AMPEG SVT 2 PRO PROBLEMS! AGAIN! UGH.

punkrockmike · #1 09-24-2011, 09:04 PM

So after taking my 2 pro into the tech and having the tubes replaced and some circuitry fixed, everything was working fine for about a week. Apparently the problem was that a bad tube or two had damaged something else inside the amp. now, after only a week of having it back, the right bias light is telling me i have a bad tube. everything sounds fine, but that light makes me nervous. is it normal for the bias lights to change occasionally when i bring the amp from location to location? we just moved all our gear into a practice space. and also, will overdrive pedals kill tubes or cause other problems with my amp? im currently using a odb3 and a sansamp bass driver. please help! im so frustrated.

JimmyM · #2 09-24-2011, 09:23 PM

If the amp sounds fine, chances are it is, but you can't rule out the possibility of a new tube going bad on you. First, have you tried to rebias it yourself and still got the same result? If so, since they're new tubes, you should be covered under warranty if it's only been a week. So I'd call your tech on Monday and let him know what's doing.

**B-string** · #3 09-25-2011, 12:19 AM

As a tech I didn't put great faith in the user bias gimmick, but if the LEDs were both green something may have drifted with one new tube. Output tube warranties vary per vendor but I have not seen less than 30 days so get it back now for a check out. NP (New Production) tubes do have a higher failure rate than the "old days".

punkrockmike · #4 09-25-2011, 01:15 AM

alright ill try rebiasing it tomorrow after work and get back to you. so you dont think the overdrive pedals have anything to do with it?

johnk_10 · #5 09-25-2011, 01:45 AM

Quote:

Originally Posted by punkrockmike

alright ill try rebiasing it tomorrow after work and get back to you. so you dont think the overdrive pedals have anything to do with it?

IMO, it's definitely not the pedals.
my guess is that the new tubes have now 'settled in' and they've drifted from their initial bias setting. when resetting the bias, it can take up to 15-20 minutes of the amp being on to get the tubes at their normal operating temp.

punkrockmike · #6 09-25-2011, 02:18 AM

alright so should i just leave it on standby for 15-20 minutes before i bias it?

throbgod13 · #7 09-25-2011, 03:00 AM

read the owner's manual, first.. then take it back to your tech..

Bassmec · #8 09-25-2011, 04:20 AM

Quote:

Originally Posted by punkrockmike

alright so should i just leave it on standby for 15-20 minutes before i bias it?

No you should leave it on, not in standby mode but with the high tension connected to the tubes.
This drifting of quiecent current in some new production tubes is very annoying, you buy a nice matched set and two months later thats not what you have anymore.
I have resorted to buying cryogenically treated winged C tubes in the vague hope that some of my re-biasing and repair work will remain adjusted properly for more than a week.
Its a bit depressing that to semi permanently cure your problem is really going to cost circa $930 these days for a set of tubes made in a factory with some form of quality control
rather than just use the customer to filter their stock.
Power output vacuum audio tubes

Jerrold Tiers · #9 09-25-2011, 08:23 AM

Does sound like drift, although other things are a possibility.

OD pedals won't kill things, as a rule, but they MAY cause tubes to "settle in" faster.... Just a function of working the tubes a little harder.

The good news is that you really only need to match them in sets of 3, which means it is possible that some shuffling will find two groupings that each are close enough to work without the ^%$#! lights complaining at you. (even if the groups are not exactly matched to each other).

I doubt that the tube makers do much burn-in any more..... and at least one other poster seems to have gotten tubes that were never 'flashed off" to the proper high voltage to reduce arcing.

Probably the people making tubes these days were not even born yet when tubes were in mass production. They don't know what they can cut out of the process and what they cannot. Or maybe they found that people will buy them anyway............ QC or no QC.

punkrockmike · #10 09-26-2011, 01:09 AM

so i rebiased it and it seems to be back to normal. still gonna call the tech tomorrow. any other suggestions?

JimmyM · #11 09-26-2011, 01:14 AM

Ya, give it a few days before you call your tech. All he'll say now is, "Well, call me back if it drifts again."

Muziekschuur · #12 09-26-2011, 01:17 AM

Punkrockmike CONGRATS MAN..... You fixed it....
Now get drunk and enjoy..... (oh.... f.... its monday...)

johnk_10 · #13 09-26-2011, 01:19 AM

Quote:

Originally Posted by punkrockmike

so i rebiased it and it seems to be back to normal. still gonna call the tech tomorrow. any other suggestions?

i'm sure that it's fine now. take Jimmy's advice, i.e. there's no need for the tech to see it unless it keeps drifting. it's also possible that the tech didn't wait a full 20 minutes when he set it in the first place.

tech21nyc · #14 09-27-2011, 10:44 AM

Quote:

Originally Posted by punkrockmike

So after taking my 2 pro into the tech and having the tubes replaced and some circuitry fixed, everything was working fine for about a week. Apparently the problem was that a bad tube or two had damaged something else inside the amp. now, after only a week of having it back, the right bias light is telling me i have a bad tube. everything sounds fine, but that light makes me nervous. is it normal for the bias lights to change occasionally when i bring the amp from location to location? we just moved all our gear into a practice space. and also, will overdrive pedals kill tubes or cause other problems with my amp? im currently using a odb3 and a sansamp bass driver. please help! im so frustrated.

Overdrive pedals won't kill tubes but if you are boosting your signal a great deal this will cause the output stage to work harder. The harder you run the amp the less mileage you will get out of a set of output tubes. Also depending upon the way you are using the BDDI you may want to engage the input pad on the amp so as not to create unwanted preamp distortion.

punkrockmike · #15 11-28-2011, 12:52 AM

Quote:

Originally Posted by Muziekschuur

Punkrockmike CONGRATS MAN..... You fixed it....
Now get drunk and enjoy..... (oh.... f.... its monday...)

Yea you're right. i can only start drinking on mondays if its before 9am. otherwise i black out and pass out too late and it messes with my sleep schedule