I built this for a friend who plays in a lot of ridiculous drop tunings (down two+ steps . It's a high gain SE KT88 build crammed into a chassis fit for a Fender Champ. It has an interesting voicing (closer to a bass amp) and a LOT of gain but is rock stable and cleans up well with just the volume knob. It's based off of the same topology that I've been playing with for a while and gets a great full distortion by using a balanced mix of preamp and power amp distortion. Haven't tried it with EL34's yet, the KT88 sounds too frickin great! I'll try to record some sound clips before I ship it off.
I used a goofy mix of turret, tag and PTP construction which worked out quite well, after much planning. Each gain stage ground is fed right back into the respective decoupling cap and the only place the ground touches chassis is where the speaker output meets the transformer ground (this in turn goes straight to the first decoupling cap ground). The amp is dead quiet with the volume maxed and a set of humbuckers (single coils of course buzzed like mad).
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I built an amp something along the lines of your amp. i called the Beast, it is SE, and runs many of the octal tubes 6v6,6L6 EL34 6550,Etc..
Its something like a Marshalized champ,but with beefed up transformers.
Also built a 2 channel version Beast II it uses a 5879 channel,and a 12AX7 channel. Also the output is dual octals,with an option of just running 1. A few people have built the single version.
I think Mark Huss has the schem somewhere on his site or info about it. He made some clips of the beast he built. And with any circut,you can voice it a little different with small tweaks. I think these clips are useing a 6L6.
the DD is a drop D thing.
But i like the SE stuff. Also really like octal preamp tubes. They sound so sweet.
Cool build Cliff, what xformers did you use ? I have been thinking of building an SE thing designed to squeeze the most out of the new KT120.
I came across Mark's Beast clips on SEwatt a year or so ago and thought it rocked but had no idea what it was. Mark was kind enough to send me the schematic, posted below. It was designed by Richie Hall(Plexi) of 18W fame ( It just dawned on me that that's you Richie ? ).
I had the idea to make a Beast with 2 switchable out put tubes so you could A/B 2 tubes at a time that I was gonna call the 2 headed Beast - thought I had an original idea for once, o well.
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The OT is the 20W one from Musical Power Supplies (about $40 shipped) and the PT is the 750VCT@150mA guy from Allied ($50 shipped). The PT puts out a hefty 530V after the rectifiers, but I wouldn't throw a KT120 at this design. You'll need to go a bit bigger on the transformers to really get everything out of a tube that big.
I love the line filters too. They automatically ground the third lug when you screw them down and they are high quality (made in Japan). It's also nice cutting out a square hole as opposed to the goofy standard IEC shape. I've got at least a couple dozen of them (at least) and will offer them up for sale/trade when I sort through my parts and get everything more organized.
The guts have changed a bit from what I posted above. That was what I had built for the first fire-up and it had a few mistakes. All of the controls were also wired backwards (oops!) and the channel switch didn't work right (flipped two nodes). The On-Standby-Off switch was also wired wrong on the standby part. I fixed all of this last night, added in a bit more gain, bypassed the power stage cathode (1000uF 50V) and am waiting for my girlfriend to wake up so I can test everything!
Sounds pretty cool.
I wish I had a bunch of spare parts to build something like that.
I had to canabalize my 6V6 Rocket for an amp repair I did for a guy.
I forgot to order a switch and cap can bracket so I had to rob those.
I need to replace those parts because that little Rocket is fun to play with.
I came across Mark's Beast clips on SEwatt a year or so ago and thought it rocked but had no idea what it was. Mark was kind enough to send me the schematic, posted below. It was designed by Richie Hall(Plexi) of 18W fame ( It just dawned on me that that's you Richie ? ).
I had the idea to make a Beast with 2 switchable out put tubes so you could A/B 2 tubes at a time that I was gonna call the 2 headed Beast - thought I had an original idea for once, o well.
Sounds great to me. I'm probably more infamous than famous
The KT120 tube is something i was wanting to get to try in a build. Sounds like a great tube.
The OT i used for the Beast II was a 35 watt SE heyboer.
The amp is sounding great after a bit of tweaking. The dirty channel is crunchy and full while the clean channel sounds like a deeply voiced Fender. I like it a lot, but there is quite a bit of hiss in the dirty channel because of the nature of the "wide open" design I used. The amp is stable but has a lot of gain so I'm debating on whether I want to strap the plate resistor with caps to limit the high end response or leave the amp as is. Is there an acceptable cap value that can cut down on has without neutering this amp? Are there any other tricks I can use to reduce the hiss without neutering the amp?
Usually plates are bypassed with 100pF - 1nF but it depends on the stage, whats feeding it, whats after, you know.
In the few high gain amps I have built I find when running wide open you get a lot of the "picky" highs. My lasted amp, had two cascaded stages, second stage had a 2.2nF bypassing the plate load.
I'm thinking that the cathode follower after the first two gain stages that buffers the TMB tonestack is allowing this amp to be a lot brighter than with just a gain stage driving a tonestack. The much lower output impedance means that I get a lot less attenuation on the highs. Would reducing the cathode resistor in the cathode reduce the frequency response? I know it clips harder, and asymmetrically at that, but too much even harmonic in the preamp sounds blatty in my experience. Perhaps I'll try the capacitors first.
If you don't like the way a snubber cap sounds, you could always try dialing down the gain a bit by either : subbing a lower mU tube in the first stage, or putting a trimmer in ala Dumble to control the signal fed into the distorting stage, or using a split load plate resistor in the first stage like some do to tame wrecks : http://www.blueguitar.org/new/articles/ ... 010629.pdf.
Lowering the gain was the first thing I did. I may drop the last stage down just a bit more, my current setup is 100k plate and 4.7k cathode which overall gives me a gain of 54000ish. I didn't bypass the first two stage preamp cathodes initially and after tacking those in, the sound improved but the gain jumped up a bit. I may drop the last stage cathode resistor down to 10k to tame things down. I kinda wish I would have put a master volume on this as well and I may stick one in if my friend wants one.
It definitely doesn't sound bad with the first two stages strapped with 1000 pF caps but it's still quite noisy. I'm already cutting down around 4000 Hz with the 1000pF caps and I'm afraid if I go much bigger in value it'll tame the amp too much. I'll leave these in for now, drop the gain and see how it sounds.
Cliff, you may remember I build a SE KT88 earlier this year. I had great success with adding a conjuntive filter on the OT. I put in a toggle to control this, and I switch it in for high-gain leads.
Yeah I saw the SEL schematic after I finished most of this amp and wanted to see how others implement a master volume on a SE amp. I was going to work out a method for a failsafe master volume but but I've got enough good quality pots to not worry about this.
I noticed that the SEL uses a 430 Ohm cathode resistor on the power stage. I calculated the same value with a 3k output transformer and a much heftier 530V b+. I actually put in a 22k/68k voltage divide in the b+ after the first stage to guarantee that the 450V caps never see past 400V with no tubes installed. This has the added bonus of draining the b+ caps quickly and drops the screen and preamp voltages for more distortion. I was going to replace the caps with ones of a higher voltage rating but the voltage divider trick worked well. Now I get to try to blow up my new build at practice .
. It's a high gain SE KT88 build crammed into a chassis fit for a Fender Champ. It has an interesting voicing (closer to a bass amp) and a LOT of gain but is rock stable and cleans up well with just the volume knob. It's based off of the same topology that I've been playing with for a while and gets a great full distortion by using a balanced mix of preamp and power amp distortion. Haven't tried it with EL34's yet, the KT88 sounds too frickin great! I'll try to record some sound clips before I ship it off.
I'm probably more infamous than famous 
.