Can I Wreck It?

[Weathered]

So, I've attempted to build a Ceriatone 50W Plexi twice now, with the same result (not a good one). I've gotten to the point where I want to try something different, so I've thought about trying to build a TW Express into the chassis. The chassis has the big cutout for the PT, and 2 cap can spots. In looking at the Express schematic, it uses 3 40uf caps and 3 20 uf. I figure that I could actually get away with a 50/50 can in one spot and a 40/20/20/20 in the other and not need any caps on the board, which would make it an easier build from the execution standpoint.

The only issue I can think of is that the PT I'm using is more than a bit hot (720v versus the 585v listed on the schematic), which might be a bit too much.

Any reason this would fail? Apart from my own ineptitude?

[roberto]

If you have failed twice to build an amp with a certain layout and with many people that can help you, I suggest you not to go to a project with a custom layout and so on, but to keep on the marshall project.

When the amp will sound ok, then go to the custom one.

[M Fowler]

So, I've attempted to build a Ceriatone 50W Plexi twice now, with the same result (not a good one). I've gotten to the point where I want to try something different, so I've thought about trying to build a TW Express into the chassis. The chassis has the big cutout for the PT, and 2 cap can spots. In looking at the Express schematic, it uses 3 40uf caps and 3 20 uf. I figure that I could actually get away with a 50/50 can in one spot and a 40/20/20/20 in the other and not need any caps on the board, which would make it an easier build from the execution standpoint.

The only issue I can think of is that the PT I'm using is more than a bit hot (720v versus the 585v listed on the schematic), which might be a bit too much.

Any reason this would fail? Apart from my own ineptitude?

Maybe you should pop in a pair of KT120 power tubes if you have 720 volts to work with.

If you can't get a Marshall Plexi to work your not going to get an unstable TW Express circuit to work just my opinion. Also, Express is 600vct with 6K6 OT.

Mark

[Colossal]

I agree with Roberto's point. What about the Plexi isn't working for you? Have you identified it? Is it just the sound you don't like or is the amp actually not working correctly?

Another point to consider is to what degree are you trying to achieve The Wreck? A spot on copy or just the same preamp values? The Wreck PT runs at 300-0-300 (intentionally) and the output transformer primary impedance in a Wreck is very different than that of a Plexi. This not only reduces the amp's overall power, but also works in concert with the amp's design to bring out the specific characteristics that make a Wreck a Wreck. It is not a matter of substituting values to make a Wreck.

A Wreck is far more than the sum of its parts.

EDIT: Mark you replied the same time I was typing.

[M Fowler]

Dave, I wish these guys would send their high powered transformers to me I need some in that voltage range for my KT120's.

Mark

[Weathered]

If you have failed twice to build an amp with a certain layout and with many people that can help you, I suggest you not to go to a project with a custom layout and so on, but to keep on the marshall project.

When the amp will sound ok, then go to the custom one.

I successfully finished a custom build less than a year ago, and I've got 4 complete builds under my belt, but the Ceriatone layout doesn't work with me for some reason - the board is really wide, which makes the whole layout really cramped. I'd prefer to just drop a set of turret strips in there and custom build something based on a wreck rather than fuss with a cramped layout that I'm not comfortable working in to be honest.

Maybe you should pop in a pair of KT120 power tubes if you have 720 volts to work with.

If you can't get a Marshall Plexi to work your not going to get an unstable TW Express circuit to work just my opinion. Also, Express is 600vct with 6K6 OT.

Mark

The PT is the standard issue Mojo 50W Marshall PT - it's 360-0-360, so I've been landing at about ~425v on the plates or so.

I agree with Roberto's point. What about the Plexi isn't working for you? Have you identified it? Is it just the sound you don't like or is the amp actually not working correctly?

Another point to consider is to what degree are you trying to achieve The Wreck? A spot on copy or just the same preamp values? The Wreck PT runs at 300-0-300 (intentionally) and the output transformer primary impedance in a Wreck is very different than that of a Plexi. This not only reduces the amp's overall power, but also works in concert with the amp's design to bring out the specific characteristics that make a Wreck a Wreck. It is not a matter of substituting values to make a Wreck.

A Wreck is far more than the sum of its parts.

EDIT: Mark you replied the same time I was typing.

I have yet to get the thing to make a sound apart from when checking voltages, which is odd since I've triple checked the wiring. It does pop when I'm checking plate voltage, so it would seem that the OT is OK.

I'd be OK approximating the Express tone in something a bit higher wattage if need-be, or I would look at the Komet stuff if that was a better fit for the PT, since it's a perfectly fine Heyboer. The OT is Weber that I got in a bunch of parts, so I'd be fine ditching that for a Triode or Heyboer OT.

[Phil_S]

I don't know much, but will speculate that such a big change in voltage will change the operating parameters of the amp. Even if you build the wreck circuit, it won't sound like a wreck, and it's probably a good idea to adjust the B+ ladder to supply the preamp tubes with a lower voltage than the stock Express ladder will end up supplying.

If you do a custom layout that doesn't work, I don't think that's a big deal as long as you use it as a laboratory learning experience. What have you go to lose? It's not like you are building it for a customer -- that's a whole other thing. If you build the Wreck, just try to be extra thoughtful about where you place tings because it is prone to instability.

[Colossal]

I'd be OK approximating the Express tone in something a bit higher wattage if need-be, or I would look at the Komet stuff if that was a better fit for the PT, since it's a perfectly fine Heyboer. The OT is Weber that I got in a bunch of parts, so I'd be fine ditching that for a Triode or Heyboer OT.

You'd probably be better off going the Komet route as the voltage is significantly higher and the OT primary impedance (for the K50) is much closer to a Plexi. The K50 is a very ballsy Plexi.

You might be able to approximate the Express tone with your current setup but you won't have the characteristic and highly specific qualities that make an Express and Express. The Express is specifically designed for power tube distortion to occur first. This starts with the primary impedance of the output transformer and works backwards. The primary is 6k6 which rotates the load line counterclockwise in favor of intentional non-linearity, increased harmonic content, as well as lower output. The Express is very much a system and when you analyze it as such, you will see that nothing was left to chance. That was Ken's genius.

With the Komet K50 design, you are pushing the tubes pretty hard and some guys that have built them (and the K60) have ended up with red plating power tubes (and it's easy to see why). But tone is tone and amps that are run at such extremes often sound fantastic because of it (e.g. Vox AC30) albeit sometimes at the cost of blown tubes, transformers, etc.

[Weathered]

With that said, could someone supply me with a Komet schematic via PM? Hearing that it's a ballsy Plexi, that sounds right up my alley, and it sounds like I've got the right parts.

[Colossal]

Hearing that it's a ballsy Plexi, that sounds right up my alley, and it sounds like I've got the right parts.

Listen for yourself!

http://www.youtube.com/watch?v=JgKPwtcey_s&feature=plcp
http://www.youtube.com/watch?v=vB76UqCYxgs&feature=plcp
http://www.youtube.com/watch?v=nKkFb5HQwxo