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SVT CL no sound/buzz only

doomloop

doomloop

Mar 1, 2011
118
0
Portland, OR
disenchanter.com
#1
So some of you probably know some of my story already....replaced all my tubes in my SVT, brought it to a tech for piece of mind but everything was good. I played two gigs and practices and everything was great...

I let my amp sit and cool for about 90 min after a gig loaded it in my van and left it overnight...it was a pretty cold night, maybe 30, but it was covered and the van is pretty well insulated. Brought it in the next day, took it to practice, warmed it up and BUZZZZZ.... :mad: :bawl:

That's it, lights are green, no changes/sound from playing bass, when I dial the bias lights to red the buzz increases but that's about it, as it would under normal circumstances when there is sound...no output other than that.

Tried cables, bass and cabinet...

Thanks for the help!
 
#2
Sorry to hear the bad luck and dont have much to offer in a diagnosis. The svt cl heads are pretty stout but I always have carried mine in an ata road case and have always brought it inside after a gig. The roadcase insulates it from rain, snow and extreme temp changes, but even after a long gig I drag all electronics back into my house. I used one on the road and it banged around in the back of a truck in all sorts of temp changes without any issues. I'd be surprised if the cold or vibration actually caused the problem. It might have aggravated an existing problem though.
 
#4
First thing, plug your bass into the power amp in jack on the back and see if you get any sound out of it.

The CL has a number of connectors inside the amp. The cold may have shrunk one loose enough to loosen a contact. Reseating the internal cables might help. While you got it open do the same to the pre-amp tubes.
 
#5
Same thing happened to my SVT-VR, exact same thing, used it, everything was fine, got home late, left it in my truck, cold night, etc.........
Next time I tried to use it...........nothing.

Turns out the cold had nothing to do with it, for whatever reason the thing would not come out of "protection mode"

Luckily I live in Washington and Hodgy took care of everything!!!!!!!
 
#10
I've been inside this amp before and am aware of the dangers, that being said I tend to only swap tubes. I can deal with a Laney AOR but the SVT is a pain to navigate.

All the tubes in the back seem fine, they all glow appropriately and when I hit the stand-by to on they get just a little blue in them in a uniform manner and on all of them...I was considering perhaps the front pre-amps tubes could be an issue just because they are not normally visible and the others seem fine.

I have a full set of pre's I can swap...would a misaligned power tube cause this symptom and if so would it glow differently, or at all, if in fact misaligned in a socket?

Thanks again everyone.
 
#12
Cold shrinks things.... probably some connection or component opened up.

A tech would trace the circuit through the unit, checking to see where the signal stops. the problem will be there.

Checking if you get music out when playing with cord plugged into power amp input will determine if the problem is in preamp or power amp.

It might even fix the problem, if it is a matter of corrosion on the jacks.... Plug into every jack on the thing a few times (power off, please) and try again. if no joy, take to tech.
 
#13
Sad to hear. My Heritage SVT-CL has been mysteriously going to fault mode from time to time during gigs. So far no rhyme nor reason for it I can figure out. Told Hodgy about it and he thought it might be a bad power tube but they all bias just fine. I'm still using it since 99% of the time it's fine, but it's frustrating when it happens. I have to quick power off and on again. Everything is fine after that for the rest of the night. Weird.
 
#14
Mastermold said:
My Heritage SVT-CL has been mysteriously going to fault mode from time to time during gigs.
Click to expand...


If there is a problem with a power tube it can be intermittent. This could happen with temperature or vibration. So the amp might indicate that the bias is fine and then something causes the tube to fault out while playing.

It is important to remember that the line voltage affects the bias and other voltages in the amp. If the wiring at the venue is not up to standards and the line voltage load gets too high when all the equipment is being pushed, the line voltage will sag causing the amp to fault. The only way to know is to monitor the AC line voltage with a data logger while you are playing. Not easy to do without specialized test equipment.

So the "simplest" fix would be to inspect the tube sockets, their tension, and try a new set of tubes and see how it goes.
 
