Squishy sound = Do I need new tubes?

[OutlawSteph1975]

I've got a squishy, rubber sound coming from my amp at low volume. You can hear it on the bottom notes. It's a Mesa Boogie F-30. I'm pretty clueless about tube amps and how to diagnose needing new tubes. I've never replaced them, and I bought the amp from a friend a few years ago who had some work done on it.

This doesn't make much sense to me either.. http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html

I tried tapping on the power tubes but it doesn't make any noise through the amp.

[Guitarslinger1]

New production (as in new foreign made) power tubes should be replaced every 6 month to 2 years, depending on how much the amp gets played. It's a good idea to go ahead and replace new production preamp tubes as well.

The tubes may, or may not be the cause of that particular problem, but replacing them is a good place to start.

[JayFreddy]

The problem described could also be caused by a speaker rub too. With the amp unplugged, if you gently move the speaker cone back and forth by hand, can you hear any noise coming from it? If so, that's probably the problem.

If not, I'd start by TESTING the power tubes (the big ones), to see if any of those are bad. Too many people neglect their power tubes, simply because they don't know any better, and power tubes are expensive.

Some not-so-nice people even put worn out tubes in amps they are planning to sell... It's always a good idea to have the tubes tested, especially the power tubes, whenever you buy a used tube amp. If/when power tubes blow, they'll usually take other components with them, so it's important to change them before they blow.

However, preamp tubes (the littles ones) can last for decades, and when those blow, they rarely take out other components, so it's safe to use them right up to the bitter end. When a preamp tube goes bad, your amp will have a noticeable loss of tone, and usually replacing that one bad preamp tube will cure the problem, so there's no reason to replace all of 'em.

Originally Posted by specialty guitars

It's a good idea to go ahead and replace new production preamp tubes as well.

I'm not sure what you mean. If you're saying the problem might be caused by a bad preamp tube, so he should replace bad and/or weak ones, then I agree.

If you're saying that pre-amp tubes, like power tubes, should be replaced every 6-12 months, I disagree.

If you're saying all new production pre-amp tubes suck, and as a general rule, you should replace those, I disagree with the general rule... There are good tubes being made today, maybe not as good as some of the NOS boutique stuff, but good enough.

While a fresh NOS Sylvania or Mullard 12AX7 will probably sound better than a new Chinese or Russian one, a fresh Chinese/Russian one will still sound better than a dead tube with a boutique label on it...

If you're going to replace Chinese or Russian preamp tubes with more Chinese and Russian ones, it doesn't make sense to just swap out everything. Just replace the ones that need replacing.

If you have a line on some good NOS boutique stuff, then it might make sense to replace the Chinese/Russian stuff, but not always...

Replace tubes that are bad or weak, starting with the power tubes. Preamp tubes can last decades without being changed. Power tubes wear out much faster. Whenever you buy a used tube amp, it makes sense to have the tubes tested.

Even if it turns out to be a speaker problem, if you've never done it before, it's probably a good time to replace the power tubes as well.

[Guitarslinger1]

Good call on the speaker rub.

Sure, new prod preamp tubes do not need to be replaced as often as new prod power tubes, but they certainly don't have the life that RCAs, Telefunkens etc. do. They are not made from the same materials, with the same coatings, or have as high a vacuum. It's just the way it is. New prod preamp tubes may last for decades, but be highly degraded for much of that time. They simply don't have the staying power that old western made tubes have/had.

That said, the reason I suggested that it's time to replace all the tubes, including the preamp tubes, is this:

"I've never replaced them, and I bought the amp from a friend a few years ago who had some work done on it."

His amp may have other issues, but it certainly needs new tubes. Start there and see what happens.

A always, YMMV.

[JayFreddy]

I think you're probably right. Sounds like he definiately needs new tubes, at the very least, new power tubes.

The rule of thumb I use for preamp tubes is, "If it ain't broke, don't fix it..."

While the older NOS "western" tubes are generally better quality than the new Chinese and Russian stuff, that's not always true.

Swapping out all the preamp tubes just for the sake of having "fresh" ones doesn't make sense to me, new production or otherwise. If you have a bad preamp tube or simply don't like the tone you're getting from your existing preamp tubes, then perhaps a change is in order.

Just change the ones that need replacing. If you've owned the amp for a few years and never changed the power tubes, that should definitely be done ASAP.

Hopefully you haven't already blown a power tube and damaged the internal circuits of the amp...

[OutlawSteph1975]

I didn't get to the store today to get tubes, but I took the grate off and found something odd. Notice the raised line bumping out near the cone like it's repaired? Is this normal? That's what might be rubbing. It's a girl's amp, btw.

[JayFreddy]

That wire is normal. It's part of the voice coil. Some speakers you can see it, others you can't. Physically move the speaker cone back and forth. If you hear rubbing, that could be part of your problem. But you'll also need power tubes, and you should expect to replace at least one 12AX7.