I need new tubes... make some recommendations!

[jndietz]

Hey everyone... I own a B-52 ST6012 amplifier with Vintage 30s. I am interested in changing the tubes because 1) I bought the amp used and still has the same tubes and 2) right now I feel the amp has entirely too much gain. What do you guys recommend for all of the following:

Power: 2 – 6L6 / 5881
Preamp: 5 – 12AX7
Reverb: 1 – 12AT7
Rectifier: 1 – 5AR4

Thanks in advance everyone...

[eyema_believer]

Originally Posted by jndietz

Hey everyone... I own a B-52 ST6012 amplifier with Vintage 30s. I am interested in changing the tubes because 1) I bought the amp used and still has the same tubes and 2) right now I feel the amp has entirely too much gain. What do you guys recommend for all of the following:

Power: 2 – 6L6 / 5881
Preamp: 5 – 12AX7
Reverb: 1 – 12AT7
Rectifier: 1 – 5AR4

Thanks in advance everyone...

I would try buying 2 or three 12AT7s or 12AU7s and subbing them in different spots in the preamp. You'll have to try them in different spots, to see where they make the change you want. These have somewhat less gain than the 12AX7s, and will be a direct replacement for you. I wouldn't worry about the power tubes; those 6L6s won't distort until your ears bleed.

Peace!

~Shawn

[dementedchord]

Originally Posted by eyema_believer

I would try buying 2 or three 12AT7s or 12AU7s and subbing them in different spots in the preamp. You'll have to try them in different spots, to see where they make the change you want. These have somewhat less gain than the 12AX7s, and will be a direct replacement for you. I wouldn't worry about the power tubes; those 6L6s won't distort until your ears bleed.

Peace!

~Shawn

+1...


trying at's or au's is a great idea here... as to the output tubes... if there's a degredation from age as you suggest... then the outputs are the ones to change... the pre-tubes can last for ages.... and check into rebiasing if you do change the outputs....

[ocnor]

Originally Posted by eyema_believer

I would try buying 2 or three 12AT7s or 12AU7s and subbing them in different spots in the preamp.

12AT7s and 12AU7s draw more current and are NOT direct replacements for 12AX7s in all amps. Also it's not always immediately apparent that the amp is being damaged.

[cobradenim]

www.eurotubes.com

[antichef]

Originally Posted by ocnor

12AT7s and 12AU7s draw more current and are NOT direct replacements for 12AX7s in all amps. Also it's not always immediately apparent that the amp is being damaged.

yeeks!! what happens?

[ErichS]

This place has some good reviews and decent prices for tubes

http://thetubestore.com/

[eyema_believer]

Originally Posted by ocnor

12AT7s and 12AU7s draw more current and are NOT direct replacements for 12AX7s in all amps. Also it's not always immediately apparent that the amp is being damaged.

Which explains why they have more headroom, I suppose. I will edit my post. Thanks for the heads-up.
Sorry to the original poster for making a recommendation that had been made to me and worked fine for me, but potentially could damage an amp.

Peace!

~Shawn

[eyema_believer]

Well, for some reason I can't edit my previous post about 12AU7s and 12AT7s. If someone in the future reads this shaky advice, PLEASE read this entire thread before proceeding, paying careful attention to this warning:

12AT7s and 12AU7s draw more current and are NOT direct replacements for 12AX7s in all amps. Also it's not always immediately apparent that the amp is being damaged.

[dementedchord]

Originally Posted by ocnor

12AT7s and 12AU7s draw more current and are NOT direct replacements for 12AX7s in all amps. Also it's not always immediately apparent that the amp is being damaged.

and yet it seems the book i have here lists them as lower than ax7's... even if we assume that there's some varience from brand to brand one would still wonder what problems you experienced...

[ggunn]

Originally Posted by dementedchord

and yet it seems the book i have here lists them as lower than ax7's... even if we assume that there's some varience from brand to brand one would still wonder what problems you experienced...

I don't think that there is a direct correlation between the gain of a tube and the current it consumes. That said, it's kind of hard to imagine that a preamp tube drawing a little more current could hurt (I presume) the power transformer, since the current consumed by a preamp tube (I'm pretty sure) is small compared to that drawn by the power tubes. In most/all tube amps, the preamp and power tubes pull their current from the same tap on the power tranny.

[dementedchord]

Originally Posted by ggunn

I don't think that there is a direct correlation between the gain of a tube and the current it consumes. That said, it's kind of hard to imagine that a preamp tube drawing a little more current could hurt (I presume) the power transformer, since the current consumed by a preamp tube (I'm pretty sure) is small compared to that drawn by the power tubes. In most/all tube amps, the preamp and power tubes pull their current from the same tap on the power tranny.

agreed... though he seemed worried about the current handling of the heater tranny specificlly... or did i miss read something again???

[ocnor]

Over at the Carvin boards, some guys with way more knowledge than I have, stated that certain resistors in some amps may not be rated for the extra current draw. They also showed pictures of toasted resistors and circuit boards which resulted from using 12at7s. Another person stated that his amp fried when he substituted 12au7s in place of 12ax7s. Some amps may be fine with the substitutions but just make sure before you do it.

