Are my tubes going?

[Globbits]

I was playing last night on my Laney LC-30, with the drive on 10, at just above bedroom volume, and i stopped playing and there was this modulated hissing, going up and down completely randomly and getting louder and softer. It was like a wind through trees or something. I was really freaked out...

I looked round the back, and all eight of my glass babies were glowing orange softly and healthily.

So what's going on? Is this a sign of pre/power amp failure?

(I'm looking at you, microdmititry, to help me out here! )

[bammbamm]

Any effects in the loop?

[pri0531]

Try to reseat the tubes (i.e. make sure they are in the sockets nice and tight).
Out,
GP

[Globbits]

No effects, nothing. Just guitar, lead, amp. I,m going to change my lead at the weekend to see if that helps...

[bammbamm]

I don't think that will change anything. IS it a constant rate of modulation or kind of sporadic?

Bamm

[Globbits]

It's completely random. A bit like a modem or tuning a radio...

[microdmitry]

Was it _hiss_ or _squeal_?
How loud was this noise?
Does it increase and decrease depending on how you set the master volume?
Will it hiss if you set the master to zero?
If you set gain to zero?

These things are important to know. I second the suggestion to re-seat the tubes as the first step.

Also, have you ever played your amp totally cranked?
How many channels does your amp have?
If more than one, do you hear the noise on just one channel or on all of them?

[Globbits]

It was hiss, and almost as loud as my guitar signal.
It increased with master volume just like normal guitar signal
It was as quiet as a mouse with master or gain set to 0

My amp is a Laney Lc-30. 2 channel, clean/dirty.
4x EL84's and four gain stages. I dimly recall ECC83's being mentioned.

I VERY rarely play with clean on 10, it's bloody loud! I've NEVER played with dirty above 3, as that is 10 times as loud as my drummer.

The clean channel is hiss free.

Please Help!

[bammbamm]

Sounds to me like a bad coupling capacitor somewhere in the lead channel to me. Have a tech look at it. I wouldn't reccomend for you to start poking around if you're not intimately familliar with tube circuits.


Bamm

[microdmitry]

Looks like something is wrong with the preamp. If the hiss decreases as you decrease the master volume, your problem is not in the power amp, so you can safely exclude el84's and one 12ax7 (usually nearest to them) as a source of failure.

Do you have a spare 12ax7 tube or a few? Try replacing your preamp tubes with it one by one and see if anything changes.

If nothing changes, try to locate the dirty channel tubes (even if they are _partially_ in the dirty channel). User's manual should help here. Then try pulling them one by one going from the input and find the one without which the hiss disappears. The fact that hiss disappears doesn't necessarily mean that the tube is at fault here. What we're looking for is whether it's even tubes that cause the hiss.

This, of course should be done on an amp that's NOT connected to mains and was in Off state for at least a couple of minutes. WARNING, use only one hand to pull the tubes out. Keep another hand behind your back when doing that. Make sure your hands are dry.

[microdmitry]

Excellent FAQ here:

http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html

Pretty much describes all I was going to suggest.

[lance]

I had this happen on my old Fender super twin and a change of power tubes fixed the problem. I'd say take try replacing them and go from there. At the very worst you'll have a new set of power tubes and you'll know that the problem lies somewhere else.

-Lance

[Globbits]

How much would a completely new set of 4 EL84s cost?

[Mr Orange]

I think $50 should get ya settled.

Whenever there's weird noises, change the tubes. Easy.
Like whenever it starts to smell weird, change your underwear.
That gets you pretty far in life, actually.

[Globbits]