SVT 3 Pro preamp tube failure

grumpyjfc · #1 01-25-2011, 09:02 AM

As long as I've been screwing around with tube amps, I've never seen a preamp tube fail; until this past saturday. Went through it yesterday & found a bad 12AU7. My gut tells me to change all five tubes but I've read lots of different opinions regarding tube life and/or sound quality. Anyone have any (intelligent) words of wisdom?

JimmyM · #2 01-25-2011, 09:55 AM

how intelligent you think it is is up to you, but no way i'd replace working tubes just because one blew out. it's not like it sets off a chain reaction.

grumpyjfc · #3 01-25-2011, 11:09 AM

Understood, just thought it was odd. Ive had power tubes go out before, but never one of these. Plus, I bought the amp second hand so I have no idea how old the tubes are.

Jimmy M, I've seen you post a lot of replies about amps, do you have an opinion of sound quality between different tube brands?

JimmyM · #4 01-25-2011, 11:20 AM

Quote:

Originally Posted by grumpyjfc

Understood, just thought it was odd. Ive had power tubes go out before, but never one of these. Plus, I bought the amp second hand so I have no idea how old the tubes are.

Jimmy M, I've seen you post a lot of replies about amps, do you have an opinion of sound quality between different tube brands?

not especially, no. to be quite honest, i can't tell a difference between tubes. i did a little tube rolling in my svt recently, and i was very underwhelmed at the difference between the amperex, sylvania, and ge 12dw7's i swapped around.

blackba · #5 01-25-2011, 11:43 AM

12AU7's are not very common tubes for amps, if you look up the number of 12AX7's options and compare them to 12AU7's, you will see what I am saying. My guess, is the current manufacturers of tubes don't much as much focus on 12AU7's.

I would also not replace the other tubes, just replace the bad one. I do have a tube checker though, so I can tell when a preamp tube is getting weak...

Jerrold Tiers · #6 01-25-2011, 09:38 PM

HOW is it bad?

Does it not light up? or is it just weak and crummy?

Did anything odd happen with the FAN when it went bad?

warnergt · #7 01-25-2011, 10:22 PM

Quote:

Originally Posted by JimmyM

...to be quite honest, i can't tell a difference between tubes...

I second that. In my opinion, if the tubes are properly made, there
should be little or no difference. I used to service a lot of tube equipment
back in the 70's (when tubes were still going pretty strong). When I
replaced a tube in a radio (transmitter or receiver), I would always
retune it just in case something changed. More often than not, the
retuning provided no benefit. That is, nothing changed -- even at
radio frequencies.

Then again, these days, tubes are not nearly as consistent as they
used to be. Reliability has gone down the crapper. That's why I
prefer solid state today.

Antipodean · #8 01-26-2011, 01:20 AM

A few months back, my SVP-Pro had a noisy tube somewhere. I didn't know which one it was, but there was noise, crackling, lack of harmonics, and just a general sound of an amp failing. I didn't know which of the 5 tubes (4 12ax7, 1 12au7) was bad, so I just changed all of them.
Sure, it may have been the least cost effective option, but it sounded SO much better after all were changed, that I felt better about changing all of them. But I suspected they were original tubes, and it is one of the black face models (at least 15 years old?)

My theory was that it would cost roughly the same for a tech to check which tube(s) needed changing and replace them as it would to buy a full set.

grumpyjfc · #9 01-26-2011, 08:03 AM

Quote:

Originally Posted by Jerrold Tiers

HOW is it bad?

Does it not light up? or is it just weak and crummy?

Did anything odd happen with the FAN when it went bad?

If i crfanked the volume and the gain all the way up I could just barely make out a faint, incredibly distorted signal. No fan issues. It seems to be working fine now. When I popped the top I fired it up and all the tubes, including the "bad" one were glowing evenly.

Verminaard · #10 01-26-2011, 09:40 AM

It's only $50.00 for a full kit set for the 3 pro on eurotubes. If your 3 pro has the stock tubes and you aren't the original owner then just get a new set. They'll probably be better quality ones than were stock anyways. When I put a new kit in mine the difference was astounding!!

blackba · #11 01-26-2011, 12:49 PM

Quote:

Originally Posted by JimmyM

not especially, no. to be quite honest, i can't tell a difference between tubes. i did a little tube rolling in my svt recently, and i was very underwhelmed at the difference between the amperex, sylvania, and ge 12dw7's i swapped around.

In my SVT3pro I did notice a small difference when switching preamp tube brands, but the originals could have been worn.

With guitar amps I notice a significant difference with tube brands. So I think it just depends on the application and player as to whether the brands make a difference sonically. NOS tubes generally last longer than todays current production tubes, so they are worth some upcharge just for that fact, even if you can't hear a difference. I do think many NOS tubes are priced higher than what they are worth to me....