How to build a Marshall valve amp…

overview

Although this project was very complex, took me a few months to complete, and countless hours of frustration, this will be a very basic tutorial on how I did it, including small images and no great detail. Why? Because this project, unlike the others, contains lethal voltages that, if mistreated or misunderstood can and will kill you.

I had two close calls with this, one time having a component lodge itself in my scalp, and another, losing a fingerprint from my finger. luckily, I was not hurt more seriously, but for those reasons, I will not divulge too much on this project.

If you would like to build one of these yourself, please go to ::metroamp:: and order the kit, with instructions. Read them, learn them, THEN build it… 🙂

step 1

Ok first things first, order the kit! Seriously, trying to find all of these parts to specification is just too hard. I tried for about a year, and then gave up and bought the kit.

When ordering, you have the options to upgrade various parts. I have the basic kit, however later on, I upgraded the valves and capacitors and it sounds much better, so it’s up to you.

Once the kit arrives, ensure all the parts are there. take a close inventory, as getting half way through and realising you are missing a vital part would suck! It is always best to have all the parts ready to go, in case you feel like doing an all-nighter and wiring well into the night!

amp1

step 2

This may seem like a HUGE first step, but it is not complicated, only time-consuming. Basically you need to mount all relevant parts to the chassis and solder in all the main wires, as once the board is in, it is too difficult to do. The kit comes with a great diagram to do this, and all colours are specific (for example, later when they say measure on the RED wire, you know exactly where to check!)

This step took me about a week, however I was sitting in front of the TV while I did it, so for someone who wasn’t easily distracted, you could probably get this done in an afternoon or two.

It isn’t visible, however I have mounted the transformers, the choke, capacitors, valve sockets, input sockets, output sockets, pots, switches, fuse holders, ohm switch, power cable and of course the plexiglass front and back panels.

amp2

step 3

Next the empty board is mounted into the chassis. All relevant wires are then attached to the board, threading through their support holes and soldered to their mounting lugs.

Make sure when attaching to the lugs, that you wrap the wires around the lug, and do not insert it into the lugs hole. I used the holes to sit the components in, so when I was soldering, I could use two hands. It also makes removal of components easier, should you wish to upgrade the capacitors, or the circuit requires something be swapped over.

It is already resembling an amp, huh? Looks almost finished? Well, there is a LOT to go yet before you can safely plug it in…

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step 4

Next, install all components onto the board. Make sure that any polarised components are mounted the correct way (capacitors, diodes etc) as this could cause nasty damage later when it is powered up.

The end of the chassis has an empty area, which is a great spot to put the multimeter into, and attach the -ve pin to the chassis, so I only need to measure with one hand (and avoid electrical shock!)

It doesn’t look to complicated on the board, does it? that’s the whole amp right there, no other circuit boards in there!

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step 5

Here is a picture of the amp after it was modified with new Mustard Capacitors (yellow ones) and also the Electro Capacitors (blue ones) Although they are the same ratings and values as the ones that were in there before, they are a vintage part (or at least vintage replica) and obviously work differently internally (no idea, to be honest) but the sound is 500% better, in my opinion!

Hard to see, but in the top of the photo you might notice some masking tape and something white? I have made a copy of the schematics and put them in an envelope inside the amp, should I ever need to do repairs, they will be right there waiting for me!

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step 6

Once all internal wiring is done, and it has been checked, double checked and triple checked, make sure there are no loose fragments of wires or components floating around in there, flip it over upright, and install the valves!

Inserting the valves can sometimes require a little force (but not too much, they are made of glass!!) I used a circular motion, to ease them into their sockets, however one would not go in. It turned out there was a spot of solder on the underside of the pinhole, so double-check that! You can also use a switch lubricant (NOT WD-40!) to lube the socket a bit to help with inserting them.

These valves are the standard ones that were in the basic kit, however they worked well for me for about 3 years, so not too bad!

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step 7

Once all testing, measurements, adjustments, and biasing have been completed, assemble the chassis into the case and admire! These amps are a dying breed, and I now possess one that cost me about 20% of the retail cost to by a replica one!

Go easy on the volume for the first few hours, to allow all the components to get used to their new home, and then progressively get louder! As this is a valve amp, remember to allow the amp sufficient time to heat up, using the standby switch for at least 2 minutes before switching it on and playing. This will help the amp last a long time (especially the valves!)

Rollover the image for a view of the back panel, with all of its cooling vents to assist in keeping the valves as cool as possible.

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step 8

Of course, once it is completed, you can brand it in any method you like, either going with a Marshall logo (The one shown here is a replica of the first ever Marshall logo used from early 1960’s) or perhaps your own name or logo? or leave it plain to keep people guessing! completely up to you.

Overall, this build was a challenge for me, as I have electronics knowledge, however not in such a detailed and complex project. As I said earlier, it is dangerous, so if you are in any doubt, get someone else to do it, or simply buy one (with a warranty).

I am looking forward to many years of use from this amp, as they made them to last back then, and I believe that my work should stand the test of time!

amp8

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