AC30 needs retubing

[dlybrand]

Hey everybody! I just got a new AC30 today, and the first thing I got when I plugged it in was an awful rolling hissing sound, like waves on a beach followed by a loud 'pop'. The sound gets louder when the master volume is turned up and disappears completely when the master volume is turned all the way down. From what I've read about tube amps, this means I need new tubes.

However, I don't know how to go about finding which tube needs replacing. If anyone could give me some advice, I'd appreciate it.

Also, I have a recording of the sound the amp makes if anyone knows where I can upload mp3 files.

[Gtr_tech]

Could be tubes, could be caps, could be cold solder, could be resistors....could be anything. Can you make the noise come and go by whacking the amp? That narrows it down to tubes or solder.

[dlybrand]

I can't alter the sound by hitting the amp, but I can now see that one tube is not lit up when the amp is on. I'm guessing that's the tube then.

[Gtr_tech]

Maybe, maybe not. swap the tube with one of the same type to see if the heater lights on that one. If not, its connections at the socket that are the issue. If this is one of the newer "cc" versions then its got pcb mounted tube sockets and they are prone to cracking loose from the board.

[Chuck H]

FWIW it could also be a dirty tube socket or pin. I have found this to be the case a couple of times with these symptoms. It could also be why the tube isn't lighting up. I'd try a known good tube in that socket and if that doesn't fix it try cleaning and retentioning the socket. If that doesn't do it I would check for broken traces on the board for that socket.

Chuck

[tubeswell]

Having said all that, hissing, crackling, popping are classic symptoms of output tube decline.

Your garden variety EL84s are typically the least resilient of the widely-available crop of current production output tubes, and typically need replacing every 12 months (depending on your frequency of use). pop in a new quad and see. (You should keep a spare quad handy anyway, so its worth splashing out for)

[dlybrand]

Thank you for the replies, everyone. I have another question, though: should I go ahead and try to sort this problem out myself or should I just return this amp for a refund since it was faulty out of the box? I can't exchange it for a new product because it was 'blemished' and therefore marked down, but I could spend a few extra bucks and just get a new one which presumably would work properly.

[pdf64]

I would geta quote from tech and base you decision on that. But if it's new as in brand new, can't you get vox to help out?
If the noise disappears with the master vol turned down, I reckon it is extremely unlikely that the fault is the output tubes (el84). Peter.

[6267]

I've had the "ocean" sound start on amps with bad preamp tubes, swapping fixed it...although I wonder if the "blemish" is that the socket cracked off the PCB too...mighta been dropped?