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|2/3/2001 9:38 AM|
||Possible origin of Trainwreck preamp|
Ever since somebody here pointed this out to me I'd been planning to make some drawings that illustrate graphically how the Express preamp evolved from the humble Princeton Reverb. Well, here they are:
With the PR using a cathodyne PI, the Express drawing I chose to use was an early incarnation of my Blues Express that was originally based on the Wreck clones from Cxxxxxxm... reportedly similar to a real Wreck on paper but without the legendary tone and response.
The posts from aron and wreckboy about the Dirty Little Monster (an early prototype amp from Ken Fischer) offer some corroboration to this "theory of evolution". Jumper out the 3M3/10pF reverb splitter on the PR, change a few values between the 2nd and 3rd stage, tweak the tone stack and you are practically there.
The 3rd stage in the PR is like a pre-driver for the cathodyne PI which adds no gain to the signal. (Many amps with a cathodyne PI will use such a pre-driver stage to boost the signal.) However by running the 3rd stage into the LTP PI used in the Wrecks, you increase the gain factor considerably. I think that he upped the value of the cathode resistor from 1k5 to 10k to get a smoother distortion sound; cathode biasing the EL84 output tubes of the DLM would also smooth out the sound a bit.
In any case, I believe that comparing the Princeton Reverb schematic to the later schematics of the Cxxxxxxm clones gives us some insight into the genius of Ken Fischer.
P.S. The first drawing also shows how the John Stokes power supply mod for the PR would increase the voltage going to the PI by moving the wire from the ~240vdc tap to the ~320vac tap. YMMV!
|2/3/2001 10:37 AM|
|John Kelley Brown|
Thanks for the insight. Interesting.
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|2/3/2001 3:24 PM|
Steve, not to take away from your research, but the Dirty Little Monster is a more recent project, some 15 years younger than the Express. It is a completely different circuit. It doesn't use EL84s either. Hogy
|2/3/2001 5:37 PM|
Do you think that Ken might have recycled the name "Dirty Little Monster"? The posts here from aron and wreckboy indicate that the DLM was a prototype built before the Liverpool:
The following was in the Open Forum last Spring so it is not available as an archive yet, but here is the post I saved from "wreckboy":
Ken can build a "Trainwreck" amp just using spare parts that he had laying around his shop (the same parts any tech would have). I own the first Trainwreck amp built. It's a 15 watt Class-A amp built on a gutted Fender chassis. No aluminum chassis, no custom transformers, parts from old Ampeg/ Marshall/Fender amp, using a stripped Fender circuitboard.
He calls it a piece of "junk" made from "spare parts" that "blows away any AC-15 or Marshall 18 watter" ( and he has worked on and played a number of these classics). It was built to test out ideas (ex. it had features like switchable fixed/cathode bias ) before he built the full power (4 EL-84) model. Ken does have the "Magic Touch" but he also has the "Magic Ear" to go along with it. It looks like just another Fender chassis that someone had modded.....but when you hear it ....Wow, it's like from another world.
Hey, next time that Aron comes back home I'll let him play the the amp and he can do a review for Ampage
Now wreckboy doesn't actually say that the DLM used two EL84's but I assumed that from the 6th sentence. But you know what they say about "assumed": it makes an ass of u and med!
|2/3/2001 6:01 PM|
In one of Gerald Weber's books in the Trainwreck section, Ken talks vaguely concerning the evolution of his amp line. He said he made a 15 watt cathode biased Liverpool protoype first for a friend using some spare parts before adding the other two EL-84's to become the Liverpool as it is today. He later says that he tweaked out the Liverpool by making it fixed biased and using 6V6's or EL-34's to become the Express amp. However, I'm sure that those two changes are not the only differences between the Liverpool and Express, but perhaps they are more similar than we realize. Take care,
|2/3/2001 8:14 PM|
Steve, the DLM aron played was indeed a prototype, but a recent one for a project that hasn't been realized yet. The "junk parts amp" wreckboy owns is the 2 EL84 prototype of the Liverpool. These two have nothing in common, it's just a simple mix up. Hogy
|2/3/2001 8:35 PM|
Thanks for clearing that up! In rereading the posts from aron and wreckboy I see that they were talking about two different KF prototypes:
DLM: It looked like a typical Train Wreck amp but with labels for the knobs.
I collected all of the posts I could find on these two prototypes in this file:
So is there any chance that Komet will be producing the Dirty Little Monsters? Aron mentioned that it was an 8 watt amp... is that true? Can you tell us what output tube(s) it uses?
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