Preamp tubes

[beans-on-toast]

This explains, in part, why standby switches are in amps.

https://peavey.com/support/technotes/hartley/Chapter_6.pdf

In general, you want a delay that allows the heater to come up to temperature allowing electrons to boil off the plate and application of the high voltage power supply. There are different ways of designing in this delay, a standby switch is one of them. Some tube rectifiers have a slow turn on that give the other tube heaters enough time to come up to temperature. Inrush current limiters can be used. Relays with delays can be used.

The length of the recommended warmup time varies depending on the tubes. Recommendations found in tube data sheets are intended to promote long service life.

 

[agedhorse]

This explains, in part, why standby switches are in amps.

https://peavey.com/support/technotes/hartley/Chapter_6.pdf

In general, you want a delay that allows the heater to come up to temperature allowing electrons to boil off the plate and application of the high voltage power supply. There are different ways of designing in this delay, a standby switch is one of them. Some tube rectifiers have a slow turn on that give the other tube heaters enough time to come up to temperature. Inrush current limiters can be used. Relays with delays can be used.

The length of the recommended warmup time varies depending on the tubes. Recommendations found in tube data sheets are intended to promote long service life.

There are two different factors in the advantage of warm-up time. The first is the possibility of cathode stripping, which may be an issue or it may not (the data is not as clear cut as it might appear), the other difference is to slow down the mechanical expansion & contraction of the tube's internal elements to decrease the stress.

In reality, I suspect that it's really a bit of both together that are responsible for the increase in tube life by using a warm-up standby process. The bigger the tubes, the more pronounced the effect from the data I have seen.

 

[BurningSkies]

Beware the (entire) tube reseller market, it's full of snake oil, mythology, fanciful stories and dialog designed specifically designed to separate you from as much money as possible.

While there are some honest folks in that business, it's very hard to make a living without joining the fray of the above and buyers are easily duped by a good story that they want to believe.

I went from the stock (tested) Shuguang tubes in my preamp to: RCA blackplate NOS/JAN, Sylvania NOS/JAN and later a supposed Tungsol brownbase NOS. All of which failed with fairly low hours. I ended up going back to the original tubes (and also got a replacement set from the same source), and haven't had a failure since...with over 100 shows plus many hundreds of hours of additional play time on them.

 

[40Hz]

All I'm doing is quoting the manual.
I guess You are right. It depends on whether you have read the manual. After all there is a bunch of garage amp builders who say stand-by switches aren't necessary. @agedhorse, I believe that if you include stand-by switches in your designs, then I am sure you provide minimum warm up times. Therefore, you do not belong on my unwritten list of garage amp builders.

I get the distinct impression you have no idea who @agedhorse is if you're making a comment like that.

 

[ahc]

So what you're indeed saying is that if we go ahead and remove one of the ways in which these tubes are inherently different, they become more the same, right? Isn't that how your statement reads? That if we make them the same artificially, that they become the same. Why bother saying that? What you're really saying is purely theoretical, and I can't help but notice that. It is also 100% fact, yes. If we build them all identically, and use them all in the same amp, and adjust the parameters identically, and use the same guitar and cab, play the same song, at the same time, then naturally they will all sound the same, presumably. Not only that, but someone would think something weird is going on.

Do you play guitar? If so, don't you notice the differences in sound from each tube? From each amp? Cab? Do you sample them? I'm speaking very objectively, here. I mean to exactly pinpoint that there is a difference between someone who can engineer, design, and build an amp, and someone really listening to tone quality and nuance. I'm NOT saying you lack one or the other. Not at all. I am indeed saying that there is a difference in the processes in both programs, and that a person built for one part (design, engineer) may not even care about the other (how it sounds).

Aren't you supposed to be telling me that V1 is the most critical, because that's the one with the biggest effect to the signal downstream?

You have a fairly impressive length of time with equipment, and I'm sure you put all that stuff in your signature to get someone to stroke your ego over it, and you're also trying to tell me that changing tubes will have very small, probably inaudible differences? Are you really trying to tell me that even with this graph showing subtle differences, that all tubes are almost identical? Granted, they follow an admittedly VERY SIMILAR curve, but NOT IDENTICAL. There's ONE difference. How do they sound? JUST LIKE WITH ANYTHING EVER MADE EVER, EVER, they aren't identical. Some may have been built by folks hung over on Monday morning, whilst others fail the QC standards.