[Corndog]

I swapped out the 12at7 for a 12ax7 in my '77 Fender Super Twin...is that bad??? I never trusted anything with tits or tubes.

[ocnor]

Originally Posted by Corndog

I swapped out the 12at7 for a 12ax7 in my '77 Fender Super Twin...is that bad??? I never trusted anything with tits or tubes.

If you put a 12ax7 in a circuit designed for a 12at7 then you had better keep the fire extinguisher handy.

[jndietz]

How about this question... where can I get myself a good multimeter?

[eyema_believer]

double post

[eyema_believer]

triple post!!

[eyema_believer]

[QUOTE=ocnor;3014561] If you put a 12ax7 in a circuit designed for a 12at7 then you had better keep the fire extinguisher handy. [QUOTE]

So you're saying that if you put a tube that draws less current in place of one that draws more current you're creating a distressful situation inside the amp? Not that I know anything about anything.....but usually stuff only gets too hot when you draw more current than a circuit is designed for....dunnit?

[antichef]

I use a 12AT7 in my 1965(ish) Epi 101 single EL84 amp. All the 12AX7s I tried tended to overpower the EL84 and it got farty sounding. Much better with the 12AT7 -- is it as simple as burning up a resistor? I can fix that

[eyema_believer]

Originally Posted by antichef

I use a 12AT7 in my 1965(ish) Epi 101 single EL84 amp. All the 12AX7s I tried tended to overpower the EL84 and it got farty sounding. Much better with the 12AT7 -- is it as simple as burning up a resistor? I can fix that

I have a Kalamazoo Model One single ended amp with a single EL84 output tube, and I did the same thing. It worked wonders!

[ocnor]

Originally Posted by eyema_believer

So you're saying that if you put a tube that draws less current in place of one that draws more current you're creating a distressful situation inside the amp?

No I said that if you put a tube that handles less current[12ax7] into a circuit meant for a 12at7 that is feeding it more current that you will cook the 12ax7 causing other components to fail.

Originally Posted by antichef

I use a 12AT7 in my 1965(ish) Epi 101 single EL84 amp. All the 12AX7s I tried tended to overpower the EL84 and it got farty sounding. Much better with the 12AT7 -- is it as simple as burning up a resistor? I can fix that

Yes resistors are easy to replace. But in modern amps with printed circuit boards if you burn the traces it becomes a little more tricky to repair.

[dgatwood]

Originally Posted by ocnor

No I said that if you put a tube that handles less current[12ax7] into a circuit meant for a 12at7 that is feeding it more current that you will cook the 12ax7 causing other components to fail.

You folks are all kidding, right?

1. There's exactly one rating that matters in preamp tubes (assuming the pinouts are the same), and that's the voltage.

2. The tube heater is a resistive load and will draw exactly as much current as it needs to draw. No more, no less. So there's no difference in tube life expectancy caused by substituting a device with lower or greater current draw. That's like asking whether a light bulb will burn out sooner if you hook it up with a heavier gauge lamp cord. It won't....

3. If your amp can't produce enough current for the tube heater, it will result in a voltage drop and the wires will heat up and the tube's sound won't be as good (or if the current limit is caused by a fuse, it will blow the fuse). Since we're just talking about a 12V current source, though, I can't imagine an amp design not being able to provide enough current. We're dealing with current in the hundreds of milliamps here. It's peanuts. The cheapest, smallest regulator or Zener you could buy should handle that little trickle....

4. All of the 12A*7 tubes are designed for a 150 mA, 12.6V supply. While there is individual variation from manufacturer to manufacturer, if your amp doesn't provide at least 150 mA, it is broken by design, and if a tube draws more than that, it is defective. In other words, the supply for a 12AX7 has to provide exactly the same voltage and current as the supply for a 12AY7 or a 12AT7 or a 12AU7 or....

In other words, you won't have any problem swapping around preamp tubes. You probably shouldn't be swapping power tubes without rebiasing, but you really can't go wrong swapping out preamp tubes as long as it's a 12A*7 or any other pin-compatible 12V tube (5965, 6072, etc.)....

One caveat: if the tubes happen to be arranged in a push-pull configuration, make sure you're using similar tubes for both sides or else you'll have a really weird output.

Originally Posted by ocnor

Over at the Carvin boards, some guys with way more knowledge than I have, stated that certain resistors in some amps may not be rated for the extra current draw. They also showed pictures of toasted resistors and circuit boards which resulted from using 12at7s. Another person stated that his amp fried when he substituted 12au7s in place of 12ax7s. Some amps may be fine with the substitutions but just make sure before you do it.

My bet would be a defective tube, but if not, Carvin should recall the amps. If they can't handle a 12AU7, you can pretty much guarantee that they can't handle a lot of 12AX7 models, either.

[Corndog]

My Twin has 6 6l6's and I've been told that I can take the 2 outside tubes out to tame the volume. Is this ,in fact,correct???

Sorry to hi-jack thethread BTW...

[darrin_h2000]

I dont think that the 12ax7 will pull more current to get the higher gain...its saturation point is much lower than the tubes that will be cleaner 12at7 so they in turn must have that point higher requiring more voltage which is why PC boards on new amps can get hotter than they should...my tube stuff for the most part has no PC boards inside...but it is also all from the 1960s...and things were made very different back then.