SVT Experts

[Nighttrain1127]

I have a 71 Blue line that has not seen much action in the past two months (like none) . So I was using it for rehersal Friday night and it starts this thing where it kind of screeches But almost like an electronic buzz kind of thing. Then it does this tic,tic,tic thing then Buzzes again and quet for a minute or two then does it again . It did this for about 5 minutes then stopped and worked fine after that all night . Any Ideas what this might have been ?

 

[Floyd Eye]

Sounds suspiciously like the fan to me.

 

[anderbass]

Did you try the other input channel to hear if it buzzed too?

 

[themacinator]

Sounds like a job for JimmyM and Beans-On-Toast to me.

 

[BassmanPaul]

Is the noise coming through the speakers or emanating from the amp itself?

 

[JimmyM]

Sounds like a job for JimmyM and Beans-On-Toast to me.

More Beans than me. All I can tell you is there's something wrong and you should take it to a tech.

 

[Floyd Eye]

B string knows some **** too.

 

[jarrod cunningham]

Sounds like a preamp tube .

 

[SactoBass]

I have a 71 Blue line that has not seen much action in the past two months (like none) . So I was using it for rehersal Friday night and it starts this thing where it kind of screeches But almost like an electronic buzz kind of thing. Then it does this tic,tic,tic thing then Buzzes again and quet for a minute or two then does it again . It did this for about 5 minutes then stopped and worked fine after that all night . Any Ideas what this might have been ?

It sounds like one of two things to me:

1) a tube problem.

-OR-

2) send/return jacks are dirty (if your amp has them). This is what happened to my '91 SVT-II non-pro. As soon as I plugged in a patch cord from the send to the return, the problem stopped. My amp tech told me that this problem can happen due to the jacks getting dirty. He replaced the jacks, and bingo, the problem went away. I do not know if '71 SVTs have send/return jacks.

 

[B-string]

Has the unit been cleaned out or does it have a lot of dust built up? Dust with a little bit of moisture is conductive in the presence of high voltage (heat will dry it out after 5 minutes or so). Have all the electrolytic cabs been replaced in the last 20 years?

 

[beans-on-toast]

I'll add…

I'd blow out the gunk, then look at the tubes if the sound was coming from the speakers. Start with the pre-amp tubes. A tech might start by applying deoxit and reseating the tubes.

Tic, tic, tic can come from thermal expansion of the metal structure inside a tube as it heats up. Not a good sign. Buzzing could be an intermittent connection. A short at the tube socket is another possibility. Look for black soot around the tube socket. As was mentioned, dust in the fan can make a mechanical noise like you described. So you have to try to determine if the source of the problem is electrical or mechanical.

When it is working properly, is there a background hum that is louder than normal? This goes with what Jon was asking about the age of the caps.

 

[Nighttrain1127]

Sorry It has taken me so long to get back (death in Family). I cleaned out all the Gunk Before I turned it on . The Fan runs smoothly And spins freely No Bearing bind or roughness. I checked the tubes and sockets no Signs of arcing That I can see. The noise is coming through the speakers. I tried both Channels and it makes the same noise even with no Input . I had a new set of pre tubes but did not install them because the noise has not come back and there is no hum that is louder than normal. I Believe the caps have been replaced. The noise almost sounded like a relay opening and closing with the buzz possibly being an arcing sound. I do Know the very basics of electronics but anything besides replacing tubes and minor cleaning is out of my safety Zone

Thank you for all your assistance so far

 

[JimmyM]

You probably fixed it.

 

[okcrum]

If your power is dirty it might just be that. My SVT made some scary sounds when it got inadvertently put on a circuit with two fryers and a couple of cash registers. A good power line filter would cure that.

 

[nysbob]

You might also try "exercising" your rockers. I've had some weird sounds come out of mine when they aren't positioned solidly.

 

[Nighttrain1127]

No rockers on Blueline but the switches were moved a few times on and off when the noise started.
Update Used the amp for about 4 hours yesterday with no Issues.

 

[rickdog]

... it starts this thing where it kind of screeches But almost like an electronic buzz kind of thing. Then it does this tic,tic,tic thing then Buzzes again and quet for a minute or two then does it again.... Any Ideas what this might have been ?

You didn't have a cell phone near the amp or your bass, did you?

 

[okcrum]

You didn't have a cell phone near the amp or your bass, did you?

We just might have a winner.

 

[nysbob]

No rockers on Blueline but the switches were moved a few times on and off when the noise started.

ALL tube SVTs have rockers.

 

[christw]

You didn't have a cell phone near the amp or your bass, did you?

Every AT&T phone I ever had talked loud through amps. My old bands used to give me a dirty look whenever my phone was communicating with the network. I ended up having to turn it off for most practices and gigs because of the issue.

ALL tube SVTs have rockers.

Found this in another thread. It's bean's '71 SVT. See the switches?