Ampeg SVT owners please come in.

thedudebrah · #1 02-19-2013, 03:51 PM

Where does your SVT start to break up?

I have the SVT-VR and I'm hearing some distortion with the volume knob on 9:00. All other controls are set flat, no rockers engaged. I've had this in the shop for the past month and the tech swears up and down that nothing is wrong with it and its pushing 350 watts, which sounded odd to me.

Also, there is a constant buzz coming from the amp, similar to an unshielded bass, but it does it all the time. This gets worse if I use the ultra hi rocker.

The amp is 14 months old and I used to be able to push this thing with both channel volumes close to 11:00 before I got any break up. It should be mentioned that I never use tube distortion in my sound, so this is a negative for me.

Is this just a bad tech? I don't know how he could plug a bass in and not hear any distortion. It hasn't sounded right to me since he fixed the original problem that I had.

This is the original repair ticket. Before I take it somewhere else, I want to get the opinions of some fellow SVT owners.

zachoff · #2 02-19-2013, 04:05 PM

Mine's ('76) pretty clean up to 12:00 or so. Might start to break up at 11 if I really dig in and I'm playing my L-2000. Other, lower output basses don't start until about noon & even then it's just a bit of grit and not all out breakup.

Might be you have early break tubes in there? If not, I'd get a 2nd opinion.

**mjac28** · #3 02-19-2013, 04:09 PM

If it still isn't performing like it used to and buzzing I would get a second opinion. I play at low volumes and when I had my SVT I never pushed it I was afraid of that amp

thedudebrah · #4 02-19-2013, 04:17 PM

Here's a video of it. iPhone camera isn't the best to record with, but you can still hear the buzzing. Volume wise, I go 9:00, 12:00, and then dime it. Bass knob completely down, rockers flat. MIM 50s P with both controls maxed. I get the same results with every other bass I own.

http://i15.photobucket.com/albums/a3...B4C40217F9.mp4

I know my playing is garbage btw.

GBassNorth · #5 02-19-2013, 04:20 PM

My SVT-VR stays dead clean up to noon with my passive basses. I can get a little breakup just before that with a really hot feed like one of my Spectors or a G&L 2500.
The only noise I get thru mine is the typical hiss on channel 2. I just turn the volume down or off on 2 and it goes away.
I'd say get a second opinion.

Jazzbass2010 · #6 02-19-2013, 04:31 PM

I play 62 ri jazz bass through svt vr . I can get to around 10 o clock or so i wont say it distorts it just comes in to its own . A beast to haul then i plug in to it worth it every time . At 12 i cant hear guitar player or keyboard player any more . I find the 62 ri has low out pickups . Other wise it sounds amazing . Anxiously awaiting for p bass

JimmyM · #7 02-19-2013, 06:47 PM

Might have a pre tube that works but is weak. That happened to me in my B-15.

And totally try a new tech.

JOE EDO · #8 02-19-2013, 06:55 PM

Start with the cheapest components first..pre tubes. If that dosen't do it you may have one with the dreaded ground loop issue. Check this:
http://music-electronics-forum.com/t15670/

I also agree with Jimmy..get a new tech! One that has at least better handwritting. Once you get the bugs out, you will find the VR a fantastic amp that will deliver everything you are looking for.

thedudebrah · #9 02-19-2013, 06:56 PM

Thanks for all the suggestions guys. The tubes that are in it are all stock, as I bought it new just last year. The issue I posted earlier in the thread is the first problem I've had with this amp. That repair tag also makes no indication of replacing any tubes Jimmy, so that might be a possibility. Luckily there's a great tube amp repairman near me that I'll be talking with later this week. I'll bump this thread with updates. I tried it out tonight at band practice an it just didn't sound or feel the same.

nysbob · #10 02-19-2013, 08:21 PM

Through my single 15" cabs, my magnavox SVT starts to get a little distorted around 11 o'clock - but at that point it's so stupidly loud I can't really be sure if my speakers or my ears are distorting.

I usually run it between 10 & 10:30 with all rockers off, mids centered at 800.

