• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Noise from SVT Classic — help identifying?

T

Teabag41

Dec 5, 2025
4
6
#1
Hi all — apologies for hastily creating an account, but I have a specific question that's pretty time sensitive. I'm a looooong time lurker here, and this is the first time I've had a problem specific enough that I couldn't find an answer from anyone else who'd already had it.

Have seen this SVT Classic for sale at a decent price (if there are no really major defects...) but the owner says it has a noise issue. They sent me a quick video to illustrate. Any quick takes or questions I should go back and ask? The obvious one for me is whether or not the noise is coming through the speakers, sort of sounds like a noisy fan to me (and maybe gets louder round the back?) but I've never owned one of these.

Any and all thoughts welcome!

 
#2
Probably the internal cooling fan, though impossible to say for sure without putting it on a bench. That's the problem with on-line trouble-shooting - it's a mostly ineffective tool that can sometimes make things worse.

I'd still consider buying under three conditions:
  1. If I have a good, thorough & competent amp tech with experience working on SVT's
  2. Price is reflective of the additional cost associated with having the tech diagnose and repair the issue
  3. The amp sounds and performs right otherwise.
 
  • Like
Reactions: Teabag41 and Wasnex
#3
Since it’s louder in the back, it could be the fan. There are many other possibilities.

Some USA made SVT’s had a fixable ground loop hum issue. Before you buy this amp, check out how much it costs to retube it. It’s expensive to replace six power tubes. Only buy if if you have deep pockets.
 
  • Like
Reactions: Teabag41
#4
The video is not very helpful :banghead:.

Observations from the video:
  • I would definitely would want to confirm the sound is not coming from the speaker. The video suggests it is not. Could be the fan, which is a fairly easy fix. Could be something else that is not an easy or cheap fix.
  • Doesn't sound like any malfunctioning fan I have ever heard. Perhaps a noisy power transformer?

I own a bunch of tube amps that I bought previously loved. I would say close to 50% of them needed tubes when I received them. Some of them had blown tubes when they arrived and some had tubes fail within a month or so.

At the very minimum, whenever you buy a previously loved tube amp, I suggest budgeting for a new set of output tubes and a bench fee for a technician to take a quick peak...even if the amp appears to be working properly. Ballpark cost for an SVT is about $500.

Troubleshooting and fixing the weird noise would be additional.

If your lucky the noise is simply a bad fan and the amp work will perfectly for several years once that is fixed. So you are only out $150 or so. Worst case, the tubes are on the way out and the amp has a major problem like a bad power transformer. Repair could easily cost $1200. There is no way to predict which say it will go without actually having a tech go through the amp.

Consider the purchase price and decide if you want to roll the dice.
 
Last edited:
  • Like
Reactions: Teabag41, Pocket Dave and eniac
#6
Thanks for the advice all. I've been back in touch and can confirm it's coming from the head and not through the speakers. The amp plays and seems to sound good, he sent another video confirming that much (potentially another red flag if there's a serious issue going unaddressed while he does that, of course). It's local, so I should be able to go check it out before buying in any case.

Wasnex's post echoes my thoughts for the moment: consider buying at a fair price for a working example, minus about $500. Might get lucky, might still get stung at that price, but hopefully not too badly.

EDIT: I do have a local shop that's done good work for me on a tube guitar amp at a fair price. I don't know the tech personally, he's a contractor, but I do plan on handing any new purchases over to them for a once over.

EDIT 2: I'm thinking I ask if I can point a shotgun mic in the back and see if the noise is coming from any easily identifiable components. Obviously I'm not getting great fidelity from this test, but I'd bet I can tell the difference between a humming transformer at the end of the chassis and a dirty fan in the middle.

I also happen to know the fan is, or was, dirty regardless; I can see a ring of dust on the grill in some of the photos.
 
Last edited:
  • Like
Reactions: Pocket Dave and Wasnex
#9
Wasnex said:
Isn't the fan actually in the front of a CL?
Click to expand...

Yes but the airflow currents pull from the back and make noise. You never know if someone substituted some other fan in there with a higher CFM spec. I sounds mechanical but the buzzing can be many things including from a transformer or a tube.

I really wonder why an amp is being sold with an “unknown” issue. That sends up red flags. My best advice is to avoid it unless a tech identifies the issue.
 
  • Like
Reactions: Wasnex and Teabag41
#12
Pocket Dave said:
A good tech will check fan, transformers, screen/grid resistors, filter caps & bias. A really good one will also tap/visually inspect connections for bad/cold solder joints.
Click to expand...
A good tech will perform a proper diagnostics to determine the source of the problem and correctly identify the cause.
 
  • Like
Reactions: Teabag41 and Pocket Dave
#14
Some auto repair shops offer pre-purchase inspections. For a nominal fee they point out problems (or their symptoms) to the prospective owner, and then the owner decides whether or not to buy the car/truck. I don't know if such a service exists in the amp repair world, but if it does, I'd like to see it become more commonplace. I just don't know how the logistics would work -- potential scams/theft and so on. Maybe I'm dreaming, maybe it's just 2 cups of black coffee kicking in... who knows.
 
  • Like
Reactions: 6thplanet, Teabag41 and agedhorse
#15
eniac said:
Some auto repair shops offer pre-purchase inspections. For a nominal fee they point out problems (or their symptoms) to the prospective owner, and then the owner decides whether or not to buy the car/truck. I don't know if such a service exists in the amp repair world, but if it does, I'd like to see it become more commonplace. I just don't know how the logistics would work -- potential scams/theft and so on. Maybe I'm dreaming, maybe it's just 2 cups of black coffee kicking in... who knows.
Click to expand...

Tech I used to work with before he retired let the seller and I meet in his shop for a couple different purchases, offering to do a quick look under the hood for "about half my hourly bench rate". When I offered to pay, he told me, "don't worry about it - I'll overcharge you the next time you come in."
 
  • Haha
  • Like
Reactions: el_cid, Fishheadjoe, 6thplanet and 2 others

Latest posts

Top Bottom
Back