Class A Trainwreck?

[mtheory]

You were the one that wrote the opening post.

I've already explained that, more than once.

You need better books -

Any suggestions? I've heard that the Dave Funk book is very good, but it appears to be out of print.

and you might consider changing your moniker, "Mister Theory".

You started right off by talking down to me and treating me like a moron, for commiting the "crime" of using the term "Class A" in a title in which the term may or may not become relevant.

I feel that I've fully clarified myself and have even apologized for my ignorance. Yet, you still couldn't resist the urge to disrespect me yet again, by mocking my moniker. Really classy.

Next time, try being a little nicer.

Pot, meet kettle. Rather than assuming that I'm so utterly stupid that I've fallen for some infantile marketing gimmick, you might've actually read what I'd written, and responded to my question. Instead, you decided that I needed to be talked down to, as "punishment for my stupidity."

Just like others, I don't tend to respond favorably when I feel as though I've been disrespected, as I have been once again. You MIGHT be the most brilliant tube amp engineer that the world has ever seen, but you don't do so well at communication and treating others as you'd like to be treated, imo.

Am I over-reacting? Possibly. But, twice in this one thread, you've made disrespectful comments directly to me. The first one, I took responsibilty for, because I made the egregious error of mentioning the term "Class A" without knowing the clinical definition.

You've gone out of your way on this second one, however, even after I'd fully clarified myself. Perhaps you like to be treated like this by those that you wish to learn from, but I don't. Respect is earned, not assumed.

G'luck with your build

Thanks. It should be a great learning experience. It already has, in one sense.

[dartanion]

Everyone CHILLAX!!

Man alive, this place is starting to sound like...er, nevermind.

Since you have only built a couple of amps, I suggest trying to build an Express first, and then try building a customized version of it. FWIW, I think you need to get past your aversion to 6V6s as well. They all do not sound the same and they will sound different in different amps. I offer my Vapour amp in 18,20,30, and 35w versions. The difference in headroom in each amp is marginally different, they are all loud as hell, and they are all pretty crunchy even at lowish volume. Yes, the lower wattage versions have less headroom, but the way you work a Wreck is from your guitar. Set the amp up with the appropriate volume/crunchiness desired, then roll your volume back on the guitar to get your cleans. The 20w Vapour uses cathode biased 6V6s and it really sound deadly close to the 35w version with EL34s. Of course, I use nice NOS tubes in most builds, so that helps.

Anyway, do what you want, but first figure out exactly what you want and then chart a course for it.

[mtheory]

Since you have only built a couple of amps, I suggest trying to build an Express first, and then try building a customized version of it.

I've gone back and forth on this more times than I can count. It probably would make at least some sense, wouldn't it?

FWIW, I think you need to get past your aversion to 6V6s as well.

I REALLY wish I could, but I've not heard a single 6v6 paired amp that does it for me. They all tend to sound a bit too squishy/compressed and "constipated," compared to my beloved el34s.

Set the amp up with the appropriate volume/crunchiness desired, then roll your volume back on the guitar to get your cleans.

Is there any other way?

Anyway, do what you want, but first figure out exactly what you want and then chart a course for it.

Well, I THOUGHT I was doing this, but now you've got me leaning towards full Express clone yet again!

Speaking of which, a buddy of mine had an original in his store for a while (it eventually sold for a stupid amount of money, back to the original owner, no less). He owns, or has owned just about every piece of "God tone" gear ever sold, and he flat out did not like this amp. Is there any reason to believe that there could've possibly been an original TW made that wasn't breathtaking?

[dartanion]

To each their own right. One man's trash is another man's treasure.

I think some players just don't bond right away with a Wreck style amp, even the originals. They can be unrelenting and if you are not up to the task to make her work for you, then it will expose you for your weaknesses. As well, you never know what has been done to a particular amp, so it may have been tubed wrong, may have been modded, may have needed servicing. You just don't know.

For you, I think you should build an Express as a baseline and then think about a custom version. You may even like the Express enough to not chase the custom version, but hey, it'd be a great learning experience. As well, you could always mod the Express to a lower output version. One big reason to build an Express first is that they are a tricky build and can drive even experienced builders crazy because of their inherent razors edge of stability. Also, it was already mentioned, but you are asking for problems if you leave off the NFB. Having NFB is necessary to keep a Wreck stable. You'd have to lower to gain significantly in other ways for no NFB to work for you.