#15
Mastermold said:
Sad to hear. My Heritage SVT-CL has been mysteriously going to fault mode from time to time during gigs. So far no rhyme nor reason for it I can figure out. Told Hodgy about it and he thought it might be a bad power tube but they all bias just fine. I'm still using it since 99% of the time it's fine, but it's frustrating when it happens. I have to quick power off and on again. Everything is fine after that for the rest of the night. Weird.
Click to expand...

This was also happening to mine at a few different venues. So after a lot of investigating and two or three techs looking everything over and coming up empty handed. I found out that my CL and SVT VRI's do not have the same standby mode as the older ones. At particular places if mine was getting voltage that dropped below 118 (if I remember correctly) it would go to standby mode(red light) and be done for the night. So I had a easy mod done to my standby and it's been fine ever since. I've got the schematics and procedure somewhere I could dig it up and send it to you if you need it. I do not know if the heritage is the same. I thought they were built like the old ones with a manual standby? Maybe Jimmy will come to the rescue and help you guys out.

As far as Doomloop's problem I think this is not it. Maybe though who knows?
 
#16
10cc, that sounds like a different problem than what's happening with doomloop. But as far as I know, it's only a problem with the VR, and 113v is the magic number.

http://johnkvintageguitars.homestead.com/SVT-VR.html

This details a fix you can do for it. Hodgy says there's also a fix for it that's different, but I don't know about it. Again, though, I don't know if this will help Mastermold and I doubt this is the problem doomloop is having.
 
#17
I'm guessing that going into protect would be indicated by the flashing red and green lights on the front of the amp?
Mine is not doing this so I will try visually inspecting some connections, probably won't dig around too much for the obvious reasons, and re-seat my tubes, swap some pre's and try all the jacks as suggested. After that I'm just gonna bring it in again.

Thanks all! If anyone thinks of something feel free to lemme know!

btw...here's some of my bands music when my amp IS working fine...lol

http://disenchanter.bandcamp.com/
 
#18
beans-on-toast said:
If there is a problem with a power tube it can be intermittent. This could happen with temperature or vibration. So the amp might indicate that the bias is fine and then something causes the tube to fault out while playing.

It is important to remember that the line voltage affects the bias and other voltages in the amp. If the wiring at the venue is not up to standards and the line voltage load gets too high when all the equipment is being pushed, the line voltage will sag causing the amp to fault. The only way to know is to monitor the AC line voltage with a data logger while you are playing. Not easy to do without specialized test equipment.

So the "simplest" fix would be to inspect the tube sockets, their tension, and try a new set of tubes and see how it goes.
Click to expand...

Thanks for this, I think I am going to take to a tech for a peek and may end up with some new tubes. If it happened every gig I'd be all over it but because it's so hit and miss it's easy to ignore and play on. For now at least.
 
#19
Mastermold said:
Thanks for this, I think I am going to take to a tech for a peek and may end up with some new tubes. If it happened every gig I'd be all over it but because it's so hit and miss it's easy to ignore and play on. For now at least.
Click to expand...

Here is an old tech trick for your amp tech to find marginal tubes. While the tubes are in a "tube tester" (marginally useful piece of equipment IMO) with the tube fully warmed up and displaying GM or emissions drop the heater voltage one step down. "Good" tubes will display no or very slight loss, weak or questionable/bad tubes will have a notable loss. We used to call this a "life test". My MU-401 has a switch named that, it's major function is heater voltage drop. If you run into low supply voltage or line "sag" this test is useful also.
 
#20
JimmyM said:
10cc, that sounds like a different problem than what's happening with doomloop. But as far as I know, it's only a problem with the VR, and 113v is the magic number.

http://johnkvintageguitars.homestead.com/SVT-VR.html

This details a fix you can do for it. Hodgy says there's also a fix for it that's different, but I don't know about it. Again, though, I don't know if this will help Mastermold and I doubt this is the problem doomloop is having.
Click to expand...

Yep, maybe not and yep. Maybe not because mine is a CL and it must have been you that posted that link before if so THANK YOU! Since then and since the mod mine has been running great!

Again sorry doomloop for loosing focus. Hope you get your amp fixed. Hit us up with a follow up after your problem has been found and fixed. I always try and catch up on SVT news because troubleshooting sucks if your looking in the wrong direction.
 

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