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Swapping tubes in a hybrid amp
- Thread starter MrCash
- Start date
In my experience, you have to try it, use some good NOS tubes & some current production tubes, and it usually is the first tube in the preamp signal chain
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
It depends almost entirely on the type of circuits used in the amp. Some circuits are tolerant of widely varying tube parameters, yielding consistent tone and some are not.
Just because your tubes are Chinese does not automatically mean that they are cheap and generic. The Chinese have over the years produced some of the very best tubes in the world... and of course some that were not so good. It really depends on which tubes you are talking about. The Chinese used (and supplied) tubes for many legacy eastern block military products, so "it depends".
Just because your tubes are Chinese does not automatically mean that they are cheap and generic. The Chinese have over the years produced some of the very best tubes in the world... and of course some that were not so good. It really depends on which tubes you are talking about. The Chinese used (and supplied) tubes for many legacy eastern block military products, so "it depends".
Some tubes hum, are hissy, crackle and pop. Changing them can help. Some of this can also be due to loose or oxidized tube pin to tube socket contacts. Signs of when to change a tube are listed here: Tubes | TalkBass.com.
Life is never as uncomplicated as you'd like it to be.
Life is never as uncomplicated as you'd like it to be.
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I am not an engineer, but as agedhorse mentioned, it depends on the circuit design of the amp in question. One factor seems to be whether the amp uses a starved plate approach or a high/full voltage approach. I think it's generally the case (again, I'm not an engineer) that in a starved plate design, the tube really has much less influence on the final tone of the amp, so tube rolling in a starved plate type amp will likely have less noticeable effect. With a high voltage design, its more likely you will notice tone/character changes ... depending on the tube (of course).
All that being said, I have rolled preamp and driver tubes in my Walkabout (hybrid with a high voltage approach) and have definitely heard the difference between different 12AX7 preamp tubes. If the amp in question has a driver tube, rolling different tubes in that position can also have an impact on tone/character. Keep in mind, the changes are not "night & day", they tend to be subtle, but if you are pretty attuned to the sound of your amp, you should notice differences.
All that being said, I have rolled preamp and driver tubes in my Walkabout (hybrid with a high voltage approach) and have definitely heard the difference between different 12AX7 preamp tubes. If the amp in question has a driver tube, rolling different tubes in that position can also have an impact on tone/character. Keep in mind, the changes are not "night & day", they tend to be subtle, but if you are pretty attuned to the sound of your amp, you should notice differences.
- Feb 12, 2006
- 61,003
- 5
- 220,809
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Plate voltage has very little to do with the tone PROVIDED the circuit is designed specifically for the curves associated with lower plate voltage. There are maybe a dozen interacting variables that all go hand in hand. You can't just change one and assign a cause/effect without scaling the rest of the design's remaining variables.
It's no different than gain structure, if you scale stage down by 3dB, then sure it will sound quieter but if you scale another stage up by 3dB the results will be identical to the original scenario.
It's important to understand that there are many factors that go into how a circuit performs, and that there are in fact circuit techniques that can be used to reduce the impact of some of these variables. Why would a designer want to do this? Because most manufacturers do not want to ship an amp that is so dependent on a specific tube tolerance (that can not be controlled any other way than during tube fabrication) that their amp might sound crappy with a high percentage of the available tubes on the market. By doing this, it's possible to improve the overall tone for the majority of players most of the time.
It's no different than gain structure, if you scale stage down by 3dB, then sure it will sound quieter but if you scale another stage up by 3dB the results will be identical to the original scenario.
It's important to understand that there are many factors that go into how a circuit performs, and that there are in fact circuit techniques that can be used to reduce the impact of some of these variables. Why would a designer want to do this? Because most manufacturers do not want to ship an amp that is so dependent on a specific tube tolerance (that can not be controlled any other way than during tube fabrication) that their amp might sound crappy with a high percentage of the available tubes on the market. By doing this, it's possible to improve the overall tone for the majority of players most of the time.
In this case it's a bugera bvp5500. The svt 3 pro alike but not an exact clone in circuitry.
I assume it's not starved plate.
And has the tube voltage control knob like the svt 3 pro.
The tubes I can't fully identify they say bugera but they look just like the Chinese generic short plate 12ax7's of course there is a few version of that tube.
It does have a nice front end, very usable gain and overdrive etc. But it sounds a little bit restricted like if it had a tube with more oomph it might open up a little more.
I assume it's not starved plate.
And has the tube voltage control knob like the svt 3 pro.
The tubes I can't fully identify they say bugera but they look just like the Chinese generic short plate 12ax7's of course there is a few version of that tube.
It does have a nice front end, very usable gain and overdrive etc. But it sounds a little bit restricted like if it had a tube with more oomph it might open up a little more.
Here is a visual. The springs are putting tension on the microphone element, holding it in position in space. If one spring has a different tension, the balance is changed and the element's position changes, affecting the tension of the other springs.
