#1
Hey

I was at a band practice today and my Laney VC30 decided it was going to start making these really harsh, nasty screeching noises at random occasions.

this is not feedback, it happens at any volume, even when turned down to 0, and even then it is very loud, but only if a guitar is plugged in - i have tried different guitars and cables, the high and low inputs, etc and it still happens. It was fine last sunday when i last played through it at home and at bedroom volumes, but when i got it to the rehearsal space today it just made these awful noises straight away.

Does anyone know what this problem could be and how i would go about fixing it? i have a gig in 2 weeks and need it sorted quickly if i'm gonna be able to use this amp.
Rig Winter 2017:

Fender Jazzmaster/Yamaha SG1000
Boss TU-3, DS-2, CS-3, EHX small stone, Danelectro delay
Laney VC30-112 with G12H30 speaker, or Session Rockette 30 for smaller gigs
Elixir Nanoweb 11-49 strings, Dunlop Jazz III XL picks
Shure SM57 mic in front of the amp
#2
I think a tube is microphonic, but that's all I can think of... try the pencil tapping test.
#3
Sounds like either the guitar is picking up interference from something in the area or you have a problem with the pickups or wiring. You should try a different guitar in the amp and see if you have the same results, if the noise is still there then it`s something with your amp.

Don't take my word on it though I'm still new to this stuff, but seeing as it's only a issue you have with a guitar plugged in it would make sense.
#5
My guess would be a microphonic tube. Turn on the amp and tap each tube gently with a pencil. It is normal to hear the tapping come through the speakers to some degree but it shouldn't be loud. If one has gone microphonic it'll be obvious. Tap gently, not because the tube might break but so that the vibrations won't travel down the chassis and set off the one that is actually faulty. I've been tricked like that before. Just tap each tube very gently.

You should have at least one spare preamp tube. Trying your spare in different positions until the fault goes away is another approach.
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Cathbard Amplification
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Last edited by Cathbard at Nov 20, 2011,
#6
Quote by Cathbard
My guess would be a microphonic tube. Turn on the amp and tap each tube gently with a pencil. It is normal to hear the tapping come through the speakers to some degree but it shouldn't be loud. If one has gone microphonic it'll be obvious. Tap gently, not because the tube might break but so that the vibrations won't travel down the chassis and set off the one that is actually faulty. I've been tricked like that before. Just tap each tube very gently.

You should have at least one spare preamp tube. Trying your spare in different positions until the fault goes away is another approach.

i just tried this and none of the tubes seemed microphonic, but after a couple of minutes the amp started making the same screeching sound as well as a loud popping sound, and one of the power amp valves was flickering whenever the popping sound happened and glowing a little brighter while it screeched.

i can only assume this means i need to replace the power amp valves?
Rig Winter 2017:

Fender Jazzmaster/Yamaha SG1000
Boss TU-3, DS-2, CS-3, EHX small stone, Danelectro delay
Laney VC30-112 with G12H30 speaker, or Session Rockette 30 for smaller gigs
Elixir Nanoweb 11-49 strings, Dunlop Jazz III XL picks
Shure SM57 mic in front of the amp
#7
Yes it may very well be a bad power tube.

If you have an extra set pop em in there and see if that works.
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Morley Bad Horsie 2
MXR Smart Gate
#8
Quote by Robbgnarly
Yes it may very well be a bad power tube.

If you have an extra set pop em in there and see if that works.

yep, i've put the stock power tubes back in the amp and it's fixed the problem.

the only thing now is i remember why i swapped out those tubes in the first place - they produce a lot of hiss and have a bit of a brittleness in the top end, but for the time being it's better than having a tube that's on the blink
Rig Winter 2017:

Fender Jazzmaster/Yamaha SG1000
Boss TU-3, DS-2, CS-3, EHX small stone, Danelectro delay
Laney VC30-112 with G12H30 speaker, or Session Rockette 30 for smaller gigs
Elixir Nanoweb 11-49 strings, Dunlop Jazz III XL picks
Shure SM57 mic in front of the amp