The British Bomber - EL84 amp

[XgamerGt03]

Hey everyone,

I've been working on this amp for a little while now. It was designed to get tone that can go from Vox cleans and Vox grit all the way to some Marshall scream.

So the amp is one channel, the controls are Treble, Middle, Bass, Volume, and Boost. The Boost control allows manipulation of the amount of gain in the circuit without really changing the tone of the amp much.

The tube set up is as follows
V1: 12ax7 V2: EF86 V3: 12ax7 V4-7: EL84 and V8: 5U4G

For now the speaker is an Emience Texas Heat, but I want to get a Celestion AlNiCo Blue or Weber Blue Dog to test it out with that. The amp is LOUD too. It has no master volume so I'm going to either get a Weber Mass or build an Airbrake so I can lower the overall volume while turning the amp up more.

Here are some pictures of the amp as the build was in progress.

[IMG:640:383]http://img35.imageshack.us/img35/9602/imag0025hc.jpg[/img]

[IMG:640:383]http://img694.imageshack.us/img694/661/imag0052c.jpg[/img]

[IMG:640:383]http://img189.imageshack.us/img189/4822/imag0054k.jpg[/img]

[IMG:800:478]http://img861.imageshack.us/img861/3290/imag0067w.jpg[/img]

[IMG:800:478]http://img836.imageshack.us/img836/8099/imag0068e.jpg[/img]

[IMG:800:478]http://img855.imageshack.us/img855/7301/imag0069x.jpg[/img]

[IMG:800:478]http://img146.imageshack.us/img146/1294/imag0070b.jpg[/img]

Mach 5 Amps is an interesting name that a guy I do amp repairs for came up with.

So far the amp is quite awesome. It is very loud and achieves most of my design goals. The boost control works very well for changing the character of the amp. At its lowest setting you can get some nice vox grit at lower volumes, and as you turn it up the amount of gain increases a lot.

I have a video with a bit of a sound check with the amp. I injured my hand earlier this week and haven't played guitar since a car crash five months ago made me sell all of my gear to pay bills and buy groceries.
http://www.youtube.com/watch?v=5zQsgVJyGB0

Let me know what you guys think or what you want to hear from it. I have a friend coming up this weekend to really put this amp through some trials.

[Noval_novice]

Congratulations on your new build! Looks good. Who did your faceplate? Would like to hear some clips with it turned up, though.

[Darkbluemurder]

Congratulations! Nice looking amp.

The tube set up seems to be Prescription inspired, correct?

Have fun,
Stephan

[XgamerGt03]

Congratulations! Nice looking amp.

The tube set up seems to be Prescription inspired, correct?

Have fun,
Stephan

A bit more than likely. I'm guessing that is the amp Dr. Z did for Paisley? If so then yes, I heard brad play one of them live a number of years back and thought the amp was pretty awesome.

I also liked the idea of using the EF86 as a gain stage later in the amp and have been toying around with it for awhile, so I came up with this. The EF86 circuit is essentially lifted from all of the old EF86 input stages you see, but the boost control is used to vary the gain of that stage. It really works well to increase the gain of the stage without adjusting the tone all that much.

Tone stack is a typical Fender TMB stack, it works well enough for me so why change it if it isn't broken? The input stage is in parallel.

Those Edcor Transformers are awesome, the output one is rated for 65W.

I need an attenuator or to install VVR in this amp though, the monster is loud... louder than any other 30W amp I have ever had or built.

[M Fowler]

How is your boost function wired?

In your video you showed it's function but I didn't notice that it actually bring on gain.

But you did keep the volume way down on purpose, I understand, so it was hard for me to hear any changes.

Hey I hope your injuries heal well.

Mark

[XgamerGt03]

Mark,

The boost control is a 50k potentiometer wired as a variable resistor in series with the cathode bypass cap. So at full the EF86 is completely bypassed, which leads to a huge increase in gain. I may in the future just change that out for a switchable cathode bypass capacitor.