Similarly, interacting factors in a tube stage design affects how the tube operates. How it sits in relation to it's operating curves. How it performs when an AC signal is applied and an amplified version of the signal is produced.
The link below illustrates the bias point of a tube and how shifting the bias point affects the output in relation to the input signal. Ideally if a tube is biased in a linear region of it's operating curve, a small input will produce a scaled up, amplified output with no distortions. If the tube is biased closer to a non-linear region of it's operating curve, the output will be distorted. In these cases, tube rolling can make a difference. Of course, real world performance is more complicated.
[Invalid or Expired Link Removed]
Similarly, interacting factors in a tube stage design affects how the tube operates. How it sits in relation to it's operating curves. How it performs when an AC signal is applied and an amplified version of the signal is produced.
The link below illustrates the bias point of a tube and how shifting the bias point affects the output in relation to the input signal. Ideally if a tube is biased in a linear region of it's operating curve, a small input will produce a scaled up, amplified output with no distortions. If the tube is biased closer to a non-linear region of it's operating curve, the output will be distorted. In these cases, tube rolling can make a difference. Of course, real world performance is more complicated.
[Invalid or Expired Link Removed]
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A couple more things to mention about NOS tubes.
1) Most of them aren't really NOS. It has been almost three decades since the last vacuum tubes were made in America, and in the intervening time, most of the best of the old stock has been spoken for.
2) New amps are generally designed to work with new tubes. I think it was @agedhorse who mentioned that the GB Shuttle and Streamliner amps were made to work best with the tubes of the time.
1) Most of them aren't really NOS. It has been almost three decades since the last vacuum tubes were made in America, and in the intervening time, most of the best of the old stock has been spoken for.
2) New amps are generally designed to work with new tubes. I think it was @agedhorse who mentioned that the GB Shuttle and Streamliner amps were made to work best with the tubes of the time.
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Right, there are a lot more variables involved (including plate voltage versus plate load versus gain)
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Right, (IMO) it's foolish to design a new product that can't use the tubes available without a serious reduction in performance. Designers at larger (I would expect) have access to tube data distribution over a large number of tubes and this SHOULD help guide design choices to give the player the bast combination of performance versus availability. There's nothing like looking at the test reports from say 5000 tubes to sober one's idealistic attitude, and there is absolutely nothing that can be done to change this as it's part of tube fabrication in the 21st century (no matter how much we would like to).
i prefer older mil spec tubes ...
or newer JJ / Tesla
for bass , i like longer plates .. ! tight bass
or newer JJ / Tesla
for bass , i like longer plates .. ! tight bass
- Feb 12, 2006
- 61,003
- 5
- 220,809
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
no argument here, particularly not with you agedhorse. I have just read in more than once place, that amp manufacturers who use a starved plate design are most often going that route for more or less marketing purposes - to say that their amp is a "tube amp", which it would be technically, but that the reality is that preamp tubes used in this approach are much less noticeable or meaningful in the ultimate tone of the amp vs high voltage designs.
Even with my limited technical understanding, I get that there are many ways to skin the amp design cat, and none are specifically wrong or right per se .. just different ways to get to the goal.
Al Kraft
Supporting Member
- May 2, 2016
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I have rarely heard a significant difference (like night and day) between properly functioning tubes in a preamp section of bass amp that had a solid state amp section. Now experimenting with different model/part number tubes (and I'm not talking about a US versus European P/N for essentially the same tube) occasionally produces noticeable differences, but you're now operating outside of the original design specification envelope. YMMV!
I do feel very confident saying that China, Russia and many other countries went on maturing and perfecting tube manufacturing and associated technologies decades after we in the US all but abandoned it and moved into solid state. At one time there was an airborne Soviet radar system and associated avionics that were both one of the world's most powerful/effective and also heavily tube based. Tube technology was also thought to be much less susceptible to EMI/P effects in a nuclear confrontation and more tolerant of temperature extremes.
The bottom line is that just because an older technology is coming from overseas sources, don't jump to a conclusion that its is "yesterday's third world junk". I know plenty of older pilots who will tell you that US solid state (or tube) wasn't an automatic advantage over foreign tube based systems.
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I do feel very confident saying that China, Russia and many other countries went on maturing and perfecting tube manufacturing and associated technologies decades after we in the US all but abandoned it and moved into solid state. At one time there was an airborne Soviet radar system and associated avionics that were both one of the world's most powerful/effective and also heavily tube based. Tube technology was also thought to be much less susceptible to EMI/P effects in a nuclear confrontation and more tolerant of temperature extremes.
The bottom line is that just because an older technology is coming from overseas sources, don't jump to a conclusion that its is "yesterday's third world junk". I know plenty of older pilots who will tell you that US solid state (or tube) wasn't an automatic advantage over foreign tube based systems.
