there comes a time in a mans life when he needs to build an express

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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norburybrook
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there comes a time in a mans life when he needs to build an express

Post by norburybrook »

well, that time has come. I've started an Express/Komet type build. My transformers are too large to fit in the traditional way so I'm mounting them side by side, lets hope it's not a sonic issue. My OT is a Marshall plexi one so it's half the resistance of the express transformer, I can adjust with the impedance selector if I want I suppose or get a new transformer wound to spec if needed, however I don't think it will be an issue. I'm not a purist so let's see how it goes.

Spent today drilling out the chassis which was a Rocket chassis so needed a lot of modifications.


I've put a grommet in the rectifier valve cover for the OT cables as it's the nearest place to get the cables through leaving space for the filter cap stack.

so I've started....
DSC_1563.JPG
DSC_1564.JPG


Marcus
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joeboo88
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Re: there comes a time in a mans life when he needs to build an express

Post by joeboo88 »

Nice. Did you build the turret boards yourself?

It should be a cool amp. buy some earplugs
I think building something like a jcm800 2204 the sound is like a punch in the gut.
Building an Express the sound is like a punch in the face.
Keep us posted... :mrgreen:
Last edited by joeboo88 on Mon Sep 11, 2017 1:25 am, edited 1 time in total.
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

I will. I tend to document all my builds quite fully..warts and all. My view is there'll be someone less experienced who will benefit from a thorough build log, I know I did a lot of reading before jumping in with my first Dumble build. I'm still a novice but am enjoying the journey.

I got all the parts from Mike @ modulus amplification in Scotland. I think he's ampMike here on the forum. Great guy and a great resource for us guys in the UK.

Mains transformer from InMadOut in Italy, OT an old Dagnal I had lying around, lets see how that goes.


TBC


Marcus
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

Ok, got a few parts I need to order so have been doing a bit of reading.

couple of questions:

grounding......should I follow the original express layout with bus bar across the pots, or do it Dumble style with a bus bar elevated........or none of that and do the Larry grounding ?


2: I'm putting the Komet fast/slow switch in, which is a plate voltage divider(I think) . Now.....looking at some pictures of the Komet 60 it looks like the switch is before the cap to the next stage, wouldn't that mean you've got B+ voltages going to a metal switch? shouldn't there be an extra capacitor and wired so the switch is after both caps, and then on to the next stage? and what's the deal with the wire coil around those cables, is it some sort of inductance shield, and how is it made and where is it attached?

M
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

some progress while I wait for parts.

still unsure about grounding and the fast/slow switch.
IMG_20170912_171303.jpg

M
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pompeiisneaks
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Re: there comes a time in a mans life when he needs to build an express

Post by pompeiisneaks »

norburybrook wrote: Tue Sep 12, 2017 11:01 am Ok, got a few parts I need to order so have been doing a bit of reading.

couple of questions:

grounding......should I follow the original express layout with bus bar across the pots, or do it Dumble style with a bus bar elevated........or none of that and do the Larry grounding ?


2: I'm putting the Komet fast/slow switch in, which is a plate voltage divider(I think) . Now.....looking at some pictures of the Komet 60 it looks like the switch is before the cap to the next stage, wouldn't that mean you've got B+ voltages going to a metal switch? shouldn't there be an extra capacitor and wired so the switch is after both caps, and then on to the next stage? and what's the deal with the wire coil around those cables, is it some sort of inductance shield, and how is it made and where is it attached?

M
My opinion on grounding is that doing it against the pots isn't a smart idea, it can damage pots. I like a buss bar that connects to ground at one end and ties off at the last ground on the pots. Then I can bring in other grounds in the preamp to it, and separate the PI and Power grounds direct to chassis closer to the PT/OT area.

I don't know enough about the second question to intelligently answer ;) My opinion would be, though, to build the original express first, and if you really love it as is, you're done, if you think adding the Komet switch in may add something, then go for it.

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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

Phil, I agree about soldering the bus bar to pots which is why I first started thinking about it. I ;m going to go with the bus bar elevated like the Dumble builds I've done.

I'm sure someone will chime in about the fast /slow switch :D


M
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

Finished :D

Well after a few years of doing this, I've finally made and amp without any errors for the first time. even got the OT primaries the right way round.

Fired up first time no issues :D

Again not the prettiest compared to builds I see on here but it's quiet, no grounding issues, success.

So...thoughts?...........GAIN!!!!!!! to much gain for me, I need to calm it down for it to be usable for the kind of music I do, or maybe its a special occasion rock amp.