Why so many different brands? Even if only a few manufacturers? Why do some amp manufacturers use exclusively one brand? Don't tell me it's all because of sponsorship and financial arrangements. There had to be a reason to begin negotiations in the first place. If a tube manufacturer made a million tubes for brand X amp builder, and they all sounded horrible (thereby proving that there are differences), brand X probably wouldn't care if they were offered at discount. Brand X would likely choose consistent and similar tubes that made their amps sound great, right? From one manufacturer. Because who knows how the others sound, bringing it right back around that each one can be subtly different. They're like tract homes, and every one has subtle differences, right? Color, floor plan, I mean really.

That is all.

 

[Wasnex]

+1

For me, there really is a tone difference with *SOME* tube swap-outs in *SOME* preamps. Key word is "some." I think there are many scenarios where tube rolling doesn't seem to make much difference in tone. That could be due to the particular tubes that are being swapped out, or the preamp circuit design, or a combination of both. I think because there are so many times when it doesn't seem to make much difference, that has led to the sentiment that exists today regarding tube rolling.

My perspective is, try swapping out tubes to see if it makes a noticeable difference. If it does, cool! If it doesn't, then you now have information you didn't have before, which is helpful.

Over the last year, I have rolled tubes into around 10 bass and guitar amps. The tonal contour of each tube was fairly consistent from amp to amp but the degree of change varied significantly. I was able to tailor the sound more to my tastes in all amps with 12AX7s. Among 12AX7 equipped amps, my Aguilar DB359 was probably the least responsive to tube changes, but the improvement was enough to justify leaving a brand new Mullard ECC83 and JJ ECC803S in the amp. The amp is now tighter and louder...some of this should probably be attributed to adjusting and achieving a better balance with the Phase Inverter.

The amp that showed almost no responsiveness to tube changes was my CTM300. This amp uses 12DW7s in V1 and V2, and comes stock with JJs. I rolled NOS GE and Ratheon 12DW7s into V1 and V2, and noted minor gain differences and maybe just a touch more openness in the top end. The tonal differences weren't enough to justify leaving the NOS tubes in the amp. I suspect the reason for this experience is because 12DW7s are not as varied as 12AX7s, but it could be that the circuit is oblivious to tube changes.

Some changes I have noted with tube rolling include modified 1) gain, 2) tonal contour (EQ/voicing), and 3) OD characteristics. While tubes do seem to have a basic personality profile, they don't behave exactly the same in each circuit. Because of this, it is not possible to rely exclusively on one tube model to bring out the best of each amp. Some experimentation is required for best results and often using a combination of tube models is preferred.

I have always been really fixated on the way instruments sound, so tube rolling is just good fun for me. That doesn't mean everybody should do it. For the record, I used to really enjoy tweaking my sound with a parametric EQ as well. Tube amps typically have very basic EQ sections so you really can't tweak the basic sound very much. IMHO, tube rolling allows you to make subtle changes to the amp's voicing that would not otherwise be possible.

 

[beans-on-toast]

There are two different factors in the advantage of warm-up time. The first is the possibility of cathode stripping, which may be an issue or it may not (the data is not as clear cut as it might appear), the other difference is to slow down the mechanical expansion & contraction of the tube's internal elements to decrease the stress.

In reality, I suspect that it's really a bit of both together that are responsible for the increase in tube life by using a warm-up standby process. The bigger the tubes, the more pronounced the effect from the data I have seen.

The data sheets of some transmiting tubes recommend reducing the heater voltage to 80% of nominal to extend tube life if the standby time is longer than a prescribed duration. Transmitting tubes are more expensive than many so if it helps reduce cathode stripping, it's a good thing.

 

[Drgonzonm]

I get the distinct impression you have no idea who @agedhorse is if you're making a comment like that.

@agedhorse is designer of amps, I do not know what tube amps @agedhorse has designed, and at this point it not necessary for some one to list them. All I'm saying, is if @agedhorse puts a standby switch in one of designs, I believe he has a reason. As a designer, I also believe @agedhorse would include a minimum warm up time. And post #62 supports my belief.
I would not be surprised to find out @agedhorse did build a few amps in the garage equiv.

 

[agedhorse]

So what you're indeed saying is that if we go ahead and remove one of the ways in which these tubes are inherently different, they become more the same, right? Isn't that how your statement reads?

