No amp is for everyone....

[sliberty]

...but you also never know what might make all of the difference in the world.

Some of us find the Express to be tonal heaven. Others among us feel that the Rocket is pure perfection. Still others prefer the Tweed Deluxe, ODS, JTM45, Deluxe Reverb, etc.

I built an amp several years ago that I call the Uniwreck. It is a Univox U-1086 converted to an Express. The layout is not totally standard, but pretty close, and I did a few mods to it. I found it very aggressive for my tastes. Duh Well, it had some great tones, but I played a HiWatt through much of my youth, and the Express is not similar at all (except for the punch). The mods I applied included a split plate load resistor on V2a, a 12AT7 in V3, as well as a VVR. This amp stays at my drummer's house, and serves me very well. I really love it. But because it is at my drummer's house, I always forget how great it is, and how I changed some things.

Later, I built a more traditional Express. No mods, wood head shell, etc. I never warmed up to it. I tried 12AT7's in V1 and V3, but it still wasn't really my thing.

Still later, I built a Rocket, and really love that amp. So much so, that I built a Rocket combo conversion (was a Peavey Classic 50 - used at the Tursday night blues jam every week), and a Rocket with KT66's (still having some issues with that one).

I reached the conclusion that maybe an Express just isn't for me, and that I am a Rocket junkie.

Today, I went back to my traditional Express, and installed the split plate load resistor, like on my Uniwreck. This amp already had the two 12AT7's (V1 and V3) instead of the traditional 12AX7's.

Well, the results blew my mind. Now the amp has so much more headroom, and you can actually turn it up past 6 without it mushing out. And it still gets aggressive when cranked, but in a more contorlled way, whcih I consider a plus. I love the results.

I know that for those who love an Express in it's traditional form, this wouldn't please you. But for those who have always felt that the Express was a bit over the top, give this a try. It kills.

V1 = 12AT7
V2 = 12AX7
V3 = 12AT7

At V2a, replace 100K plate load resistor with a 22K resistor. Remove the wire that connected the 100K resistor to pin 1 of V2, and replace with an 82K resistor instead of the wire (direct to the socket if possible).

The mod couldn't be easier or more reversable, and the results are nothing short of astounding.

I hope some of you find this useful.

Steve

[don280z]

What are you using for a guitar? -- single-coils?..Humbuckers?....
any boost pedals?

[LeftyStrat]

Yeah, if one size fit all there wouldn't be so many different amp designs. But what you've done is IMHO the reason for building amps. First, most of us will never get our hands on a real Wreck or Dumble. And if we had one we would have so much money invested we wouldn't dare change anything.

I look at clones as starting points. I'm just interested in finding out what makes them special. But ultimately it's just learning techniques I can apply in my own designs towards building the ultimate amp for me.

Thanks for sharing. I'll have to try this on my Express.

[sliberty]

Mostly Les Paul Juniors and Teles.
Almost no pedals. Occassionally an AMZ MOSFET Booster.

[LarryLarry]

I tried the split resistor mod last night and it -definitely- gave my Express more headroom. It made the volume control much more effective in it's sweep instead of sounding like it's all the way up when it was only 1/3 turned up.

I don't have any 12AT7s to experiment with so I can't try that just yet.

At one point I had experimented with different value resistors from the input to pin 7 of V1 to tame it a bit and ended up with a 1k5 there. I'm now going to have to take it off and see how it sounds with just the split plate resistors.

[Bob S]

Thanks for sharing Steve.
I haven't bonded with my express either.
To be honest I was thinking about converting it to a big bottle rocket.
I always thought this strange because I really like the liverpool.
I tried the parallel v1 in my express & don't care for the results.
Maybe some more mods are worth a try.
If it doesn't work I foresee another rocket in the line up.

[sliberty]

Glad to hear this was useful and of some interest. What I didn't mention in my original post is that the split plate load ratio is tunable to taste. As long as the two resistors add up to about 100K (82K + 22K or 47k + 56k as examples), the amp will work perfectly well. And then, you can have fun with the tube choices. I use 12AT7's in V1 and V3, or sometimes just in one of those positions, but you can also try 5751's, and other similar tubes to your liking.

[M Fowler]

I took my Express and removed the presence circuit, replaced presence pot with 250kL treble cut pot and grounded the tail resistor, love the amp now.

Mark

[Clyde]

grounded the tail resistor

No feedback anymore Mark?

