mcrracer wrote:Actually my Rocket/EL34 SE did not work out at all for me. I built it with a switch for 3 different Cathode resistor values in order to use many different power tubes. I just could not get it to do any cleans hardly at all. I wasnt happy with it so I pulled it apart...
Ow!
I wish you had talked with us about that. Given the usual performance of that pre, we know that the cleans are there. I'm betting that a lil' padding before the output section would have tamed that easily. A quick way to empirically determine the correct value is to use a trim pot or "master volume" to find the sweet spot and then hardwire it.
RJ has at least one Project Amp with trim pots in abundance to let him tweak the various stages.
Please let us know when you are ready to try it again.
Hey Zippy , Thanks. I know that it had to be in there given the performance of the Express SE amp I built. I was just kind of impatient to get to my PP projects on my plans. I guess my immediate relative success with the Express Se spoiled me.I will get back to it. The DLM bug has bitten me. There is an allure to getting that kind of volume and tone out of one power tube. The parallel tubes interest me too but that is going to get expensive quickly due to the iron necessary to pull it off properly. I am on a budget that kind of keeps my addiction, ahem , my hobby in check.
It is just like that Swamp thing amp I was building somthing was wrong from the start and I figured out the layout of the board is a mirror image so now I went into visio and doing a complete layout. These problems put me off wanting to complete that amp.
Another "EAR OPENING" experience. I took my Express / KT88 to a Blues gig of a friend of my brothers last night. I set it up before they started and before the customers started coming in. The leader of the band hooked up with a Les Paul and he sounded OK. He is a showman not necessarily a great guitar player. He liked the amp. He normally plays a Fender tweed, I did not look at it closely. The other guitar player then asked me if he could play thru it. Sure. He plugged in his Strat. And all hell broke loose. At first he just noodled around a little. I explained the controls , left the boost off and set the gain and master vol at about 12:00. I explained to him about rolling off a little vol on his axe to control it. He played one Blues tune , then the bass player came in and he started in . My brother sat in on drums as their drummer was not there yet. The more the guitar player played the more comfortable he got with it. By the 2nd set he had figured out enough that everyone was commenting on this little bitty amp on a ten inch speaker. He had it screaming, wailing and sustaining notes like no tomorrow. By the end of the night he had her figured out to the point he broke out in Santana's Black Magic Women From the beginning to the end of the song including the intro. This is where the amp and the Strat player became one. He used the sustain and feedback of the amp to almost exactly replicate that song. As a bass player I have played it numerous times over the years but never heard it played like that. The clarity was unreal This amp in the right guys' hands is like an artist and his paint brushes. I should mention that this guy normally plays thru a Peavey SS amp. I was surprised he picked up on the nuances of a tube amp so quickly. The other guitarist was playing thru his amp and the differences were painfully obvious. Even the bar owner came over to me and asked"what's in that thing?" The other guitar players that were there came up to me and started asking questions. I now am beginning to understand the mystique around the whole Trainwreck thing. I hereby request permission to join the others in paying homage to Ken and his creations. I am starting a Rocket /Rockster PP build with either KT66 or EL34, not trying to improve on Ken's design but to expand upon them. I am in no way abandoning my DLM search. I have one circuit I know works well. It may not be what Ken built or even had in mind but I still thank him for the inspiration to even attempt a big bottle SE amp. I like the Express pre on a KT88 power amp and look forward to firing up my next "Ken inspired" amp.
Sorry forgot to mention that. It is a Eminence Legend ten. I forgot the exact model and don't see it on the speaker. It is in an semi open back cab which I designed and built out of 1/2" plywood covered in maroon carpet. I will see if I can post a picture.
tweedeluxe wrote:mcrracer - are you willing to share any more info about your SE express? I am mostly curious about how you set up the output stage and if you kept half of the PI- circuit. Any NFB?
I'm about to start a high-gain SE KT90 build and am looking for a good starting point. Thanks.
My production amp, the Absinthe, is a parallel EL34 SE wreck type affair that retains the PI circuit. Works great really and is a simple thing to do. Just make sure you feed the power amp from the appropriate side of the PI or it'll squeal really bad.
I need to come to Redwood City and see what you hath wrought Dartanion. Ron Worley heard your amps at the NY Amp fest and spoke
glowingly of your results. The one he absolutely loved had a different
name because I would have remembered Absinthe. Do you need to pour
a little cold water on these? LOL.
Lemme know if an audition is do-able in the near future and best wishes
on your endeavor,
Noel Grassy.
All excellent things are as difficult as they are rare__B Spinoza
I now have a shop in Mountain View where I build everything except the custom hardwood cabs. Those I do at my woodshop in my garage.
The Vapour 30 is the one that everyone was raving about. This is my take on the Liverpool, which I have taken quite a few liberties with regarding parts and layout. I will have another few of these completed in a few weeks along with some other amps, so I'll let you know when a good time to come by would be.
mcrracer wrote:I took an Express pre up to an including the .022 coupling cap off the second 12AX7 tube. I took that into a 1Meg Master vol into a 5.6k into pin 5 of the KT88. I think I used a 1000uf cathode bypass cap and a 300 ohn 5 watt resistor. Fed b+2 through a 1k 2watt resistor to pin 4
To make it more like a SE version of the express, would you need to add an extra gain stage for the PI gain, NFB and fixed bias?
Or you can leave the whole PI circuit in place and feed the power amp from one side of the PI. Pick the appropriate side or your NFB will be PFB = HUUUMMMMMMMMMSSSSQQQUUUEEEAAALLLLLHHHHHUUMMMM........
This way the PI does it's thing without having to approximate how it would be have using a single triode. If you are trying to be economical, then go for the approximation as you save yourself a tube.
Tyru - I'm planning to use the same single triode faux-PI in my upcoming SE build. Take half of either a LTP or half a cathodyne, you get the same result.
If the amp is a little harsh sounding, consider a small (<100pF) cap across Rp of the fake-PI. It still won't quite approximate the ~50pf across the PI plates in a TW design though - so that there may be a reason to use two triodes.
Dart, if I may ask - is the Absinthe cathode biased?
Is there any more work on the Rocket-SE concept or is it dead?
I'd love to shoehorn a "Pocket Rocket" into my Vox Pathfinder cabinet. Mid-gain grind, clean chime, and taking a good fuzz pedal are my priorities, and I love the Top-Boost vibe, so the Rocket is my pre. If the clean chime benefits aren't there without the PI and P-P output, though, I'm guessing it'd be one of those 50 gallons of **** in a 30 gallon bucket things to fit inside.
