• 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.

Vintage Ampeg SVT noise

vfbsvt

vfbsvt

Oct 6, 2007
4
0
Petaluma, CA
#1
I have a mid seventies SVT that I plug into a 410hlf. The tone is all I want it to be but it has developed a problem that I don't understand. When I'm not playing, I hear a low-level mid-range static-sounding fuzzy crackle sound. The sound disappears when I put the old boy on standby and occurs whether I have my instrument plugged in or not. I have had the amp for a long time and have had the output tubes replaced twice. There is no issue with volume or tone but it is noisy between tunes and that's not cool. Anyone else have similar experience? Any suggestions? I'm on a pretty tight budget and can't afford another overhaul.

Thanks!
 
#2
Hi.

Sounds a lot like the filter caps degrading, and if the caps are original, it's a small wonder that they're still as good as they seem to be.

Using the head regularily and/or powering up with a variac after a longer time of non use are essential in keeping the caps working.

No matter what Your budget is, your description of the problem sounds like a trip to a tech to me.

Regards
Sam
 
#5
I dont recommend changing caps in an SVT unless you know what you are doing around High voltage electronics... the SVT can kill you!!!
I changed mine out myself.. but i have a good knowledge about what is going on and how to do it..
When i was young 25ish i was hit by a discharge SVT cap.. it hit so hard i remember telling myself to breathe.. breathe... in knocked my lights out...
Im 51 now and would not want to take that kind of hit these days.

Id have a tech do it..
 
#7
The line voltage is stepped up to high voltage that the amp can use (transformer). That high voltage AC is rectified to DC for the amps circuits but contains a lot of "noise" from its AC beginnings. The filter caps smooth out and reduce this noise, at the same time provide some DC reserve energy for amp operation.
 
#8
Before you take it in, if you have a spare 12DW7 and 12AX7 laying around, swap them in and out with the ones in it and see if you can locate a bum one. I've had a noise like that happen with preamp tubes as well as with caps. But seeing as how it's a mid-70's SVT that's never had a cap job, it's due for one and you might want to replace them even if it's not the problem. It will probably save you money in the long run. One of those "you can pay me now or pay me later things."
 
#10
6C4's are a very problematic tube, yes. Most are microphonic. Oddly enough, microphonics don't necessarily mean it's gone bad. Mine is microphonic and the amp sounds great. But Ampeg switched to a 12AU7 in its place for a reason.
 

Latest posts

Top Bottom
Back