It was a bit later in the day so I didn't want to tick the neighbors off, this weekend I'll crank it and get some clips.

[RJ Guitars]

... The amp is LOUD too. It has no master volume so I'm going to either get a Weber Mass or build an Airbrake so I can lower the overall volume while turning the amp up more...

Nice looking build - sorta like the Trainwreck Rocket with the other AC-30 channel - could be a popular idea.

Loud is relative observation but 30 watts is 30 watts ...that is loud when your in the room with it, especially if you have an efficient speaker cabinet. Have you looked at the Trainwreck pages and seen the Master Volume ideas he has there? One popular iteration of the #2 MV presented there that is going around lately is the PPIMV. This seems to work well on the EL-84 quad. It's a simple add on and you can even put the control in the back.

Do you have any clips of the amp cranked up?

would be cool to hear.

rj

[XgamerGt03]

... The amp is LOUD too. It has no master volume so I'm going to either get a Weber Mass or build an Airbrake so I can lower the overall volume while turning the amp up more...

Nice looking build - sorta like the Trainwreck Rocket with the other AC-30 channel - could be a popular idea.

Loud is relative observation but 30 watts is 30 watts ...that is loud when your in the room with it, especially if you have an efficient speaker cabinet. Have you looked at the Trainwreck pages and seen the Master Volume ideas he has there? One popular iteration of the #2 MV presented there that is going around lately is the PPIMV. This seems to work well on the EL-84 quad. It's a simple add on and you can even put the control in the back.

Do you have any clips of the amp cranked up?

would be cool to hear.

rj

I tried a crossline master volume ala Matchless and it killed all of the character of the amp, and the volume stayed low. I was disappointed with it, if that is what it does to a matchless amp then you have to wonder what its like without that master volume.

I need to look into the master volume you talked about and get the resistors I need while at work today. The back as you can see was originally intended to have a master volume, which is where it will be going.

There will be some clips this weekend with the amp cranked up and a friend who is a great guitar player doing the demo.

[rp]

I keep seeing more of that Edcor blue. I just got a 5K 10W champ one today - you can feel the quality holding it, they do really nice work. The little extras: spec label on bottom, 'made in usa' and 'edcor' decals, and blue bells, really shows pride. I hope it's not too good - super-husky and M6 and all that.

[RJ Guitars]

On top of the great look, Edcor also uses top grade wire for the hookup leads... everything seems first rate.

rj

[XgamerGt03]

I installed a PPIMV today, used a dual 1Meg pot with 1Meg resistors between ground and the wiper. The results are quite awesome. I can turn teh amp down to bedroom levels without losing too much of the sound from the preamp.

I do lose the power tube saturation, but the amp still sounds amazing. I might get another clip of it sometime today to hold everyone over until my friend gets back from spring break. So it should be sometime this or next weekend that he puts it through the ropes.

[XgamerGt03]

So I did finally get a clip with some higher gain and better guitar playing. Volume is still fairly low to avoid overloading the camera.

http://www.youtube.com/watch?v=QN1X-P4-izg

[xtian]

So I did finally get a clip with some higher gain and better guitar playing. Volume is still fairly low to avoid overloading the camera.

http://www.youtube.com/watch?v=QN1X-P4-izg

You're running thru that unmounted speaker on the floor? Well. That will be a different experience when you plug it in to a cabinet! The build sure looks nice, though.

[surfsup]

wow I see the preamp tubes are under the circuit board. Interesting...did you wire those leads up first?

[Darkbluemurder]

I installed a PPIMV today, used a dual 1Meg pot with 1Meg resistors between ground and the wiper. The results are quite awesome. I can turn teh amp down to bedroom levels without losing too much of the sound from the preamp.

I do lose the power tube saturation, but the amp still sounds amazing.

That one is surely better than that crappy cross line master. I have had very good experience with the LarMar PPIMV, which is a dual 250kA pot with 2M2 resistors between wiper and ground.

Cheers Stephan