Something a bit different - Legend 6V6

[strelok]

So I recently saw a youtube video restoring an old Legend combo. I had totally forgotten about these things, supposedly the super lead 50 model was used by Billy Gibbons on the Eliminator album. Anyways I have one head shell and chassis left from the three that I built a while back, as well as some transformers. Been tossing various ideas around in my head as to what to do with it. While I was watching the video I decided to look up the schematic for it. They're hybrid amps, 3 12ax7's and a SS output. Interestingly enough the tube circuit turns out to be basically a 2203 pre-amp with a few simple changes/additions. Neon lights and 80's cheese start going off in my head at this point.

Some interesting notes about the circuit:

-They were smart enough to include the PI. They must have recognized how important it is to the sound, given that they only take one output. It drives an op-amp which makes up the final gain stage before hitting the output driver. When the lead mode is engaged the lead gain control is switched in parallel with its NFB resistor which of course adjusts the gain of the op-amp.
-There's a local NFB network around the PI since there's no tube output stage, to allow for a presence control.
-The "Gain Color" Knob is a two pole RC filter with the pot acting as the second R, I'm quite curious to see how this affects the sound.
-A pair of clipping diodes reverse biased at +/-12V respectively get switched into the circuit whenever the lead mode is engaged.
-A fuck ton of volume/gain controls. Color gain, Rhythm Drive, Preamp Volume, Lead Drive, Master Volume.

So here's what I plan to do with it. It already has a PI, so why not couple that to a pair of 6V6's and make a little 20W amp out of it. I'm going for total 80's cheese with this, think Sharp Dressed Man/Danger Zone/Push it to the Limit type tone, so it should be a fun experiment. I'll be building it up on terminal strips, so it'll be easy to change to something more conventional if I don't like it / the novelty wears off. Winter is quickly approaching, and I need myself another tube amp project.

Here's My plan:
-Drop the op-amp/lead level control. Since I'll be going into a tube output, there's really no convenient way to include it without a bunch of extra circuitry. Will use a PPIMV in place of the standard master control.
-Drop all the switching circuitry, as it only switches two things, the clipping diodes, and the Lead Drive control which will be gone anyways. Will probably just control the clipping diodes via a switch on a push-pull pot.
-Get rid of the low sensitivity input. Don't see a need for it and probably won't have room.
-May or may not keep the local NFB loop around the PI, just depends on how it sounds. I may end up moving its input to the secondary side of the OT.
-Will need a +/-12V supply for the clipping diodes. Thinking I will make up a small board to supply it using a DC-DC converter and a few caps and rectifiers. Open to other suggestions though.

So I've attached the best quality schematic I could find as well as one of mine showing loosely what I want to do. The original is pretty damn hard to read, I've done the best I can to get the values right, but if someone wants to look them over and tell me what you think, I'd appreciate it. In particular, the control labeled pre-amp volume appears to be 25k, however that seems extremely low. Maybe its 250k? Its so hard to tell. However the input impedance even on the high input is pretty low as well so maybe that's correct. Also you'll want to open the schematic in Firefox and not the windows preview. I guess Firefox's interpolation/decompression algorithm is better, so its a bit easier to read.

Only major part I need is an OT. Got a choice of two PT's one that'll give about 330V on the B+ the other a Deluxe Reverb type which will be about 420 without a tube rectifier, both at 120mA. Thinking of going with the latter as I'm guessing most of the sounds this amp was used for weren't pushing the SS output into clipping so it might be nice to have the extra headroom, given that the sounds I'm going for are probably all coming from the pre-amp.

[10thTx]

Don't know if you've seen Sluckey's dual Marshall schematic and layout? Has some similarities to what you're doing.

With respect, 10thtx

[pompeiisneaks]

Very interesting, yeah I saw that Mr Carlson's lab last night. This one seems a bit better with the PI included. Are you going to have to get an additional PT to provide the current for the 6V6's? Or just swapping out the PT? Yeah I'm building that Sluckey Dual Marshall right now. Having a ton of fun doing it.