[M Fowler]

No feed back I grounded the tail resistor and use the cut control to get a better tone.

The amp still cuts through the mix and based on the guys that tried the amp at the local guitar store they really like it. Still an aggressive amp but to my ears it sounds better or should I correct that to say the amp fits what I like in an amp better.

One Express I put in 6L6 or 5881 can't remember and the other has EL34's.

Mark

[bcmatt]

I took my Express and removed the presence circuit, replaced presence pot with 250kL treble cut pot and grounded the tail resistor, love the amp now.

Mark

Hey Mark,
What exactly do you mean be removing the presence circuit? Would that be like having the presence control cranked? or all the way off? Do you still have the 100K NFB resister from the speaker? Sorry, I'm confused...

Then you added a cut control? Would that be after the PI like a DC30?

I'm just curious because I always run my presence all the way down on my liverpool, and then I also use a 5751 in V1. That's how I like it, but even still some speakers create too much high end fizzle for my liking. I can get my tone, but I'm wondering if I should be trying more mods to get the amp more fully in my ideal range with the controls.

Anyways, I'm wondering if I should hard-wire mine to the least amount of presence or change some values...

[Richie]

The presence or feedback circuit would have a less gain effect to the amp.
Although with presence it also has added highs with that control.
Removing the presence circuit would be like a gain boost.

A few suggestions. you can keep the presence feedback circuit, and change the value of the feedback resistor. Going from the 100k to a 47k or 27k down to a 820ohm like in a fender, will also give you an added notch of the more clean volume control. Meaning it won't have such a quick breakup when turning the volume control. But still should have plenty of gain toward 2 oclock.

I also like adding the cut control over the presence control.
You can also look into using a resonance control. Its kind of the opposite of presence,in it add or thickens up the bass sound.
And i think someone put a presonance control. which i believe does both?

If you like trying different things, besides subbing tube types. Try using 47k or 56k plate resistors in the PI. and change the cathode of the PI to 560ohm 680 ohm . and still use either 12ax7. Might also look at some tube data besides the gain factor of the tubes used.

forgot to add, you could put the presence or resonance circuit on a pull switch, if you wanted to remove or flip out the circuit. I would set or select it first, as it would probably thump when switched.

[M Fowler]

I took my Express and removed the presence circuit, replaced presence pot with 250kL treble cut pot and grounded the tail resistor, love the amp now.

Mark

Hey Mark,
What exactly do you mean be removing the presence circuit? Would that be like having the presence control cranked? or all the way off? Do you still have the 100K NFB resister from the speaker? Sorry, I'm confused...

Then you added a cut control? Would that be after the PI like a DC30?

I'm just curious because I always run my presence all the way down on my liverpool, and then I also use a 5751 in V1. That's how I like it, but even still some speakers create too much high end fizzle for my liking. I can get my tone, but I'm wondering if I should be trying more mods to get the amp more fully in my ideal range with the controls.

Anyways, I'm wondering if I should hard-wire mine to the least amount of presence or change some values...

Removed the presence pot, removed the 100k resistor to speaker jack and then soldered ground wire to the tail resistor. I've tried reducing the NFB resistor in the past as well as moving the 100k NFB resistor to different OT taps. I just don't like a presence control. I think one could always just reduce the NFB resistor and leave it in the circuit as non-variable (no pot). But I like a cut control to add darker tone. The Rocket has the cut control I'm talking about.

The other options are leave the presence and add a resonance control or change the presence to a presonance control.

I get a lot of advice from Richie he knows what he is talking about

Mark

[hans-jörg]

Glad to hear this was useful and of some interest. What I didn't mention in my original post is that the split plate load ratio is tunable to taste. As long as the two resistors add up to about 100K (82K + 22K or 47k + 56k as examples), the amp will work perfectly well. And then, you can have fun with the tube choices. I use 12AT7's in V1 and V3, or sometimes just in one of those positions, but you can also try 5751's, and other similar tubes to your liking.

Hi,

that means you wired it as a fix "graduate" like the Komet but without the possibility to come back to a "fast"-mode.

Isnt it a kind of strangulation?

I built once a test-K60 with this switch. The "graduate" is nice to have but only that - I miss the power.

Actually I build an Express too (it was a Liverpool before, and my hart still hurts) with the split load but with the switch.

Thinking about the presence too - would be the whole time down, so why not better the High Cut, especially when I want to implement a LarMar. The Presence would be useless. NFB stays with 56k.

Hans-Jörg