Things to consider for the Express build. If you get a Toneslut or Pacific PT, there are 300V and 260V HT taps, so you could add a high power/low power switch that allows you to use both sets of taps. Essentially this just lowers your B+ voltage, which in turn lowers the output. This is exactly the same thing that a VVR does for you, although the VVR gives you everything between full B+ down to whatever you have the limiter resistor value at (most are set to ~10-20% output). However, adding the VVR may be a bit too much too fast. Get the Express built, then consider your options.

All the resources needed are here, so start reading and downloading.

[mtheory]

They can be unrelenting and if you are not up to the task to make her work for you, then it will expose you for your weaknesses. As well, you never know what has been done to a particular amp, so it may have been tubed wrong, may have been modded, may have needed servicing. You just don't know.

I suspect something wasn't right with the amp. It had been serviced, though I don't know about any potential modding that may have been done, nor what it had for tubes. All I know is that he was very unimpressed, and this guy is the biggest tone/gear hound I've ever known.

there are 300V and 260V HT taps, so you could add a high power/low power switch that allows you to use both sets of taps. Essentially this just lowers your B+ voltage, which in turn lowers the output.

Wouldn't this change the bias drastically?

However, adding the VVR may be a bit too much too fast.

I've installed this on another amp of mine, but took it out because I really didn't have a use for it on that amp.

I do see your point about just building the real deal. There is some valid logic behind doing that first. I COULD certainly put a VVR on it to tame it down a bit, even though that's not a personal preference of mine. It does seem capable of managing volumes without seriously degrading tone, at least not until you reach WAY down, which I wouldn't have a need to do with this.

I thought that losing the negative feedback might cause some issues, and that assumption seems confirmed, on paper at least.

All the resources needed are here, so start reading and downloading.

Already there! Thanks again.

[Zippy]

They can be unrelenting and if you are not up to the task to make her work for you, then it will expose you for your weaknesses. As well, you never know what has been done to a particular amp, so it may have been tubed wrong, may have been modded, may have needed servicing. You just don't know.

I suspect something wasn't right with the amp. It had been serviced, though I don't know about any potential modding that may have been done, nor what it had for tubes. All I know is that he was very unimpressed, and this guy is the biggest tone/gear hound I've ever known.

Given how sensitive an amp these can be, if the person setting up wasn't into it, they may not have given it the attention it needed for peak performance.

there are 300V and 260V HT taps, so you could add a high power/low power switch that allows you to use both sets of taps. Essentially this just lowers your B+ voltage, which in turn lowers the output.

Wouldn't this change the bias drastically?

What is "drastic"? If you are interested in chasing this, consider adding a pair of bias monitor jacks on the back panel and an external bias control (either ala Komet or Fender). Flip the PT switch, adjust bias, and go. Unless you take the time to tweak the cathode resistors in a cathode-bias configuration, you'll have a good approximation at best. Better to go with switchable PT secondaries and adjustable fixed bias to hit the sweet spot. I've even gone this route on my favorite Tweed Super "clone" - allows me to run 6V6, 6L6, or (my fav') KT66.

P.S. Do you have an Air Brake yet?

[dartanion]

An Airbrake is one solution, however they suck tone after the first couple clicks in a big way. The VVR is a great solution, however it has it's limits too. The limits of the VVR is more about how far do you want to place your lower boundary of B+ if you are scaling the whole amp. At the very lower limits, around the 10% mark, tone also degrades. I find that setting the lower limit around 20-40 full B+ keeps it sounding great throughout the sweep of the pot and eliminates the need for the extra caps and such needed for 10% operation.

Ask around here and there's a lot of support for the VVR. It's a great solution both in design and execution. If you want an attenuator, the Airbrake is one of best types, so you can't go wrong there. There's a DIY thread here for them if you want to build your own.

[Zippy]

Would you agree, Dartanion, that an AirBrake will take the Express to the "25W" range and conserve tone?

[dartanion]

Would you agree, Dartanion, that an AirBrake will take the Express to the "25W" range and conserve tone?

