svt 2 problem

[squish]

i searched for a while on this forum with no luck.

i've got a non-pro svt 2 and it has started a very serious problem. after warming the head for ten or so minutes, i plug in and turn the stand-by off. an audible hum and a *very* weak tone from my bass comes through. then the right bass tone will come in and out for another five minutes and then the problem will finally go away. then, it's beautiful svt tone like i've had for the last six years. i changed the power tubes and one preamp tube that was broken about a year ago. i'm using the same 4 ohm cab. this thing is built so solid and all the tubes light up when it is powered, it has me baffled.

any clue? i've got a show on thursday!

 

[timv]

Try plugging a cord from the send to the return jack.

 

[squish]

as i stated before, this is a non-pro svt 2. so there's no effects loop, if that's what you meant.

help!

 

[brothernewt]

I had a similar problem with the same amp long ago. The input jacks needed resoldering. Had that done and never had another problem with it (other than the weight).

 

[timv]

Sorry, I meant the preamp out to the power amp in. And I have one of these amps so I know it has it.

 

[i_got_a_mohawk]

Could be one of the pre tubes going? seeing only one has been replaced?

As brothernewt said, its probably an input problem

And as timV said, try an instrumental lead from pre amp out to power amp in, ive heard one instance of a problem internally between those connections that wasnt present when you connected them externally

The hum that you mention, does it get louder when you turn the volume up?

(btw, damned good amp!)

 

[squish]

timv recommends that i should patch the preamp out to the power amp in. seems that it is bypassing some circuitry. if that is done and it plays normally, what will it determine?

brothernewt's recommendation is to resolder the input jacks. this seems odd to me since the problem goes away after a few minutes of playing. sounds like you are claiming the heat reestablishes the connection? the hum sound is not affected by jiggling the plug.

yes, the hum increases with the volume.

i love my amp more than any bass gear i've owned...

thanks a lot for the input so far!

 

[i_got_a_mohawk]

if you bypass the internal part that joins the pre and power and it works fine then you know that thats whats wrong

if its increasing with volume its usually not a good thing, take it to a tech, get it the once over, more than likely just a tube going funky

 

[brothernewt]

brothernewt's recommendation is to resolder the input jacks. this seems odd to me since the problem goes away after a few minutes of playing. sounds like you are claiming the heat reestablishes the connection? the hum sound is not affected by jiggling the plug.

yes, the hum increases with the volume.
QUOTE]

I wasn't trying to claim that was the problem and solution... just offering help with what solved a similar problem for me. Mine had the problem very intermittently and frequently more at startup. I don't have a guess as to why.

I had no abnormal hum though, so you may have other problems. I don't have any better input. Take it to a trustworthy tech. Good luck

 

[Jerrold Tiers]

Sure sounds like an opne circuit that is intermittent with heat..... As to where exactly it is, we are all guessing.

The pre out to power amp input jumper makes sense, if the "normaled through" connection inside the jack isn't so good anymore due to corrosion and bar crud. In fact. just plugging a plug into the power amp input usually fixes that temporarily. Contact cleaner is good to use, the Caig Laboratories stuff has a good reputation.

Yes it could be a bad solder connection.

Yes it could be something tube-wise. I'd think about cleaning contacts on all the tube sockets also... that can fix odd problems.

As for us all guessing on the location, you can make some rough but definite determinations....

If you have another amp, and plug the pre-out from SVT into that amp, you can see if it still happens with just the preamp alone (do plug in a speaker to the SVT as a load, please).

Doing the reverse will find it if it is in the power amp and not the preamp.

See which connection still does the drop-out. It is in the part of the unit you are using in that connection.

If it is in neither one, it may have been the jacks, and they have been cleaned by getting used.

 

[squish]

jerrold,

thanks for the advice. last night before the show, i removed all of my tubes (12) and sprayed every leg with deoxIT d5, which i had laying around the house. we had a quick rehearsal before loading out and the amp sounded great!

so as i'm putting the lid back on and bragging to my bandmates about the ampeg guy who gave me advice, the sound started breaking up... just like it had been before. back to square one.

luckily, our multi-instrumentalist is f*ing is rich as hell and just happened to have a spare mesa rig for me to use. talk about weak! it was a buster head and a 6x10. even though it was an excellent backup, it barely cut through on stage with the volume knobs almost all the way up.

guess i'm going to start patching in preamps and power amps to determine what side it screwed up

 

[Luckydog]

i'd say it could easily be bad solder joint that connects when heated. Using same logic, try a different cord. And spray deoxit on input jacks and cord jacks

 

[Tim1]

Had exactly this problem a couple of years ago on the same amp. Turned out to be a dry solder joint in the preamp section, and everything was fine after after a quick dab of a soldering iron.