Correct, by normalizing the variations between tubes to as close to the ideal range as possible, we eliminate the tubes and the unpredictable characteristics that they cause, as a reason for one amp sounding "good" and another of the same model sounding "bad". This way the distribution of amp production is skewed towards all amps sounding good while maybe a few don't sound "glorious" (I'm using hyperbole here intentionally)

That if we make them the same artificially, that they become the same. Why bother saying that? What you're really saying is purely theoretical, and I can't help but notice that. It is also 100% fact, yes. If we build them all identically, and use them all in the same amp, and adjust the parameters identically, and use the same guitar and cab, play the same song, at the same time, then naturally they will all sound the same, presumably. Not only that, but someone would think something weird is going on.

No, you are making assumptions about something that I did not say. This is not theoretical, but in fact a very practical application. There are many variables within an entire amp, what some designs try to do is reduce the span of the influence of the TUBE variables to try to achieve more consistent results over the entire production of amps be reducing the effects of the extremes of variables that can not be held constant it tube production. The amps from unit to unit may still have some differences, but they won't be large differences and a player trying one unit can have some confidence that another of the same model will sound reasonably similar. It's really no different the screening a batch of tubes to achieve tighter parameters.

Do you play guitar? If so, don't you notice the differences in sound from each tube? From each amp? Cab? Do you sample them? I'm speaking very objectively, here. I mean to exactly pinpoint that there is a difference between someone who can engineer, design, and build an amp, and someone really listening to tone quality and nuance. I'm NOT saying you lack one or the other. Not at all. I am indeed saying that there is a difference in the processes in both programs, and that a person built for one part (design, engineer) may not even care about the other (how it sounds).

I don't play guitar (keyboard player here), but I spent decades on the road as a FOH engineer dealing with exactly this, the very details of tone and translating these details into the FOH mix. So, I am probably as familiar with anybody with the nuances of tone with some demanding clients. We also spend a lot of time comparing and testing very fine details of every design. Listening tests are in fact a critical part of the process. The challenge I have is with the feel, but I have access to some top tier players who are excellent at helping me translate this to appropriate circuitry approaches.

Aren't you supposed to be telling me that V1 is the most critical, because that's the one with the biggest effect to the signal downstream?

Maybe, but maybe not. It depends almost entirely on the circuit used, and how it fits into the overall architecture of the amp. V1 can be a VAS, but it could be any number of other circuit topologies (or even stages... not all V1's are the virst tube in the signal path).

You have a fairly impressive length of time with equipment, and I'm sure you put all that stuff in your signature to get someone to stroke your ego over it, and you're also trying to tell me that changing tubes will have very small, probably inaudible differences? Are you really trying to tell me that even with this graph showing subtle differences, that all tubes are almost identical? Granted, they follow an admittedly VERY SIMILAR curve, but NOT IDENTICAL. There's ONE difference. How do they sound? JUST LIKE WITH ANYTHING EVER MADE EVER, EVER, they aren't identical. Some may have been built by folks hung over on Monday morning, whilst others fail the QC standards.

I put that stuff in my signature because I was told by the forum administers that I MUST include it in order to comply with the forum's terms of service and CUP. It has nothing to do with stroking anybody's ego.

I didn't say that changing tubes will have a "very small, probably inaudible difference". I said that it depends on the design of the amp, and that some designs intentionally minimize or normalize the wide range of tube differences in order to improve the overall consistency of their amplifier product.

I pointed out that the graph you posted shows that almost ALL of the shown differences would be somewhat insignificant when normalized for gain, but I also went on to indicate some other areas of potential differences that the graph does not show, which might be even more responsible for differences in sound.

Why so many different brands? Even if only a few manufacturers? Why do some amp manufacturers use exclusively one brand? Don't tell me it's all because of sponsorship and financial arrangements. There had to be a reason to begin negotiations in the first place. If a tube manufacturer made a million tubes for brand X amp builder, and they all sounded horrible (thereby proving that there are differences), brand X probably wouldn't care if they were offered at discount. Brand X would likely choose consistent and similar tubes that made their amps sound great, right? From one manufacturer. Because who knows how the others sound, bringing it right back around that each one can be subtly different. They're like tract homes, and every one has subtle differences, right? Color, floor plan, I mean really.

