Tube Upgrade?

J

jonny deep

Disappointing Member
So, my little Vox Night Train 15W head (the NT15H) has a problem - at medium gain settings it produces a kind of fizzy rattly noise at the start of each note played, that settles after about a second or so. I took it into the shop and we determined it was indeed the amp and not my guitars (I could play other amps without the issue).

The man in the shop told me that this is common in low power amps when you start to push the tubes. I've researched online and found others with the same issue - some say it can be fixed with new preamp tubes; others say that it's to be expected in mass produced, low cost amps like this (i.e. they're very hit and miss) and can't be solved.

So, I've decided to try a tube swap before I give up on the amp. My online research suggests that a JJ ECC83s 12AX7 tube in slot 1 and an EH 12AX7 tube in slot 2 is the best combination.

Any thoughts/comments? Am I wasting my time? Any better tube combos I should consider?

Many thanks in advance! :D

Edit - Do I need to consider matching or biasing? I believe the Night Train doesn't require re-biasing, but not sure if I need to consider the bias of the tubes in conjunction (note - I am a total noob at tube amps).
 
Don't worry too much about preamp tube brands and where to put them. You most likely will not hear much of a difference, and if you do, it will be pretty minimal. Of all the things that can alter guitar tone, tube rolling is about 77th on the list. It's fun to try and it's good to have extra tubes on hand, but it really is a tiny difference, if any. Good quality tubes will be better than cheap stock china tubes, but with good tube vs good tube you won't hear much difference.

Having said that, I like Electro Harmonix and Tung-Sol better than JJ's in my own amp. JJ's have a rep to be a little "darker", and I find that to be true myself. Tung-Sols and EH are cleaner sounding to me.

You don't need to worry about biasing with preamp tubes.
 
Hey Greg - thanks for the response.

I'm happy with the tone of the amp overall - it's just the scratchy, fizzy, rattly sound at the start of each note played that just doesn't record well (or sound great at all). It's not a smooth breakup tone that I'd expect and I have read it can be because of the low quality stock tubes (they're Sovtek, apparently). Maybe this all just means that I don't like the amp's tone, as it is a budget amp!

A JJ and an EH are cheap enough (probably £20 in total) that I'm happy to give them a try before I throw the amp out of the window! It may well be a case of you get what you pay for and if I want a quality amp, I'll have to pay quality prices. It's a shame because it does do great tone at bedroom volumes, just not a smooth, consistent tone.

I was thinking of trying out a Marshall DSL15H, but my local shop doesn't stock it and the man there says it's because they're crap (cheap Vietnamese made).
 
Sovteks are usually a pretty good brand. Russian tubes are good. Maybe you have some bad ones.

The new DSL's are too new for your shop guru to know that they're crap just because they're made by asian children in sweatshops. I've played the bigger new DSL's and they sound fucking awesome. They seem to me to be good quality. Marshalls aren't typically known for sturdy build quality, but the knobs and switches all felt pretty solid.
 
jonny deep said:
.......The man in the shop told me that this is common in low power amps when you start to push the tubes.
Click to expand...

I've never seen a Fender Champ do this, being a low power amp.

jonny deep said:
.......I've researched online and found others with the same issue....... some say that it's to be expected in mass produced, low cost amps like this (i.e. they're very hit and miss) and can't be solved.
Click to expand...

See Fender Champ, Princeton, Orange Tiny Terror, Epiphone Valve Junior, etc.

jonny deep said:
.......So, I've decided to try a tube swap before I give up on the amp. My online research suggests that a JJ ECC83s 12AX7 tube in slot 1 and an EH 12AX7 tube in slot 2 is the best combination.
Click to expand...

Cheap and easy. May actually solve the problem.

jonny deep said:
.......Do I need to consider matching or biasing?
Click to expand...

You can, even though it is a purported Class A circuit. If you have a decent tech, he can possibly raise R4 to 150Ω. This may do the trick so more tube choices will work for you. If the result is too drastic, try changing R31 and R32 to a not necessarily matched pair of 47KΩ resistors.
People are spending $500 to have techs do a massive 'upgrade' to their Night Train. And this is for an amplifier that was $500 new, so changing just a few resistors shouldn't be an issue, especially if the results make you happy.
 
if you're changing only preamp tubes you're not gonna rebias them.

It's not impossible that you have a couple of noisy tubes so try replacing them.
 
Do you have a lower gain twin-triode tube to try in one of those slots (the one that's the preamp, assuming the other one is doing something else)? Like a 12AY7, 12AT7 (noisy, often), or something? In some of these newer amps, it seems like the power stage is getting slammed by the preamp stage, and the key is to weaken the signal going to the power stage a little bit.

Disclaimer - I have no idea what I'm saying - I just noticed that in some of my amps, particularly the newer ones, and both of the little Vox ones that I have (not including that model - I don't have that one), I got a fizzy/farty attack, and using usually 12AT7s (I got a lot of them for cheap, and most of those were too noisy, but some not), solved the problem.

I used to think that the preamp was too hot for the power tubes - usually EL84s, and I was trying to get beefier EL84s without much success. Now I think maybe there's some solid state circuitry in the power stage that's clipping - that's really what it sounds like.
 