~Phil

[strelok]

Nope this a build from scratch. I have some parts laying around that I've been contemplating what to do with, PT, Chassis, and Head Shell. I already have a couple 2203's and that 6V6 Express I built a while back. I'd like to do a Rocket at some point but this chassis is already punched for Octal's. I didn't really want to do another Marshall type circuit since I'm pretty well set on that front, however this circuit seems to have enough changes to it that it should make for something different/interesting enough to warrant another build.

I haven't seen Sluckey's Dual Marshall before, but I did something similar on the last 2203 I built. Push/Pull pot that bypasses the cold clipper stage, so you get either a 2203 or 1959 bright channel. You don't have the option for the normal channel but I generally don't have much use for it anyways.

[Reeltarded]

Although that amp was never actually used on Eliminator, it was endorsed by (and sort of built with) Willie G (in mind). They are out of the box scrawnky as all hell. We had a 2x12 model around that was an avalanche of midrange gnarl that was a decent substitute for a tweed but loud enough to drive a room. It's a weird amp! They have the 50s Fender crying highend thing going on.

Big bottle Rocket is a good idea. Finally a chance to get the AC50 right. AC50 is pretty terrible. An EL34 Rocket could go to the Moon. (and maybe not burn on the launch pad) lol

You could pay homage to the Legend by putting a slope control in a Rocket.

[M Fowler]

The big bottle Rocket is a great amp and sounds great with EL34's, 6L6GC's, KT66, KT88's and KT120's. I've built lots of them and gigged for years with the reverb Rocket version.

But not much head room if you only use the smaller HT voltage 300-0-300. Better to use 325-0-325 or 350-0-350 PT's.

Mark

[Reeltarded]

2 votes for the space program..

[strelok]

Oh man, I'd love to build a big bottle rocket, especially with reverb. I'm not that big on reverb but something about the rocket with reverb just seems so right. However, I can't really justify it at this point. If I were to do another Trainwreck, I'd want to do it right. Proper transformers, a nice headshell etc. I'm kinda on a budget at the moment. Additionally I have 2 PT's that have been sitting around for years begging me to put them in something. Neither of which are really big enough for a Rocket, certainly not a big bottle one. That and I can't really justify the volume. I'm not in a band at the moment, loud guitars and apartments don't mix, so I'm pretty much relegated to playing cranked up amps in the small shop at work after everyone leaves. Which is great but even my little 15w express or 2203 will take your head off in the small space even with the 112 cab I play through. Even as I type this sitting right behind me is a Metroamp 100w 12 Series clone I built over a decade ago and a '66 Fender Bassman, neither of which ever gets played much these days because they're just too loud for the spaces I'm able to play in. So I'm saving the big(ger) guns for when I have more money and a place to play them in at the proper volume. VVR's, Attenuators, Master Volumes all work to some extent or another, but it just isn't the same as having something wide open, which is why I like these smaller amps so much right now.

So all that rationalization aside, I think I will go ahead with the cheeseball lol. Again its going to be built using terminal strips, so if I end up hating it I can have a different pre-amp in there in an afternoon. If it ultimately winds up being a 6V6 rocket or something like that, I'm not gonna complain haha. But for right now I'm on a weird retro 80s kick that can't be helped, "Good" is not the modus operandi here. Weird, stupid and cheesy is what I'm after. Who knows it might actually turn out to be something pretty cool. An experiment, what would a legend have been like, had they made them all tube?

Also with regards to Billy Gibbons and Legend where did you hear that amp wasn't actually used on eliminator? I found this series of articles where the engineer supposedly claims that's what he used, but idk:
http://www.woodytone.com/2010/09/28/gib ... e-rockman/
http://www.woodytone.com/2010/09/30/eng ... ator-gear/
http://www.woodytone.com/2010/10/05/bfg ... d-tidbits/