Good question... while there may be quite a few different "brands", if you were to look a little deeper into the tube manufacturing industry you would find that there are only a very few manufacturers and each of the few manufacturer has multiple brands which may be marketed in different ways. Manufacturers choose from a couple of manufacturers and generally strive for the highest reliability and consistency, along with low microphonics and self-noise from tube to tube over spans of tens of thousands of tubes. In a well designed circuit, there are relatively few brands of poor tubes, but there may be a wider variation between good and bad sounding tubes in some circuits. So, the answer is that it depends on the circuit, the specific priorities of the amp manufacturer, and in some cases the availability of a particular tube. Screening can only go so far in weeding out defective tubes also, so a tube that has a high long term failure rate may cause a manufacturer a lot of warranty costs (and customer aggravation) that they wouldn't otherwise have to deal with by using a higher reliability part.

 

[agedhorse]

@agedhorse is designer of amps, I do not know what tube amps @agedhorse has designed, and at this point it not necessary for some one to list them. All I'm saying, is if @agedhorse puts a standby switch in one of designs, I believe he has a reason. As a designer, I also believe @agedhorse would include a minimum warm up time. And post #62 supports my belief.
I would not be surprised to find out @agedhorse did build a few amps in the garage equiv.

Nope, other than prototypes, all my tube amp designs have been production models.

I like to see a minute or so of warm-up time, mostly for thermal equilibrium of the basic structures before the step increase in temperature caused by taking it out of standby and allowing plate current to flow.

I suppose that for many amps, the difference in tube lifespan is fairly small by doing so, but IME larger tubes like the KT-88 and 6550's might benefit more from this.

 

[Wasnex]

I went from the stock (tested) Shuguang tubes in my preamp to: RCA blackplate NOS/JAN, Sylvania NOS/JAN and later a supposed Tungsol brownbase NOS. All of which failed with fairly low hours. I ended up going back to the original tubes (and also got a replacement set from the same source), and haven't had a failure since...with over 100 shows plus many hundreds of hours of additional play time on them.

That sucks and it sounds like you were ripped off. The general expectation is for true NOS tubes to be more consistently close to design spec and to have a longer service life than current production tubes.

IMHO the Shuguang 12AX7s I have used were very good sounding tubes and I think they are tougher and more reliable (on average) than many of the recent New Sensor designs. I frequently prefer the sound of some of New Sensors offerings in V1, but often the decision is very close.

Sometimes the choice is a matter of choosing the preferred compromise. One tube might have better bass while the other has a nicer top end. Or one tube may sound better clean, while the other sounds better when pushed into OD. Or maybe you need a tube with less gain so your volume control works instead of going from off to too loud.

 

[SactoBass]

Over the last year, I have rolled tubes into around 10 bass and guitar amps. The tonal contour of each tube was fairly consistent from amp to amp but the degree of change varied significantly. I was able to tailor the sound more to my tastes in all amps with 12AX7s. Among 12AX7 equipped amps, my Aguilar DB359 was probably the least responsive to tube changes, but the improvement was enough to justify leaving a brand new Mullard ECC83 and JJ ECC803S in the amp. The amp is now tighter and louder...some of this should probably be attributed to adjusting and achieving a better balance with the Phase Inverter.

The amp that showed almost no responsiveness to tube changes was my CTM300. This amp uses 12DW7s in V1 and V2, and comes stock with JJs. I rolled NOS GE and Ratheon 12DW7s into V1 and V2, and noted minor gain differences and maybe just a touch more openness in the top end. The tonal differences weren't enough to justify leaving the NOS tubes in the amp. I suspect the reason for this experience is because 12DW7s are not as varied as 12AX7s, but it could be that the circuit is oblivious to tube changes.

Some changes I have noted with tube rolling include modified 1) gain, 2) tonal contour (EQ/voicing), and 3) OD characteristics. While tubes do seem to have a basic personality profile, they don't behave exactly the same in each circuit. Because of this, it is not possible to rely exclusively on one tube model to bring out the best of each amp. Some experimentation is required for best results and often using a combination of tube models is preferred.

I have always been really fixated on the way instruments sound, so tube rolling is just good fun for me. That doesn't mean everybody should do it. For the record, I used to really enjoy tweaking my sound with a parametric EQ as well. Tube amps typically have very basic EQ sections so you really can't tweak the basic sound very much. IMHO, tube rolling allows you to make subtle changes to the amp's voicing that would not otherwise be possible.

