The V33's first retube

dudesweet157

Senior member
Messages
647
So my V33 has had it stock tubes for over a year now. More than enough time to break in the speakers on my Avatars and plenty of time to form an opinion on the basic tone.

99% of the time, when I plug my Strat straight in, I have the EQ set T: 7.5ish, M: 5, B: 0. This produces quite a good tone at low volumes, but as you crank it up, the bass response becomes overpowering and muddy (even set at 0). It strips away any sparkle and zing, and is quite annoying. Pressing the presence switch brings the attack back, but results in an ice picky tone.

Since I became aware of this phenomenon, I have compensated by dedicating an EQ pedal to tweak the tone into a workable range, but I would like to regain the use of that pedal for other purposes.

I guess my first question is: is this a problem a tube swap can fix? I'm ready and willing to swap out the entire set, but I want to be sure that it will be a change for the better,

My second question is: what tubes would you recommend I use? I need 3 preamp tubes and a quartet of EL84's. I also wouldn't mind if I could get a little less volume. I think if I swap the V1 12AX7 for a 12AU7 it will result in less gain/volume. Is this correct?

Thanks for any and all help. This is my main gigging amp, and it can sound great, it just has too much low end.

-Rose
 

dbw

Senior member
Messages
4,531
12AU7 has less gain than a 12AX7, so you can get less distortion that way.  But the amp will still be loud.   :headbang1:

I have a 5751 which is somewhere in between 12AU7 and 12AX7... it sounds pretty nice.  I know a guy who swears by 5751s over 12AX7s.  SRV also loved them supposedly  :guitaristgif:

Edit: The muddy low end might be from your cab.  Is it an open or closed back?
 

dudesweet157

Senior member
Messages
647
I've got 2 Avatar 212's, both open back.  One with dual Celestion Blues and one with a V30/G12H30 combo.  It exhibits this problem with both cabs, so I don't think it is the cabs that are the problem.  I've also run my Super Champ XD and a Epi VJ through both cabs and it sounds absolutely glorious with either of them parked on top, no muddy low end.  I'm convinced this is a problem inherent to the amp, which led to the question: is this a problem a tube swap can solve?  They're the stock chinese tubes anyway, which should probably have been thrown to the trash heap from day one, but alas I hadn't the money. 

As I said in my previous post, it's quite a nice sounding amp once you tame the low end, it's just the taming of that low end that giving me trouble.

-Rose
 

stratplayer1

Senior member
Messages
298
i have no idea why itd be muddy, im still learning the tube amp ropes, but i've already learned the huge difference new tubes make so go for it, atleast tubes aren't too expensive
 

Patrick from Davis

Senior member
Messages
2,197
While I am not an Amp Designer, there are a number of things that can contribute to this.  The tone stack (set of resistors and caps) are what make the low, mid, and high pots drop off signal for the eq section of the amp.  You can change a couple of components to go from a Marshallesque eq to a Mesa like mid scoop.  It can have a huge difference on the overall sound of the amp.  But you do have to know what you are doing to figure this out, and it would probably void any warranty if ya changed it.

The Tubes will also have a large effect on the sound.  EL34's are too muddy for my tastes, which is why you hear me mention KT77's like a door to door salesman.  The Preamp tubes can have a tight response, and the output tubes can get you gains in definition. 

I still wonder about the tone stack in the amp, why is there that much bass?  When you got the thing, was it designed to have a lot of bass, like that was a selling point?  I sort of was under the impression that the v33's were sort of a Vox sounding amp.  If it still has the original El Cheap-o-rama tubes, a new set will cost a bit and probably sound better.  A good replacement tube to get is a "balanced triodes 12AX7" for the phase inverter.  Generally the cheap tubes are not well balanced and this will dramatically improve the sound.  As far as how the various brands of tubes will sound in that amp, it is hard to say much other than in general terms.  EI's for EL84's seem to have the highest level of karma right now, but they are not the easiest to find.  There was a post 6 months ago where someone had found a source, but I can't seem locate it off hand.  Hard to pin point what to do.  I would say that new tubes will not sound worse, but they might not fix the bass issues.
Patrick

 

mayfly

Senior member
Messages
8,299
You could spend time swapping tubes out, but I personally think that the amp just needs to be voiced better.

The presence switch just adds a feedback loop to the power amp stage, and often uses a cap to select particular frequencies. If it were me, I'd play with the value of this cap, increasing or reducing it and see what effect that has.  This will get you a lot closer faster than tube swapping.  Another thing to try is reducing the value of the bass cap inthe tone stack.  if it uses a classic vox tone stack reducing this to, say, 0.01uf will make a large difference in reducing bass response.  Finally, the cathode bypass cap of the first stage could be adjusted as well.  lowering this cap will reduce bass, and often will have quite a dramatic effect.  Oh one last thing- the caps feeding the phase splitter stage could be reduced, lowering the bass response of the entire amp.

If you are worried about trying this stuff yourself, find a good amp tech in your area and explain to s/he what you are aiming for.  If they are any good, they should be able to tweak it.

That's what I'd do.  Just IMHO.
 
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