B-string · #11 02-19-2013, 08:42 PM

I have seen you post that repair ticket before.

thedudebrah · #12 02-19-2013, 09:32 PM

Quote:

Originally Posted by B-string

I have seen you post that repair ticket before.

Yeah like two months ago...and I'm still unhappy and don't feel that it has been repaired correctly. The guy claims that he can't find a problem, but I'm hearing distortion before I'm hearing volume, and that ultra hi switch never hummed like that before.

I have a gig this Friday and I plan on using it, just so I can hear it using a different power supply in a different acoustical setting. If the problem persists, it's going to a different tech.

Old Fart · #13 02-19-2013, 09:41 PM

When you need a doctor or a lawyer or an amp tech, don't bargain shop. Find out who is the best and take your business there.

beans-on-toast · #14 02-19-2013, 10:12 PM

There are a lot of possibilities.

The first thing that I would check is the small 12AU7 tubes in the power amp. If there isn't enough drive, the amp will distort like that.

Make sure that the 12AX7 and 12AU7 tubes are in their correct sockets. It can happen. You don't want them in the wrong place.

Plug an instrument cable into the pre-amp out and plug into another amp. If you can't plug into a power amp, plug into the input, just watch your volume levels. Chaining two pre-amps can result in a lot of distortion. See if the other amp distorts in the same way. This will help you determine if the problem is in the pre or power amp.

thedudebrah · #15 02-19-2013, 10:33 PM

Quote:

Originally Posted by beans-on-toast

There are a lot of possibilities.

The first thing that I would check is the small 12AU7 tubes in the power amp. If there isn't enough drive, the amp will distort like that. Make sure that the correct tubes are in the correct sockets. It can happen.

Plug an instrument cable into the pre-amp out and plug into another amp. If you can't plug into a power amp, plug into the input, just watch your volume levels. Chaining two pre-amps can result in a lot of distortion. See if the other amp distorts in the same way. This will help you determine if the problem is in the pre or power amp.

Interesting. I'll try that tomorrow with my Acoustic head. How should I connect to the cab? I don't want to run the tube head without a speaker load.

beans-on-toast · #16 02-19-2013, 10:37 PM

Yes, you need to have the SVT cab or a dummy load connected when the amp is powered up, otherwise you can damage the amp. Just don't listen to it when performing the test.

A tech would use a dummy load and perform the test without the cab connected. Most folks don't have one laying around.

nysbob · #17 02-19-2013, 10:42 PM

I never have been derive any benefit from chaining the channels (it ain't a marshall) and the top boost switch doesn't yield anything I find pleasant...so I don't do anything overly dramatic with the front end in deference to it being a nearly 40 year old amp...just go in #1 normal and it bestows the tonez.

B-string · #18 02-20-2013, 09:45 AM

Quote:

Originally Posted by thedudebrah

Yeah like two months ago...and I'm still unhappy and don't feel that it has been repaired correctly. The guy claims that he can't find a problem, but I'm hearing distortion before I'm hearing volume, and that ultra hi switch never hummed like that before.

I have a gig this Friday and I plan on using it, just so I can hear it using a different power supply in a different acoustical setting. If the problem persists, it's going to a different tech.

Thought so. I was not impressed by the repair ticket. You should find a new tech and provide them a copy of the repair ticket. This guy might have done something wrong with the bias circuit. Improper bias or balance could be causing the distortion and early breakup. I just have little faith repairs were done properly and now they seem to be incapable of finding the error in the work performed. IMO from the description of what you have provided (not there to see and/or hear the unit).

The 60 Hz buzz in the preamp could be a faulty tube but sounds like a ground that was left loose or improper routing in re-assembly.

Steve Dallman · #19 02-20-2013, 10:00 AM

I still think you are not getting output from one side of the power amp. Your description sounds like the amp is "single ending" by running only through the tubes on one side, which would cause single ended noise, low output and distortion. You need a different tech. The one who did the work isn't up to working on an SVT.

thedudebrah · #20 02-20-2013, 11:48 AM

Is there anything I can do to check the bias myself with no tools, or should I leave it to the tech? Both side bias lights illuminate as well as the balance light when the amp is under load. I can also see that all the pre and power tubes are illuminated, that's as far as my knowledge goes on that lol.