Ampeg Blueline: What's that sound?

[poisonoakie]

I recently picked up a blueline svt. When I flip it from stand by to on, there is a "wooshing" sound. There's also a hum that is constant, regardless of volume on either channel. I would love to hear anybody's opinion on what might be the source of these sounds. I'm planning on bringing it in for a full cap job and re-tubing, but was wondering if I should be bracing myself for some horrible news.

[JimmyM]

The hum could just be that the hum balance pot in front of the amp behind the grillcloth needs adjusting. Easy to do with a flathead screwdriver and ears. The whoosh sound I don't know, but sounds like nothing serious. But don't have work done on it that you don't need. Tell the tech you just want it checked out, you want the tubes tested, tell him about the hum and whoosh, and if he comes to the conclusion that you need caps and tubes, then get them. But if you tell him you need caps and tubes, you're going to get caps and tubes whether you need them or not. Tubes can last a very long time, especially old ones, and it's very rare that all your tubes will be bad. Have I had it happen to me when buying a vintage amp? Yes But no sense volunteering your money to him.

[T-Bird]

Hi.

^What Jimmy said.

The quite usual "wooshing" sound with older tube amps is IMLE the static from old components acting up on the inrush of voltage/current. I've had the sound to stop or change by changing el caps, carbon comp resistors, sometimes tubes.

The hum is mostlikely the hum balance not being what it should. My only experience with SVT was about an older CL I briefly had back in the day, and unless the "idiot lights" were both green, it hummed like a wino. It got slightly better when I put better set of tubes there, but it still needed a bit of tweaking.

A strong +1 for making sure that the tubes are in need of replacement before they're replaced. In any case, DO NOT let go of the used set without some kind of compensation. The SE guys will usually give at least á $10 for a working power tube. Over here anyway.

Regards
Sam

[One Drop]

Mine wooshed before I got a cap job done, too.

I'm in the 'get a full cap job done now but only replace the tubes if necessary' camp. My understanding is that if they haven't been replaced already enough time has passed to make it a good idea, at least to avoid it breaking down or sounding lousy on a gig, especially since the work will eventually need to be done.

[Mr. Foxen]

+1 on caps.

[coreyfyfe]

My B15 had the woosh noise before I got the cap job done as well. I think it was around $250 for a full re-cap in my SVT so brace yourself for that cost at least.

[christw]

All the bases I was going to mention were already covered: out of spec components, needs filter caps (and possibly other caps) replaced. I hope it's just the hum balance though!

[johnk_10]

the hum can also often be caused by the output tube's bias being set incorrectly (i.e. one side pulling more current than the other).

[poisonoakie]

I'm dropping it off with Mark Samson (of Matchless fame) tomorrow to have him go over the whole amp and give her any loving that he thinks she needs. Might be an expensive tune up, but I'm pretty confident that I'll have a beautiful beast of an amp when I get it back.