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Bugera tubes would fall in the generic category, poor QC, I had a V5 and the 12ax7 was microphonic out of the box. Swapping it made a big difference.
My sadly stolen SWR350, I had swapped the tube for a vintage 7025 (in octogon, rca I believe), which enabled me to overdrive the preamp without it farting out. Little did the theif know the tube inside was worth half of what the amp was worth. The audix d4, along with the monster cables tucked in the back of the rack, not to mention akg UHF and korg tuner in the rack... Ouch.
Anyway, you could definitely improve on bugera tubes, but maybe you lucked out and got "good ones"
Also try changing position of your tubes, perhaps the one in v3 is better suited for v1 etc... Bugera certainly didn't stake much pain there, they just stuck em in there.
My sadly stolen SWR350, I had swapped the tube for a vintage 7025 (in octogon, rca I believe), which enabled me to overdrive the preamp without it farting out. Little did the theif know the tube inside was worth half of what the amp was worth. The audix d4, along with the monster cables tucked in the back of the rack, not to mention akg UHF and korg tuner in the rack... Ouch.
Anyway, you could definitely improve on bugera tubes, but maybe you lucked out and got "good ones"
Also try changing position of your tubes, perhaps the one in v3 is better suited for v1 etc... Bugera certainly didn't stake much pain there, they just stuck em in there.
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
It may have simply been that the microphonics tube in your V5 was defective and nothing more complicated than that.
ALL tubes fall into a wide range of operational parameters. Changing tubes and expecting an improvement without knowing and understanding the impact of these parameter variations is purely luck.
ALL tubes fall into a wide range of operational parameters. Changing tubes and expecting an improvement without knowing and understanding the impact of these parameter variations is purely luck.
Al Kraft
Supporting Member
- May 2, 2016
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- Mesa Boogie beta product tester and player support
There is good reason people are willing to pay more for tubes that are extensively tested and closely matched over just using whatever you get out of whatever boxes are on the shelf. Some circuit designs are more forgiving of variation than others, but very few circuit designs in amplification are at all forgiving of excessive microphonics in my experience.
Working with tubes reminds me of building with natural materials like wood that tend to have their own characteristics despite all efforts to make them uniform. Solid state components remind me of synthetic materials which usually have well controlled, consistent, stable and predictable characteristics designed in from their inception. Each approach has its pros and cons. In the end degrees of variation you can tolerate and the compromises you need to be willing to accept/work around need to be weighed against the benefit you're looking for.
In today's world we tend to forget about the level of variation inherent in some older technologies as we've become accustomed to a high degree of uniformity, repeatability and reliability in the age of high tech solid sate components.
Working with tubes reminds me of building with natural materials like wood that tend to have their own characteristics despite all efforts to make them uniform. Solid state components remind me of synthetic materials which usually have well controlled, consistent, stable and predictable characteristics designed in from their inception. Each approach has its pros and cons. In the end degrees of variation you can tolerate and the compromises you need to be willing to accept/work around need to be weighed against the benefit you're looking for.
In today's world we tend to forget about the level of variation inherent in some older technologies as we've become accustomed to a high degree of uniformity, repeatability and reliability in the age of high tech solid sate components.
- Apr 13, 2006
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- If you heard me play, you'd stop reading what I write.
I had a Tubeworks head with a single 12ax7; it sounded the same to me no matter what I put in it. Then I had a Demeter VTBP 201, with a 4-stage (2-tube) preamp and no solid state circuitry in the signal path. This one, predictably, was responsive to tube changes. I didn't geek out enough to try to hear the effect of different tubes in the different sockets; I just tried pairs of identical tubes. With a preamp like this, that has a very limited eq, I think it can be useful to roll tubes to tweak your sound.
It can also be useful on preamps that are designed to be overdriven ... you may be able to change the overdrive character. If you switch to a compatible but different tube (like from 12ax7 to 12au7) you can change the amount of clean headroom. Unfortunately neither of my tube preamps was designed for overdriven tones, so I didn't get to play with this.
I was lucky enough to have a friend with an all-tube preamp on his stereo, who had just gone on an internet tube-buying bender. He sent me a bunch to try out, including some very expensive NOS mullards. Fortunately, the ones I really liked were some RCA black plates from 60s, which were quite inexpensive at the time. Unfortunately, those days are over ... they cost a fortune now.
It can also be useful on preamps that are designed to be overdriven ... you may be able to change the overdrive character. If you switch to a compatible but different tube (like from 12ax7 to 12au7) you can change the amount of clean headroom. Unfortunately neither of my tube preamps was designed for overdriven tones, so I didn't get to play with this.
I was lucky enough to have a friend with an all-tube preamp on his stereo, who had just gone on an internet tube-buying bender. He sent me a bunch to try out, including some very expensive NOS mullards. Fortunately, the ones I really liked were some RCA black plates from 60s, which were quite inexpensive at the time. Unfortunately, those days are over ... they cost a fortune now.
