside of our house, and let a fellow guitarist use it for two hours.
But when we plugged it back in our house, it gives an awful noise.
I suspect one of the tubes got damaged during transport ... although we took great care.

Anyways, I need to fix it ASAP (!) because my son hates me.

Symptoms: loud RRRRRRRRRRRRRR noise when I plug a cable in the input jack, louder when I increase volume, noise on both channels (clean/overdrive), louder on overdrive. No noise when no cable is connected. Same noise with or without a guitar plugged on the other part of the cable. No pedal involved.

My "guess" is a preamp tube failure, any other suggestion would be really appreciated.

Is there a diagnosis procedure I should undertake to nail down the bug ?

What are the OEM specs of the tubes ? The owner manual states ECC83 but there are tons of brands .. I'd like to replace the faulty tube (if any) with the exact same reference ...

Thanks
(sorry if my english is not perfect I'm french)


EDIT: no noise in stand by mode, 3 different jack cables tested with same result (noise).

[thephantum]

First of all, if the amp is only a year old it should still be under warranty. I believe the EU warranty is something like 3 years, so before you start opening up the amp yourself (thus voiding that warranty), make sure your warranty is expired...

The noise you are describing sounds like some kind of arcing or short. My first guess would be tubes since they are a wear and tear part. However, because it's in both channels, it may not be a preamp tube.

To start, you can try swapping the two preamp tubes. It's not a definitive test because of how the preamps work in Blackstars, but if the noise goes away in the clean channel and stays in OD, the tube you just swapped to V2 is bad. If the noise is still on both channels, the issue is most likely not in the preamp tubes (but they are not ruled out either).

I would try putting in new (or known good) preamp tubes. Any ECC83/12AX7's will work. Depending on when the amp was made, it might currently have Sovtek's or TAD's, but you will not do wrong putting TungSols or Mullards in as they are better sounding tubes. Preamp tubes are plug and play, so no other adjustments are needed. Just pop them in and go.

If it's not a preamp tube, the next likely culprit is a power tube. In that case the pair should be replaced and, even if you put the exact same brand in, the amp will need to be properly biased. You can however, pop in a new set to see if the noise goes away. If it does, then just take the amp to be biased and your set. If it doesn't, it needs to go to a tech to get diagnosed.

[LGM]

Hello thephantum, thanks for your reply.

We bought the amp second hand so I don't know how old it is and I don't have any warranty certificate .. my message was not clear about this, sorry.

I tried to remove the back cover of the amp but it is totally stuck, no way I can even make it slightly move !
I will have to bring it to a service shop ... bad news for my guitarist son.

Regarding the pre amp tubes, I will follow your advice and if a replacement is needed I'll go for one the brands you quoted if they are available here.


Suggestion for Blackstar techs: why don't you design your amps with an easy access for replacing the tubes ??? Might not add to much cost and would be really helpful.

[thephantum]

Well the good news is that, since you got it used, it's even more likely to be a tube problem.

The back will come off. What's happened is that continuous heat cycles have caused the tolex on the amp and panel to stick together, so the panel puts up a fight. Slowly and carefully working around the edges with a smaller screwdriver will get it the panel off. It just takes some patience to make sure you don't damage the tolex with pry marks.

Once you get the panel off, the tubes will be hanging there right in front of you....very easily accessible.

[LGM]

Hi,

I eventually found a solution ...
It turns out there was a bad welding inside the guitar, which somehow put the amp in a bad state (electric charge or whatever) and produced the noise, which was still audible even after I would unplug the guitar and let the amp off for 48 hours !
I fixed the guitar, plugged it back in and the noise was gone.

Anyways, I have an appointment with a tech next month for a full maintenance on the amp, which will do no harm !

Thanks for your support thephantum.

[thephantum]

Glad you got it sorted out.