Excellent post, Wasnex!

 

[MobileHolmes]

Nobody is really expecting divine favor by merely swapping a tube, despite the jokes alluding to this. However, even ignoring the artsy description of tonal qualities, it's hardly pseudo-science. It's actual science. There's documentation about the inherent frequency response, gain factors, geese man. Lots of differences. It's hardly changing a length of wire. Why is this so controversial?

View attachment 2925581

Man, those tubes are all about the scooped mids

 

[byacey]

So what you're indeed saying is that if we go ahead and remove one of the ways in which these tubes are inherently different, they become more the same, right? Isn't that how your statement reads? That if we make them the same artificially, that they become the same. Why bother saying that? What you're really saying is purely theoretical, and I can't help but notice that. It is also 100% fact, yes. If we build them all identically, and use them all in the same amp, and adjust the parameters identically, and use the same guitar and cab, play the same song, at the same time, then naturally they will all sound the same, presumably. Not only that, but someone would think something weird is going on.

Do you play guitar? If so, don't you notice the differences in sound from each tube? From each amp? Cab? Do you sample them? I'm speaking very objectively, here. I mean to exactly pinpoint that there is a difference between someone who can engineer, design, and build an amp, and someone really listening to tone quality and nuance. I'm NOT saying you lack one or the other. Not at all. I am indeed saying that there is a difference in the processes in both programs, and that a person built for one part (design, engineer) may not even care about the other (how it sounds).

Aren't you supposed to be telling me that V1 is the most critical, because that's the one with the biggest effect to the signal downstream?

You have a fairly impressive length of time with equipment, and I'm sure you put all that stuff in your signature to get someone to stroke your ego over it, and you're also trying to tell me that changing tubes will have very small, probably inaudible differences? Are you really trying to tell me that even with this graph showing subtle differences, that all tubes are almost identical? Granted, they follow an admittedly VERY SIMILAR curve, but NOT IDENTICAL. There's ONE difference. How do they sound? JUST LIKE WITH ANYTHING EVER MADE EVER, EVER, they aren't identical. Some may have been built by folks hung over on Monday morning, whilst others fail the QC standards.

Why so many different brands? Even if only a few manufacturers? Why do some amp manufacturers use exclusively one brand? Don't tell me it's all because of sponsorship and financial arrangements. There had to be a reason to begin negotiations in the first place. If a tube manufacturer made a million tubes for brand X amp builder, and they all sounded horrible (thereby proving that there are differences), brand X probably wouldn't care if they were offered at discount. Brand X would likely choose consistent and similar tubes that made their amps sound great, right? From one manufacturer. Because who knows how the others sound, bringing it right back around that each one can be subtly different. They're like tract homes, and every one has subtle differences, right? Color, floor plan, I mean really.

That is all.

In listening tests it's important to maintain the same gain level. It's a verified fact that human beings always seem to favor the loudest sample as sounding best. Additionally, it's hard to remember accurately subtle nuances of what you heard 2 minutes previously, unless you have some method to A/B the samples very quickly. Something else to consider is what sounds better for one source may not sound as good using another source, ie. different instruments.

 

[GreyBeard]

I have an Ampeg V-4BH. As predicted, I am now going to exercise my right to go and change some perfectly fine, working, good parts, for no real reason.

I found a red-lettered "CHINA" preamp tube in this amp. Probably offers some great access to breakup, and all, but meh. I wannit out of there. I went to "Amplifiedparts.com" and ordered a full preamp tube set for this thing (which the owners manual incorrectly states BTW, 3x 12AX7's and 1x 12AU7 is correct).

The inevitable question arises: is there a "preheat" time? Any "break in" period for preamp tubes? I've heard some high-end radio amp guys (using the same 12AX7s) talk about a sudden change in sound, usually for the better, but a change none the less. I know that biasing is for power tubes only, but these have unique needs also, right? After I change these tubes, magic should flow from the bass while it's just hanging there hands free, right? These will be what makes the "extremely average" player into a bass hero, right? Like saving orphan children from a burning hospital with my guitar type of awesome, right? Just wondering.

I had a Traynor YBA200 that I played around with the preamp tubes a bit. It can be fun but, you'll have to really strain you ears to detect much difference. But, what the heck? It is your time and money and if you enjoy doing this sort of thing, have at it.