Hiya guy,

I have a strange problem with my Blackstar HT40 which I can't work out.

When I power up on standby for the tubes to warm up, after about 90 seconds with the amp still on standby and nothing plugged in it starts to crackle, like static noise, similar to the noise if you unplug your guitar with the amp still on. Even if I turn the volume completely off it still makes this noise. It'll just keep getting louder until it pops and thats it it stops and the amp is fine. If at anytime I turn the standby off (ready to use) the noise stops.

Then say in a rehersal or gig it'll start to crackle again quietly when I'm playing but it's not really an issue unless I switch it to standby.

Any ideas?

I had the same problem with my peavey and it turned out to be one of the tubes that arched an made a short circuit. Replacing the tubes should solve your problem
Cheers, I have just taken out the 2 EL34's and cleaned the pins, it does seem quieter but I just noticed that one of them is glowing a lot brighter than the other?
Yes mine did the same thing.The one that's dimmer is probably faulty, but it's best to replace both as they are matched
thats really strange since those amps shutoff the output as soon as you turn the standby on, unlike other amps where it gradually quiets.
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I've had the same problem, it was caused by a bad tube in the preamp, swapping it with a new tube solved it. Borrow some tubes and try.
Cheers guys, I've ordered 4 new tubes and they should be here in a few days. Fingers crossed.
Cheers guys,

Unbelievably my tubes came today from guitar-valves.co.uk!

I replaced the pre amps first as I suspected these were the problem, fired up but soon after the crackling started, anyway, I had a quick play and what a difference the Tungsols made, much more clarity, sharper with awesome bite which the low end compliments perfectly. Normally I only play rhythm on the bridge PU because on the neck it just turns mushy but these babies give the neck PU a whole new lease of life.

Anyway power amps next and bingo, problem sorted, I played and the amp as just gained about 20% in volume and punch is awesome! I haven't biased tho but it sounds ok, I suppose it was a straight swap like for like?

I feel sorry for the neighbours because these puppies are gonna have a thrashing later!

Replacing dying power tubes like buying a whole new amp isn't it? What valves did you used to have in there? I'm not that keen on TungSols myself but they'd be definite step up from say, Sovteks - even though they out of the same factory.

Sorry I didn't jump in here earlier. Once you'd cleaned the pins the answer was obviously power tubes. You could have tested that by pulling pairs but as soon as you said they lit up completely differently now, the answer was staring you in the face.

Edit: oh, 40W. So only two EL34's - you can't pull pairs.
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Last edited by Cathbard at Sep 10, 2011,