BahHumbug's 5E3 project

BahHumbug

This week I took delivery of a 5E3 kit from Modulus amps.  Like many here I've been using valve amps for some years, but I'm also very curious about how things work and I've had a niggle about these for some time.  So I bought the kit, partly for the fun and fulfilment of building it and getting it to work, but also as a driver for a bit of learning.

I spec'd the kit as just chassis, transformers and components, no valves, speaker or cabinet.  I have most of the valves already in the spares box, and a Celestion V30, which I can use for testing while I ponder what speaker to look for.  Plus I'm intending to make the cab myself.  I've previously used all the practical skills on other projects, so I'm fairly confident of a non-disastrous outcome.  The only thing I haven't dealt with before is valves and the attendant high voltages and stored energy.  But, I'm aware of the dangers, and I have a careful approach (usually).  What could possibly go wrong?

The other part of the project is to write up a document, which not only describes how the thing works, but goes some way towards an in-depth analysis of the circuit.  I did quite a bit of electronics, circuit theory and the attendant maths in my degree (30 years ago), so there'll be a bit of reviving previously learnt knowledge, as well as (hopefully) some new learning and insight.  This bit has already started, as I got started on it as soon as I had ordered the kit.  It might be quite a big job though;  11 pages in and I'm still on the input stage!  I've already succeeded in reviving some stuff that learnt at uni and learnt some new stuff too, so its all good.

Ossyrocks

Have fun!

I built a Mission Amps 5E3 kit a few years ago. It took me three Sunday afternoons in total.

The best bit is coming to switch it on for the first time, it took me an hour to pluck up courage, but it worked perfectly first time.

I actually dealt the amp on for a profit in the end. I should build another!

Rob

stickyfiddle

Nice! I did my own 5e3 in December/January and really enjoyed it. I look forward to reading this thread as it goes on

BahHumbug

Thanks chaps.
@stickyfiddle I enjoyed reading through your build thread the other day.

I’ve got a few days of enforced downtime coming up late this week, so I’m hoping to make a start.

stickyfiddle

Cheers - it's a good ufn build. The main thing I found hard was the off-board wiring once the board was installed in the chassis, just as it's a bit tight. But it's doable, you just have to be careful

On speakers, I have a Celestion Blue in mine which sounds really really good, but is very loud. I have a Jensen on the way - will let you know how that compares.

BahHumbug

Yes I noted that you’d mentioned the fiddliness of the off board wiring, so I made a mental note to plan around that.  Thanks for the reminder though.

BahHumbug

Here we go with the build then.  I had half an hour free on Wednesday evening, so I went through the kit with the Modulus picklist and checked that everything was there.  Here's a quick photo of the kit contents.  The chassis seems like a particularly substantial beastie.  And I don't know why, but I'd kind of expected to have to build the turret board myself.  Still that's several hours of my life that I can spend do something more interesting

https://www.dropbox.com/s/64eah5fhvszl7dl/P1060465.JPG?raw=1

BahHumbug

I didn't order valves with the kit.  I already had a pair of 6V6s and was fairly sure that I had some 12AX7s lying around.  I bought a 12AY7 from @sharpjimbo, and a 5Y3 came from Hotrox.

I had a dig around for 12AX7s and found......

https://www.dropbox.com/s/81xtmfb0vw7adui/P1060467.JPG?raw=1

......eleven of them.  This is a throwback to a time when I thought it was really necessary to swap your valves out annually.

But which one will I use?

BahHumbug

So, on Thursday afternoon I had minor surgery to remove a lump from my left foot, that had been causing some discomfort.  Nothing malignant, the doc says, but now I have a sore foot and I can't get around so easily.  A great excuse to make some progress on a project.  I took an hour on Thursday evening to get my work area and tools and stuff together and made a start on the circuit board.

https://www.dropbox.com/s/xx1nku2v8lu6bh2/P1060471.JPG?raw=1

BahHumbug

I really got going on Friday morning, getting something like 2 to 3 hours in, although the progress doesn't look much for the time spent.

https://www.dropbox.com/s/9nrol3fd21st9pr/P1060473.JPG?raw=1

I think its easy to look at the task from the point of view of the components and think that there's not much to it, but when you add in all the wires, its a much bigger job.

On the subject of wires, the kit comes with 3m of yellow wire, for the signal path wiring.  It makes sense to make all the wires that are going off-board a bit on the long side.  On the other hand there are a lot of them so I was careful to be not too generous and risk running out of wire.  Now I'm a little concerned that I might not have been generous enough.  I'll find out when it comes to the fiddly bit getting it all in the chassis.

BahHumbug

Just over an hour spent on Friday afternoon and the board was done.  I'd done continuity checks on all the joints as I went along and these were ticked off on a copy of the layout drawing.

https://www.dropbox.com/s/wnaiv3sgwbxhvw3/P1060476.JPG?raw=1

https://www.dropbox.com/s/xjgiz562r07y4ll/P1060477.JPG?raw=1

Adam_MD

Looking good I've been wanting to build an amp for a long time but haven't had the time. 

stickyfiddle

That looks like enough wire on those leads. The only issue I had with those in my build was actually leaving them too long, then wanting to trim and strip them after I put the board in the chassis - getting my chunky wire strippers in was not a fun job, so I had to resort to my crappy small ones for a few. 

