Trainwreck - Amp Development Platform

[RJ Guitars]

Hey Folks,

I've been working on something here for years (literally), not at a steady rate but slowing forming ideas in my mind about how it would be most easy to study Wreck amps. This is my greatest deviation from the Trainwreck format yet, but entirely designed to study the various Wreck circuits in a modular fashion. I know the amps are intended as complete units with the layout as an integrated part, but electronically and theoretically I believe I can analyze each part of the amp as a module. I could be entirely wrong and this may not accomplish anything worthwhile at all... but I think it will be quite useful.

I've used a standard Wreck power transformer and separated off two B+ supplies that I can switch in between. I can either have the pure solid state rectifier circuit of the Express or the GZ-34 rectifier of the Rocket. I incorporated the switch in between the two B+ circuit into the standby switch.

It's far enough along that you might be able to get the main idea but maybe not too far that someone might be able to save me from myself?

rj

[xtian]

OMGsoCOOL! Too bad Bruce Egnater already took the "Tweaker" moniker. Get some fancy copperplate dress on that thing, like our new buddy Gerry, and we'll put this thing in the Smithsonian!

[RJ Guitars]

OMGsoCOOL! Too bad Bruce Egnater already took the "Tweaker" moniker. Get some fancy copperplate dress on that thing, like our new buddy Gerry, and we'll put this thing in the Smithsonian!

Hey I had "Rock-it" coined B4 Ceriatone had theirs, it's just a matter of not worth it to me, I am in it for the technology and if anybody gets rich, it's usually not the first guy or the smartest guy to think up something clever... How about "Tweeker" or "Tweaquer" or "2-weeker"... could have a lot of fun on our way to the cease and desist judgement dancing around their IP claims. In the end Bruce is probably a good guy and I wouldn't want to cause him grief...

[KellyBass]

That looks great, RJ! It'll be interesting to see what tones you discover. How about an extra socket...in the vicinity of V1...for a pentode?

We all had a good laugh, 'round these parts, when we saw the Egnator "tweaker" amp. In Oklahoma, the word "tweaker" carries with it some fairly negative connotations.

[xtian]

Oh, tweakers are ever-where. North of San Diego County was meth central for a while. Primus wrote a great song, "Damn Blue Collar Tweakers".

https://www.youtube.com/watch?v=M1C2SFrwdq0


Sorry, derailed for Primus:

https://www.youtube.com/watch?v=0mCY88iuzo0

[geetarpicker]

Primus is one of my favorites!

[RJ Guitars]

We had that name and were doing great here in our little home town... then these other guys showed up on the national scene and covered our name but they never really had our songs right...

Edit - didn't they spell it PRYMUS?

[RJ Guitars]

Made a little more progress on the amp... it might look a little more Trainwreckish now with some Vectorbord in there.

Since the preamp board is separated from the phase inverter, I can make a new preamp board with the EF86 or any other small or big change. Also, with a minimal number of changes I can change it into a Rocket or Liverpool and a few variants in between. Should make for fun!

[KellyBass]

That's a great song! I hadn't heard that one. I can remember hearing / seeing Claypool for the first time on the Dennis Miller show...maybe 1990? Around that time, I was in my bass playing prime and feelin' pretty cocky. Seeing him made me want to sell my rig and take up a hobby. I know!...amps!

I'm glad to hear you're keeping a spot in mind for a pentode, RJ. I've had some great luck with ef86 rockets. The distortion character, and the massive low end, is really something to hear. They seem very sensitive to slight voltage changes and coupling. I have no doubts that you'll find some cool tones!

[RCGPNY1]

RJ...just to play devil's advocate...please try a 5879...I would love a 5879 based preamp with a lerpoole style EL84 output stage....I believe the 5879
to be less problematical than ther EF86's...not quite as much gain perhaps
but that big tone and fantastic overdrive character. Just Vol, 6 pos tone switch and cut(maybe)

[RJ Guitars]

yeah, the idea was to create each stage as a module so I didn't have to build a new amp when some bright idea popped into my head. I started this about 5 years ago with a 325-0-325 laydown transformer. It was a big project with no driver except to build a handy test tool... so it sat and collected dust.

Recently I decided to have my old Stancor A-3801 output tranny cloned and wanted an amp where I could easily swap output trannies without changing anything else, then do some direct comparisons... So i dug out this modular amp and I replaced the power tranny with a Wreck PT. I hope to have it done when the Stancor OT clones arrive. I've got a lot of other things I want to study with the Wreck circuits and among other things I want to make up something I can use to do some tube matching.

[RJ Guitars]

I am not familiar with a 5879 tube... nor the ef86 really. I just know that Vox used them in some of their old amps and some folks really likem

[xtian]

Wow, RJ was in Primus before all the other guys were in Primus. That's really cool TAG trivia!

[RJ Guitars]

A build progress update. I have the output tranny installed and a bit more progress on the wiring. I wired up the power supply and added an analog volt meter on the front panel with a rotary switch that allows me to read the voltage at each node on the power rail.

I did hit a snag on the bias supply that has me a bit disappointed with some new filter caps that I tried. I usually test my voltages as soon as I have it finished up. That all went well until I measured the voltage on the bias supply. It only read a negative 8 volts.

I was sure I made a mistake either in design or execution... I created a PCB board with a bias supply that was schematically the same as an Express PS circuit. I also was using an external bias pot that was only 20K rather than the 25K pot in the typical Express amp. I swapped a couple resistors and did some voltage measurements before I finally became suspect of the filter caps. I made the cap swap to a set of NOS Sprague caps and viola - a negative 29 to 40 volts with no load on the supply.

For most Express bias supply packages I supply Mallory 10uF 100V caps according to the specs specified in the Express schematic. For this particular build I was using some new ITT 10uF 100V electrolytics that should have been correct for the job. This was the 2nd time I used caps from this same bag and the 2nd time I've had a failure. Does anyone have any experience with these or had similar failures in an Express bias supply? These were sent to me for testing and at this point I am going to suggest "just say no" to ITT caps.

Otherwise the amp is going well and I am pleased with the layout and look of things so far.

[RJ Guitars]

I took some time off from this project and all other things in life in order to devote some time toward my daughters wedding this past weekend - all went well...

I was finally able to unwind by spending some time out in the shop today and finish up my amp component test platform. It is all done... or at least at that stage where it is a functional amplifier with everything apparently wired up correctly. I used old preamp tubes, some inexpensive Russian power tubes. and an old 5U4B rectifier tube to test it out. I ultimately had to swap the leads on the output tranny to make an annoying squeal go away... it didn't squeal until I put EL-34's in it if anyone wants to explain that to me?

I used Heyboer vintage trannies and many of the parts that are standard in a traditional Express. The preamp board(s) are essentially the same layout as the traditional Wreck board. You can see the similarities as well as the deviations I made... but in the end it sounds and acts like an Express.

I eventually swapped out the tubes to use some old Dutch El-34's and a vintage Mullard GZ-34 for the alternative Rocket style power supply that is built into this amp. I've had a good run on Express builds this past couple years and each one seems like it sounds better than the previous one. In this case I wasn't sure what to expect since it's such a deviation from the standard build. It sounded very good... can't say it's the best one ever but having only played it 30 minutes I can say it could be a contender. This is good news since I want to use it to compare various components... I just received the new Mercury Magnetics Stancor A-3801 clone today. Project #1 for this build is to perform a thorough comparison of output transformers for Express builds.