bad 80's svt distortion. help!

punkrockmike · #1 11-27-2011, 11:15 PM

just picked up an mti era svt. sounded amazing when i was playing through it at the guy's house before i took it home. got to the practice space, plugged in, let her warm up on standby for a bit, then my jaw dropped as i played a couple notes. it sounded like a crappy fuzz box. it also sounded way too full and loud (i only had the volume turned up to three) and there didnt seem to get much louder from three to five. im going to bring it to the tech as soon as i have a chance this week but i was wondering if anybody had any idea what this could be before i bring it in. i tried different instrument cables, speaker cables, speaker cabs, and a different bass. the sound was still there. is there a possibility something got knocked loose on the way home? what should i look for?

punkrockmike · #2 11-27-2011, 11:17 PM

also forgot to mention that it would sometimes sound really thin too. so it fades from really full to really thin, and sounds like a cheap fuzz box is being run into it.

punkrockmike · #3 11-27-2011, 11:25 PM

and it even happens when i turn the volume waaaay down.

punkrockmike · #4 11-27-2011, 11:28 PM

the power tubes are newer but the preamp tubes are original. all the power tubes look good when its fired up, but the preamp tubes look a bit strange. some of them look pretty old and dirty (obviously) and some of them are a bit brighter than others. also, when i was moving it from the van to the space, it almost felt like something may have been loose in there.

T-Bird · #5 11-27-2011, 11:29 PM

Hi.

Keeping the electrical safety and common sense in mind, You can wiggle the tubes in their bases, use your cables plug to "clean" any and all the jacks.

Edit: With the amp UNPLUGGED from the mains, obviously.

Regards
Sam

punkrockmike · #6 11-27-2011, 11:32 PM

thanks man ill give that a shot. the thing was sitting in the same room in this guy's house for about three years. he said he would fire it up about once a month and jam for a bit but three years of very minor use may have allowed things to get kinda dirty.

oinkbanana · #7 11-27-2011, 11:33 PM

start by checking that the tubes are all seated.

punkrockmike · #8 11-28-2011, 12:02 AM

oh and also there is a bit of a crunch around 1 and 2 when i turn the volume knob, but i assume thats just a dirty pot?

anderbass · #9 11-28-2011, 07:05 AM

Do you get the same problems when trying each of the input channels?

beans-on-toast · #10 11-28-2011, 08:51 AM

It sounds like something got knocked loose on the way home as you said.

The problem could be due to anything such as a loose tube, a bad solder joint, or broken component inside the amp. As others have suggested, the easiest thing to try is to wiggle all the tubes and make sure that they are well seated. There is also a bundled cable that runs from the preamp to the power amp. Reseat this, making sure that it is pushed all the way in. Do this carefully.

In any event, you should have a tech inspect the amp and clean all the contacts and pots with DeOxit. If necessary, install a three-conductor power cord and replace the power supply caps. Whatever the problem is, they'll sort it out.

All amps need some maintenance, especially ones that have sat mostly unused for long periods of time. It comes with buying a used amp. This will provide years of service and is well worth the investment.

SOB H.R.MC · #11 11-28-2011, 12:13 PM

I had a similar problem and it was the output jack on my bass (Charvel 3B with active eq/preamp)
ps I assume you are using 4 ohm cabs

Bassmec · #12 11-28-2011, 12:56 PM

Quote:

Originally Posted by punkrockmike

oh and also there is a bit of a crunch around 1 and 2 when i turn the volume knob, but i assume thats just a dirty pot?

You might have a failing pre amp tube or dirty connexion for the heater circuit in one tube socket, if you are describing the bass
coming and going.
A decent tech should fix this in no time, clean the pots, sockets and switches, then reset the bias.
The output impedance load is 4 ohms a cab don't mess about with bad speaker cables or unknown cab impedances and it will
be very reliable.

punkrockmike · #13 11-28-2011, 04:36 PM

thanks a lot for the advice guys. running it into a good ol ampeg 810e (tried it through an ampeg 610 as well. all 4 ohms as you all know). tried multiple basses too (recently replaced the jack and pots on my bass so i already figured it wasnt that, but tried another one just to be sure). ill try wiggling the tubes a little and see if that helps. ill be dropping it off to a tech later this week so i guess i could just leave it alone til it gets looked at. thanks again guys!

punkrockmike · #14 11-28-2011, 04:38 PM

and yes, anderbass. all inputs.