An Airbrake can do that, but really, the difference between 25W and 35W is splitting hairs. My big issue with attenuators is that you start eating output tubes pretty quickly. I've toasted some very nice NOS tubes using various attenuators. This alone favors using VVR or other power scaling schemes in my mind. Again, the Airbrake is one of the best for attenuators, unlike some that I've used or seen. There's a popular one now that consists of a big resistive load then reamps the signal through a small SS amp for the output. It's funny how I've heard this device described as "transparent".

Anyway, if you go the Airbrake route, build your own as it's pretty inexpensive. But also try a VVR too. Dana sells complete boards, kits, or you can home brew it from parts and some G10.

[paulster]

Would you agree, Dartanion, that an AirBrake will take the Express to the "25W" range and conserve tone?

That's a 1.5dB reduction in power so it would be scarcely audible, particularly in a band context.

[mtheory]

Given how sensitive an amp these can be, if the person setting up wasn't into it, they may not have given it the attention it needed for peak performance.

That seems entirely possible. The shop is a very well-known booteekey builder, but brought the amp back to the store saying "Here's your $40,000 Bassman back." Probably safe to say that they didn't fully understand TW.

What is "drastic"?

"Drastic," as in bias can be spot on for EL34s but not so spot on for 6v6. i can't imagine how just plopping a set of 6v6s into the amp, if it's set up for EL34s, is going to yield optimum performance from the 6v6s.

Regardless, 6v6 just doesn't do much for me, personally, so it's moot.

No airbrake. I use a hotplate with my 50 watt amp. I was seriously hoping to not have to use anything external with this build, which is why I was aiming for 25 watts at the start of this thread.

In giving it more thought, and with Dart's comments, I can see where scaling an Express down to 25 watts by redesigning the output section might not be such a wise or easy task.

I've got a complete VVR board that I'm not currently using, so if I opt to go that route, I'm set. Frankly, with the brief amount I used that on a different amp, and in comparison to outboard attenuators, I'd much prefer to go VVR, if needed. I was real impressed with how it could bring volume down rather significantly before molesting the tone, and there is the added benefit of longer tube life that's worth considering as well.

That's a 1.5dB reduction in power so it would be scarcely audible, particularly in a band context.

I would expect the difference in headroom to be fairly significant, though.

[mtheory]

Not to re-open an ugly can of tapeworms (watched "Monsters within me" last night...fricking gross beyond words, man), but I have a question regarding Class A, as it pertains to one of my amps.

I have a 2xEL84 build that hovers dangerously close to Class A, based upon current draw. The draw is nearly identical from idle to full throttle.

Now, since the technical definition of Class A appears to be "an amp that conducts current throughout 360 degrees of cycle," but Class AB conducts for 180-200 degrees, what do you call an amp that conducts for a guesstimated 340 degrees, or in other words, more than AB, but less than A? Is there a classification for that, or does it just get lumped into A or AB, even though it's really neither?

[paulster]

That's a 1.5dB reduction in power so it would be scarcely audible, particularly in a band context.

I would expect the difference in headroom to be fairly significant, though.

Er, approximately 1.5dB!!

Actually, one of the things that really makes an Express what it is, is the way that the preamp, PI and power amp stages all go into clipping over a small range of volume, giving that very quick transition from clean to scream with actually very little difference in the overall volume. It is also helped by the compression caused in the power supply from the screens back to the preamp by the choice of the 1K dropping resistor rather than a more typical choke.

If you were to leave things as they were and use a lower powered output stage you could end up upsetting the fine balance of the amp unless you also tweak the PI voltages and/or bias point to get the same overall distortion characteristics. You also want to get the power supply compression to behave the same, which would be dependent on the current drawn by the power tubes so this is likely to require some tweaking too.

I'm not saying you shouldn't do this and, in fact, everyone should be encouraged to experiment with designs, but the Express is already pretty well honed, and it's probably easier to take backward rather than forward steps with it.

I would probably start with a vanilla Express and then tweak from there, when you can actually hear the effect of your changes and see how they change the feel of the amp, so you've got a good reference point. Or you could just use VVR since you're only talking about dropping it down by perhaps 3dB at the most.

I'm not a fan of 6V6 tubes in these at all. I've got some really nice sets of 6V6 tubes but every time I've tried one of them I've very quickly gone back to the Siemens EL34s. They just work in this amp.

Good luck with the project!

Paul