Looking good so far! 

BahHumbug

Wire stripping in the chassis is a bit of a concern for me.  I only have chunky wire strippers.....

sharpjimbo

BahHumbug said:

I didn't order valves with the kit.  I already had a pair of 6V6s and was fairly sure that I had some 12AX7s lying around.  I bought a 12AY7 from @sharpjimbo, and a 5Y3 came from Hotrox.

I had a dig around for 12AX7s and found......

https://www.dropbox.com/s/81xtmfb0vw7adui/P1060467.JPG?raw=1

......eleven of them.  This is a throwback to a time when I thought it was really necessary to swap your valves out annually.

But which one will I use?

Good stuff, I'm glad it'll see some use. I hadn't realised that you were building your own 5E3, that's awesome! I've been thinking about doing this for a while now. I'm guessing you've seen the recent 5E3 self-bulid That Pedal Show episode with Chris from Rift Amps? I've been giving some serious thought to buying a princeton kit, but like you I'm a little put off by the high voltages etc. I mean, I could just drop £700 on a reissue and not have to risk killing myself.

P.s., If you can get the wiring as neat as it is in this tread, I'll be impressed...

http://www.thefretboard.co.uk/discussion/151739/showing-some-love-for-the-princeton-reverb#latest

BahHumbug

I don't usually follow TPS, so I hadn't seen that episode, although I have just watched it this morning.  Very enjoyable.  That Chris chap knows his stuff.

I don't know that I'll be getting my wiring anywhere near that Princeton.  Speaking of which.......

stickyfiddle

BahHumbug said:

Wire stripping in the chassis is a bit of a concern for me.  I only have chunky wire strippers.....

TBH you can do most before you bolt it in the chassis - that's the thing I completely missed doing. If you really wanted you could get the leads the right length with it in the chassis, then remove it to strip the ends quickly, then reinstall for the actual wiring. 

I assume people who do this regularly just get good at knowing how much wire is needed for each connection.

BahHumbug

I think I spent 3 or 4 hours on it on Saturday.  Bolted in the valve sockets (fiddly M3 nuts and bolts) and wired up the heater wiring to the pre-amp and power amp sockets (the rectifier has a separate heater supply).

I've been using https://robrobinette.com/ as a main source for hints and tips, as well the information provided by Modulus.  The advice is to twist the pairs of power supply wires, and run them close to the chassis, in order to reduce mains frequency interference with the signal path wiring.  This is a bit of a fiddly pain.  The wires have fairly thick insulation, which doesn't really want to bend, never mind twist, so having twisted a pair together you are then fiddling to get them onto the valve socket terminals for soldering, while they are trying to pull in some other direction.  Fun! (Honestly, I am really enjoying myself).

Anyway, my wiring is what it is.  There do seem to be a number of different approaches taken for wiring runs and dress, some of which seem to contradict the instructions regarding keeping them close to the chassis etc, so I wonder how important that really is.

Here's the chassis, with the heater wiring in place and some of the other bolt-ons, er, bolted on.

https://www.dropbox.com/s/jq8z6ozvsshq7re/P1060483.JPG?raw=1

BahHumbug

Just like @stickyfiddle , this project has cats in it.  Daisy showed up just as I was bolting in the power transformer.

https://www.dropbox.com/s/jvdtzmiic2qt279/P1060486.JPG?raw=1

BahHumbug

The power transformer has given me pause for thought.  There are a load of wires coming out of it, which do various jobs.  Trouble is it doesn't match the Modulus drawing.  The wires are different colours (I can deal with that), but there are also a different number of wires.  I've found a drawing by the transformer manufacturer, so I can tell what each wire is for.  The tricky bit is the way the standby switch is wired up.  The Modulus drawing has more wires from the tranny for this and I assume is based around a tranny from a different manufacturer.  I've emailed Modulus, but its the weekend so it wouldn't be fair to expect a quick response.  I'm going to have to:

(a) Think hard about how to go about wiring up the standby switch, or

(b) Ditch the standby switch altogether.

Hmmmm

https://www.dropbox.com/s/l2iei6d2zy83d78/P1060489.JPG?raw=1

springhead

Trick for another time: get your two wires to be twisted.  Put one end of each in a clamp, vice or whatever.  Put the other ends in the chuck of a handrill - or I guess power drill that you can run very slowly.  Turn the drill to twist them together - you get a proper symmetrical twist doing this - not just one wrapped around the other.  Then what I normally do is leave the drill hanging, like a weight, for an hour or two.  This sort of sets the wires in place, stops them wanting to untwist.

Here's the mains transformer for my 5E3 build with some wires already twisted by this method:

Tight symmetrical twist gives better hum and noise cancellation.