Twisted Express - Reverse Image Build with a Twist

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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RJ Guitars
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Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

If you've seen my "For Sale" blurb you are aware that somehow the machine shop I was working with to fabricate some Traditional Wreck chassis, made an error. They laser cut the holes and proceeded to fold the wings backwards. This created a really nice reverse image chassis. They ultimately recreated the chassis appropriately and I also bought the wrong way chassis for half price and figured I could sell them off cheap... not a chance. With the exception of the Rocket versions I can't hardly give them away. So I've been pondering what to do with them??

I guess everybody including myself thought that building a reverse image Wreck is not all that interesting even if it's cheap. One one obvious thing is that they are begging to be combo chassis... but a Wreck high gain circuit in a combo amp is sorta asking for trouble. Whatever I build, I'm going to make it in a head form first and build it in reverse image.

So hang on, I have an idea, some reject parts that nobody seems to want, and I've got a little time on my hands. The Twisted Express build is gonna be fun and I think I have something in mind that will be interesting and useful... And FWIW - I'll make it worth your while if anybody wants to build one for themselves??
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joeboo88
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Re: Re: Twisted Express - Reverse Image Build with a Twist

Post by joeboo88 »

I'll Try Bob, I would like to help...send you a PM?
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Re: Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

Hey Joe... (sounds like I might have a song there... you've probably heard that a few times?)

Thanks, This is mostly for amusement so no pressure and for sure no panic... things are what they are and an unloved box of amp parts is just another opportunity to explore.

I was able to work up the chassis and mount the transformers and all looks great. Since the amp is already out of alignment with tradition I went ahead and added the improved power entry socket.

I have a box of Heyboer PT's that are 120/240V that I had been saving for orders headed over to the other side of the pond. However, that market has sorta slowed down and I actually prefer the Edcor transformers for exports so these were another item that were on the "Homeless" bin.

I also have a lot of inventory in the Pacific - Wreck spec OT's, with an added 5.2K tap. Great sounding trannies and these are ideal for an experimental Express build.

In this build I amp going to deviate from the pure Express because I want to have just a little less gain and see if I can make something that is slightly warmer and combo friendly... but not quite as well behaved as a Rocket or Rockster build. Stay tuned...
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joeboo88
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Re: Re: Twisted Express - Reverse Image Build with a Twist

Post by joeboo88 »

Hey Bob sounds good..... I thought for a moment you were going to say you were going to us a 5879 tube as well :D

Sounds like fun....
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Re: Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

I didn't say.... But you never know?
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Re: Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

I had a free afternoon so I got a little wiring done...

I was able to power it up and verify that the tube heaters all lit up... hopefully the schedule will allow me to make a little more progress tomorrow.
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Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

I enjoyed some solder fumes for breakfast this morning and built the PS board. I used a traditional Express PS board although I did not use it in the traditional way. I added the filter caps to the board which used up all the real estate I had on the board. On this build the big resistor and the bias pot will both be chassis mounted.
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Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

Added some parts for the power tubes, the 1K power resistor, and the bias control pot. Ready to mount the PS board now.
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boops
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Re: Twisted Express - Reverse Image Build with a Twist

Post by boops »

Whowww ,very nice built!!!
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Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

Thanks Boops!

I worked up the preamp board and installed it this morning... at this point it should be clear that I am not working with the traditional preamp circuit.

JoeBoo had it right when he mentioned the 5879 tube. That is what I'll use for the entry tube. Joe had a little insider info from based on another project I had just worked up: http://diyguitaramps.prophpbb.com/topic128.html I wanted to post this over here because there is a bigger community of TrainWreck builders here... or at least in the pre-malware days this was the mother-lode of info and gurus on Wrecks.

I'll repeat some of what I mentioned earlier:
I wanted to use up some inventory that was sorta stuck looking for a purpose - thus the reverse chassis. Because it is a reverse chassis it is really begging to become a combo style amp. I know a traditional Wreck can be problematic as a combo amp so I wanted to tame the gain a little but see if I could still retain some of the good stuff.

I am going to use the 5879 as the first tube and I see estimates of getting a range of gain out of these tubes from 70 to 180. This is more that one side of a 12AX7 triode but not near what the two halves put out cascaded. I really liked the sound of the 5879 in my previous experience with it so it is in there for tone... I am hopeful to add a little more fullness to my Express builds... we'll see.

The 2nd gain stage is going to be a parallel 12AX7 triode. Again maybe I can add some thickness to the sound and get just a tad more gain than half a 12AX7. The last little bit of gain will come out of the phase inverter - which is not much. So my prediction for this preamp is that it will will be less gainy but smoother and fuller sounding than a typical Express preamp. I have left the original specs for the phase inverter and power amp sections so that maybe I can retain some of the Express edge.

This will be one less gain stage and obviously less gain than the true Express circuit. Hopefully ideal for a combo amp.

If life is kind, I'll get going on the front panel here shortly... stay tuned.
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telentubes
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Re: Twisted Express - Reverse Image Build with a Twist

Post by telentubes »

Looks good rj
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Re: Twisted Express - Reverse Image Build with a Twist

Post by joeboo88 »

Yeah that looks great
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Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

I worked on this amp on and off all day... anybody who knows me is aware I seldom do anything in a hurry. However, i this case I worked this amp up pretty quick which resulted in a few mistakes. I missed a ground wire on my bias circuit and had a little confusion in wiring the 5879 to match up with my modified Express PCB board. It was a bit of a challenge because in order to wire this board I actually had to turn it upside down and put the components on what would normally be the bottom of the board. I wouldn't do it that way twice but I really wanted to get this first prototype worked up with stuff I already had here. Once I got past those fab issues it sounded really nice, even with my Russian 6C3C starter tubes in the output section.

It's a little early to say but the preamp seems to have that extra fullness in tone that I was hoping for. I'll know a bit more once I can start voicing the amp. Because it was a little late in the evening and the venue wasn't right for me to open it up and play I used my airbrake to hear what it sounded like cranked. I was initially worried about not having enough gain but if anything I may need to dial it down just a tad... I'll need some more time with it to sort it all out.

I do have a little travel coming up so this is all I get done on it for a while.
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joeboo88
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Re: Twisted Express - Reverse Image Build with a Twist

Post by joeboo88 »

That's looks really good. I'm glad it turned out how you envisioned it.

And sorry to blab about the 5879, I thought that's what you were doing, but I should have kept my mouth shut :D
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Re: Twisted Express - Reverse Image Build with a Twist

Post by RJ Guitars »

I added a built in resistive attenuator to this amp... works quite well and was pretty simple to implement. In my first few tests I can't really detect any heat coming off the resistors but I need to work it hard to know for sure.
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