I've got an old silver face Fender Champ that used to sound horrible. A few moments after you fire it up it would spew out a massive static crackle. I swapped the Fender ECC83 for a Russian Sovtek 12AX7. Now it's just as quiet as any of my other amps and sounds great.
 
ranjam said:
I've never seen a Fender Champ do this, being a low power amp.



See Fender Champ, Princeton, Orange Tiny Terror, Epiphone Valve Junior, etc.



Cheap and easy. May actually solve the problem.



You can, even though it is a purported Class A circuit. If you have a decent tech, he can possibly raise R4 to 150Ω. This may do the trick so more tube choices will work for you. If the result is too drastic, try changing R31 and R32 to a not necessarily matched pair of 47KΩ resistors.
People are spending $500 to have techs do a massive 'upgrade' to their Night Train. And this is for an amplifier that was $500 new, so changing just a few resistors shouldn't be an issue, especially if the results make you happy.
Click to expand...

Thanks mate - changing resistors is rather more drastic than I was envisaging and way beyond my knowledge and experience, but might be my next step if tubes don't fix my issue.
 
Lt. Bob said:
if you're changing only preamp tubes you're not gonna rebias them.

It's not impossible that you have a couple of noisy tubes so try replacing them.
Click to expand...

Thanks Bob, that's my current plan. It's quite a cheap thing to try, so well worth a go, IMHO.
 
snow lizard said:
I've got an old silver face Fender Champ that used to sound horrible. A few moments after you fire it up it would spew out a massive static crackle. I swapped the Fender ECC83 for a Russian Sovtek 12AX7. Now it's just as quiet as any of my other amps and sounds great.
Click to expand...

Lol, mine currently has Sovteks, supposedly. Maybe the other tube types mentioned above is the answer.

Thanks for the input, everyone, it's all a great help!!!
 
jonny deep said:
I took it into the shop and we determined it was indeed the amp and not my guitars (I could play other amps without the issue).

The man in the shop told me that this is common in low power amps when you start to push the tubes.

............

So, I've decided to try a tube swap before I give up on the amp.
Click to expand...


I'm kinda surprised the guy in the shop didn't try this when you were there.....?
Not talking about just trying out different brands for "flavor"...but that maybe you just have a bad tube that needed replacing.
I would think he would have done that first as a check........
 
It's also possible that the amplifier was designed and released with a circuit that makes finding tubes 'that work' difficult. Heck, you can spend days finding tubes for a Boogie, and their non-adjustable bias.
I used to have a 90's AC30 that no matter how many hundreds of quads of EL84's I put in, diming it I could see the one tube show a little cherry spot when I dug into my guitar. JJ, Sovtek, old stock GE, RCA, it didn't matter, it was always that one tube position and the plate would have that brief moment when you laid into a chord and I could actually see through the vent a little cherry spot show. Changing two bias resistors (Vox uses two 100Ω resistors in parallel for some strange reason) let me use virtually any tube I had, and no cherry plating.
This doesn't make me smarter than Vox (or anyone else), it just gave me a little experience in having no fear making a piece of gear work for me. If that means modifying it, or tweaking the circuit (or whatever), so be it. You can go the easy way, and use lower gain preamp tubes (as has been suggested), or go all out and make it so any tube will work, and the amp will sound to your liking.
 
they use two resistors in parrallel to double the voltage handling capabilities. They could have just used a larger 50ohm resistor but didn't for whatever reason. Sometimes it's just space requirements. Or maybe they had a huge inventory of 100ohm resistors in that voltage range.

What the OP describes sounds like a bad pre tube to me ...... biasing would have nothing to do with the issue if that is the problem and it's not that uncommon these days to get a crappy tube in an inexpensive amp.

I don't totally agree with the other stuff. I have two Mesas ....... pretty much any tube I stick in there works fine. Obviously if you ran into tubes showing cherry on the plates that's an issue but I've never had it happen.

That does remind me that back in the day we would simply turn the bias until the plates glowed a bit and then back it off until it just went away. :D
Not very precise!
 
Apparently there's '50 shades of gray' (who knew?), so who knows what someone's 'fizzy' or 'rattly' means. It could also be the signal driving the tubes into cutoff, since it only happens at medium gain settings. That makes me believe that it could be a bias problem. Not related, but a side story; an amplifier I built had that same problem (assuming we're talking 'grey' and not 'gray'), and a long time later I learned the output coupling capacitors I used were too big in value, causing 'blocking distortion'. Live and learn. All I was doing was trying to get more bass response. But this only happened on low bass notes, so I should have known. If jonny's problem is all over the frequency range, then I'm likely wrong. But if it's bass notes at high volumes causing problems, think tube bias and blocking distortion. For sure try tubes first (fast and cheap), but have a 'Plan B' if that isn't the cause.
 
ranjam said:
Apparently there's '50 shades of gray' (who knew?), so who knows what someone's 'fizzy' or 'rattly' means. .
Click to expand...

^^^^^ this ^^^^^^

It's always hard to completely know what someone means when they describe a sound. I might hear it and go,"Oh yeah ..... that's a power tube issue" or you might hear it and say, "Wow ..... I've never heard that described as a rattle"
It's hard to know sometimes.
 
Replace same tubes which are in the stock. Also tubes work for about 600 hours. After that they require replacement
 
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