SVT 4 PRO pre-amp tubes

CurtKemper · Not So Newbie Joined: 14 Nov 2006 Posts: 7

Hi Everyone,

I am new to this forum I read a good bit and there seems to be some very knowledgeable people here so I thought I would ask a question or two.

My Rig:
I have 2 SVT 4 PRO heads that are pushing a pair of 4x10 GK RBH's and a pair of 1x15 GK RBH cabinets. I am front ending these with a line 6 bass pod xt pro, a Dunlop 105Q and a digitech whammy pedal. I switch between 5 different basses and all of them are active. In the effects loop of the 1st head (the one used as a preamp) I put a TC Electronics chorus/flanger. The second head is only used for the power amp section or it gets used if the following happens and I have to switch them. The heads are in cases that I have modified to accommodate the side vent fan on the heads, they are not overheating. The only other thing in the rig is a korg rackmount tuner that plugs into a tuner out on one of the heads.

The problem:
I start to get a swelling sound from the entire rig. Like someone is playing with the master volume turning it up very quickly and then slowly back down. This is an increase in level from where it is normally possibly a 5db gain. This will go on for about 5 minutes and it does not seem to make a difference if it has warmed up or not. Sometimes it does it right away other times it will happen after the rig has been on for an hour or two. Then it stops and everything goes back to normal and I can play through an entire night without issue. Once this starts to happen about 5-6 hours of playing time later the preamp tubes just seem to die. I can't get a clean sound out of it at all and there is no drive or level getting to the power amps. I normally just replace all of the preamp tubes (3 x 12ax7's) and the problem goes away for about a month. I have pulled everything off the front end to make sure it was not one of the effects causing it.

What should I expect the lifespan to be on a set of preamp tubes (in hours) with these heads? I have been using groove tubes with a rating of 8 or greater.

Is there a better way to hook all of this up?

I am not running these heads at a high output or level. They are split to either side of the stage mainly as monitors for the guitar player and myself but I do take the load off the PA in smaller venues that don't have the bottom end in the PA. He is doing the same thing with a pair of Marshall half stacks.

Thanks in advance,
CK

bigdirtyk · Posted: Fri Nov 16, 2007 12:34 am Post subject:

The amp that is going to your speakers, are you running stereo or mono? I was having some problems with my svt=4 and my two ampeg 8x10's. after messing around with it I realized there was a small button you need to push when to switch between stereo and mono. It took care of the volume problem that I experienced

CurtKemper · Not So Newbie Joined: 14 Nov 2006 Posts: 7

I am running my rig mono. After a bit of frustration with this I found out that it was being caused by the input power fluctuating. It was a difference of 112 volts dropping to 108 volts AC. It was enough to cause the amp to change the output levels. There was a construction site that was on the same power grid my house is on and they were drawing a lot of power. When they were not working it stopped. I am not sure what they were using, welders or some other high power device but the problem has corrected itself. I have been looking into some sort of power conditioner or regulator that will eliminate this altogether but all of them that I have looked at are really big and heavier than I want to haul around at this point.

Curt

bigdirtyk · Posted: Fri Nov 16, 2007 10:05 am Post subject:

I've been wondering about the significance of a power conditioner. I always thought they were just a glorified surge protector. Do you think they are a necessity in a rig?

CurtKemper · Not So Newbie Joined: 14 Nov 2006 Posts: 7

bigdirtyk · Posted: Sun Nov 18, 2007 7:31 pm Post subject:

Thats a kicka *Horse's Patoot* idea! I don't know why the hell they put the vents on the side?!?! I'm going to drill a decent size hole in the side of mine now though, I appreciate the advice!