It's running about 380 on the plates so what should I bias at fro EL34's? It's sat here at 40ma at the moment just settling in.
IMG_20170918_182022.jpg

As it's all sounding good should I bother shortening the OT primaries and cable tying cables etc?

Marcus
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martin manning
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Re: there comes a time in a mans life when he needs to build an express

Post by martin manning »

That looks quite good Marcus, I've seen much worse! I'd go with about 45 mA... It's the same simple calc as always, assuming 65-70% Pa max: 25*0.65/380 = 43, at 70% it's 46. You can check the OT phasing and get the primaries the right way around first time every time, but it seems most people just take their chances. My Express has a trimmer in place of the 100k on the V2a grid, which is pretty effective at dialing down the raucousness. The Build thread is here: http://ampgarage.com/forum/viewtopic.ph ... 915&hilit=
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

Thanks Martin, I did a quick calculation at 60% of 25w so 40ma was spot on, I actually just put the trimmer to mid way and that's where it was.

I think this is the first build I've done without your help at some point.

I'm waiting for a DPDT switch for the fast/slow so I'll see how that goes.

I've also looked at the Komet pre amp and there's 'a couple of extra resistors which I think are a voltage divider to reduce gain, I might look at that too.

so you've got a 47k and a 100k trimmer in place of the 150k on the express? I think I have a 100k trimmer from an old build lying around, might try that.

Otherwise a PPIMV will be easy to try.

Need to make a cab now.

M
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didit
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Re: there comes a time in a mans life when he needs to build an express

Post by didit »

Little late but recalled past novel design based on Trainwreck, and using a Marshall OPT -- Junkbox Trainwreck. Lots to glean, with bit of attention.

Best .. Ian
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

thanks for the replies.


Ok today I tried a few things. I put an AY7 in and that does indeed cut the gain in a good way so I'd say that's the first thing to try if you want less gain.

I then put the AX7 back in and added Martins trimmer pot and 47k resistor. I'm not sure if this is working properly as nothing much seems to happen when I adjust the trim pot.....here's picture.

the wiper goes to the pin on V2.
IMG_20170919_184308.jpg



I then added a PPIMV , which was a 1M audio pot wired in to the 220k PI resistors. This does work however nothing much happens for the first half turn, everything seems to happen in the last 1/4 of the range.
IMG_20170919_184421.jpg


is this normal, or can it be tweaked so there's a more usable range?


Marcus
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romberg
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Re: there comes a time in a mans life when he needs to build an express

Post by romberg »

norburybrook wrote: Mon Sep 18, 2017 5:34 pm So...thoughts?...........GAIN!!!!!!! to much gain for me, I need to calm it down for it to be usable for the kind of music I do, or maybe its a special occasion rock amp.
Have you seen this video by Glen Kuykendall?

https://www.youtube.com/watch?v=Uc3Xi6aAG80

A whole lot of the express vibe is dialing down all that gain using the guitar's volume pot. You can get a pretty nice range of tones that way. Glen has posted on this forum details about guitar volume pots that work better than others with an express. Might be worth some experimentation before rewiring the amp.

Mike
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norburybrook
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Re: there comes a time in a mans life when he needs to build an express

Post by norburybrook »

thanks MIke, I have seen that in the past but it was good to watch again. I had a good play with the amp yesterday when tweaking and it behaves exactly like the one in the vid.

If you notice even with volume on 2 it's not 100% clean when you hit the strings a bit harder, which is fine for certain things but I'd prefer to be able to have clean with the volume a bit higher. Did you notice the amount of hiss coming through due to the gain? this is fine when you're cranked but when your guitar volume is on 2 for a clean sound there's a lot of background noise.

I'm going to continue to play with the amp and 'learn' how to use it. As I said in an earlier post maybe its an amp for just certain sounds/material and should be used in that way. Bit like having a 4x4 car for winter and not trying to make it a summer sports car.

It's an incredible amp though, by the end of the day I was really starting to understand how special it is.

I wonder if the Komet 60HD is significantly different, I don't have the fast slow switch on mine yet so that's another area where the gain can be reduced.

quite often I spend time trying out different tweaks, which is good because I learn what stuff does, but then go back to how the maker intended it to be in the end.

I really like the cut control on this amp, and the master volume works nicely to take the edge of things so they're a success and are staying.

M
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Re: there comes a time in a mans life when he needs to build an express

Post by martin manning »

Hi Marcus, the trim pot and 47k replacing the 150k is intended to produce a 10 dB cut. You should connect pin 3 to the coupling cap coming from V1b, pin 2 (the wiper) to the grid of V2, and pin 1 to the 47k, which is connected to ground. Turned all the way down you have a 47k/147k divider.
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