How to run an SVT(?)

[Derwin C. Moss (bassdude63)]

I'm hoping someone on this forum can give me some operating pointers on my Ampeg SVT-II Pro head & matching 8-10 cabinet. I've checked everything; The head is switched to 4ohms to match my cabinet,(I've even tried it with another 4ohm cabinet), I'm using a high quality speaker cable and correct gauge of unshielded wire, I've completely retubed the preamp & power sections with matched Svetlana tubes and I still have problems getting adequate volume. Ampeg recommends turning up the preamp gain until the clip led barely flashes, then use the master volume for your overall volume. This method does'nt give good results. A very knowledgeable guitarist has told me to run the master volume at full and use the preamp gain as the overall volume(I'm told this is how the original SVT's were operated). This method is slightly better. I've had the output tested by a tech-he says everything is up to specs. The head has been used on 1 gig, other than that it's had very little use. While it was in the shop being tested I bought a G-K 2000RB that has become my main amp, the Ampeg stack has become my $2000.00 practice amp! Any help would be appreciated. Thanks, D.M.

[Joey Wilson (bigredbass)]

DCM:
Troubleshooting you SVT stack will fall into two categories:
 
1) Switching things around in A/B fashion
. . . and should that fail to find it
 
2) A   Q U A L I F I E D   SVT tech tracking it down on the bench.
 
As for 1):
Your ALEMBIC and your inst cable are obviously not the problem, as the GK has no problems with them.  I'll assume you have the GK and a cabinet for it.  If you're using the Ampeg 8/10 cabinet with the GK, you can eliminate it from the problem list.  Other wise, do this:  
   Play the GK into the Ampeg cab: OK/Not OK
   Play the SVT into the GK cab: OK/Not OK
. . . you can see where I'm going with this:  Keep swapping heads, cabinets, and cables, from the good rig to the questionable rig till you isolate the problem(s).  If after all this,it still comes down to the GK stack works and the SVT stack doesn't, the we'll go to the second option.
 
2) That you changed the tubes yourself entails (among other things) were ALL of them good and of basically the same spec, does the bias need adjusting, did your tech adjust it before or after you did this, etc.  Also, 8/10 cabinets have lots of wire in them for 8 speakers:  Are all the connections good, are all of the speakers good?
 
If the SVT was a new purchase, the reconstituted Ampeg is owned by St. Louis Music, an old and respected wholesaler.  I'm sure Ampeg service can be reached via their website.  Also, be sure your tech knows what he's doing.  Large, multi-tube amps like the SVT, Bass 400+, etc., are not as well understood by everyone these days.
 
By the way, Ampeg is correct:  Adjust the preamp to suit the output of your bass where it's just tickling the clip light, and use your master as your volume.  Running the master wide open all the time will bring up your noise floor, cramp your dynamic range, etc.  This is assuming you want a clean fat sound.  
 
Best Regards,
Joey Wilson

[Joey Wilson (bigredbass)]

DCM:
 
If you're an experienced player, I'm guessing you READ THE INSTRUCTION MANUAL for the SVT and turned up nothing that helps. Don't be like me and read that AFTER I've struck the iceberg . . .
 
Troubleshooting you SVT stack will fall into two categories:
 
1) Switching things around in A/B fashion
   . . . and should that fail to find it,
 
2) A   Q U A L I F I E D   SVT tech tracking it  
         down on the bench.
 
As for 1): Your ALEMBIC and your inst cable are obviously not the problem, as the GK has no problems with them.  I'll assume you have the GK and a cabinet for it.  If you're using the Ampeg 8/10 cabinet with the GK, you can eliminate it from the problem list.  Other wise, do this:
 
   Play the GK into the Ampeg cab: OK/Not OK
   Play the SVT into the GK cab: OK/Not OK
 
. . . you can see where I'm going with this:  Keep swapping heads, cabinets, and cables, from the good rig to the questionable rig till you isolate the problem(s).  If after all this,it still comes down to the GK stack works and the SVT stack doesn't, then we'll go to the second option.
 
2) That you changed the tubes yourself entails (among other things):  Were ALL of them good and of basically the same spec, does the bias need adjusting, did your tech adjust it before or after you did this, etc.  Did you change the preamp tubes as well?  They would certainly affect gain.  Also, 8/10 cabinets have lots of wire in them for 8 speakers:  Are all the connections good, are all of the speakers good?
 
If the SVT was a new purchase, the reconstituted Ampeg is owned by St. Louis Music, an old and respected wholesaler.  I'm sure Ampeg service can be reached via their website.  Also, be sure your tech knows what he's doing.  Large, multi-tube amps like the SVT, Bass 400+, etc., are not as well understood by everyone these days.
 
By the way, Ampeg is correct:  Adjust the preamp to suit the output of your bass where it's just tickling the clip light, and use your master as your volume.  Running the master wide open all the time will bring up your noise floor, cramp your dynamic range, etc.  This is assuming you want a clean fat sound.  
 
Best Regards,
Joey Wilson

[Dino Monoxelos (dean_m)]

Hey Derwin,
 
I hope this helps you out.  I do product clinics for Ampeg amps.  Not that makes me and authority by any means but, I've worked directly with Ampeg on certian things.  On your SVT II, you want to run the master at about 3 o'clock, Just about full up and then adjust your volume with the gain control.  This is how I was told to run my SVT by the guys at Ampeg.  Whatever is going on, it sounds like you have a problem with the head.  Like Joey suggested, play your GK through the cabinet, if you have the same problem, it's obviously something in the cabinet.  If the GK sounds fine, then it's the head.  Also. are you using the 1/4 outs or the speakon connector, not that that should matter but try to isolate if it's a connector problem in the back.  And, are you using the pad switch on the front, if so try turning the pad off.  One more thing, when you replaced the tubes, did you adjust the bias on the back?  On the new style II Pros, they have bias lights right next to the bias controls.  Turn your amp on, let it warm up and take it off standby, be sure its hooked up to a cabinet, you want to turn those bias controls just until the red led comes on and then back them off just until it turns off again.  If it's an older style ProII, without the leds, you need to have the amp biased by an experienced tube amp tech.  One last question, did at any time you ever try to run the amp on without a speaker load hooked up to it?  Doing so with a tube power amp will blow the output of your amp.
I have basically the same rig only I run two 4x10s instead of 1 8x10 and I'm killing anything that comes within 20ft of my rig.  If all else fails, contact Tommy Wilson at Ampeg, he's the Ampeg product manager, tell him I said to have you contact him.  Ampeg is very cool when it comes to taking care of customers.  Email him at twilson@stlouismusic.com.  Tell him what's happening and if he has any suggestions.  Good luck and let me know what happens.
 
Dino

[Derwin C. Moss (bassdude63)]

Joey & Dino, Thanks. Yes, I've already tried all the swapping: G-K through the 810E-OK, SVT through the 4 ohm Goliath Sr-OK(no increase in volume). I've re-biased the tubes when I installed them with the user controls as prescribed in the manual. I use the Speakon connector on the head into the cabinet, but I've also tried the 1/4 output jacks-no difference. I never use the -15db input pad switch, so the problem isn't there. I will e-mail Tommy, thanks for his address. I've contacted SLM numerous times via e-mails and phone calls; I've only been given the most obvious instructions. I'll let you know how things turn out. Thanks again, D.M.