5E3 Scratch Build

Wrench66

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Hi everyone. I hope everybody is staying safe in quarantine.

I've been planning this build for a long time now. My goal was to scratch build an amp. I've built two clones from kits, both Tubedepot kits, and they were a lot of fun, but I wanted to get a little more creative. Originally, I was planning a PTP build, but I kinda lost my nerve at the last minute and went with a turret board instead.

I found this aluminum tray a few years ago and immediately knew I wanted to turn it in to an amp chassis. It's quite a bit larger than your typical 5E3 chassis, 15"X12"X2", but I figure that might make it easier to work. The material is pretty thin at 0.06" thick, probably a little to thin to make a chassis out of, but I think it might work. Below you can see it after I machined the holes for the controls, tube sockets, transformers, etc.



It looks like the tray, box, or whatever it was originally may have been a school project or something. It kinda looks amateurish, so it should fit right in with this build. :cheers2:

One thing I will admit right from the start is that I cannot for the life of me drill a straight hole. :mad: I spent hours laying out the chassis and accurately center punching each hole only to have the drill wander anyway. They aren't off by much, but it really got under my skin. The only thing I can think of are the cheap POS Dewalt drill bits I am using. Well that and a lack of skill I'm sure. :rofl: It's ok though as long as I am learning something new.



Here is a picture of the turret board. I basically modeled it after the 5E3 eyelet board, although it is slightly longer and wider than the stock board. My first turret board experience was my 1974x clone. It was a blast to make and they are so easy to work on compared to printed circuit boards. It's these two reasons why I went with a turret board for this build. I have no experience with eyelet boards yet.

I'm using the small parts kit from Mojotone. I ordered the transformers from another vendor and have those on hand as well. There will be more posts in the coming days as the build progresses.
 

Cjsinla

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Good luck with your project. My first real build was the 5f1 on an eyelet board. They are very easy to work on, may be easier than turrets but turret builds are a little easier to modify later. If you ever decide to tackle a PTP project I recommend the Mojotone GA5. Makes a great practice amp.

F6B4F25A-33AA-42D3-A39C-E3821D8A6DF8.jpeg


In this pic I see that the electrolytic cap on V1 is backwards. This was a work in progress pic. I can’t remember if I switched it around prior to firing it up. I’ll double check tomorrow.
 
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Soul Tramp

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This would be a great project to learn how to locate the OT in a way that minimizes hum and lowers the noise floor. MANY of the old amps paid little to no attention to noise floor and grounding schema.

The PT produces a magnetic shadow that induces hum into the OT. Depending on the design of the PT and location of the OT, this can be increased or decreased.

The way you experiment with this is as follows:

1) Mount the PT, but don't connect any of the secondaries. Have the primaries connected to the power switch.
2) Place the OT where you intend to mount it but don't bolt it down and don't connect any of the OT wires.
3) Temporarily connect a speaker or headphones (I use my noise cancelling headphones) to the OT secondaries.
4) Power up the PT and listen to the OT via speaker or headphones.
5) Slowly rotate the OT and move it away from the OT, you will hear the hum get louder and quieter as you do.
6) Pick a spot that reduces hum and allows for efficient connection of the OT primaries & secondaries.

A flat mount PT produces the most optimal magnetic shadow most of it goes up and down. An upright PT creates a shadow the radiates out across the top of the chassis and creates the greatest interference with the OT.

Rotating the OT relative to the PT will greatly reduce hum.
 
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Wrench66

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Good luck with your project. My first real build was the 5f1 on an eyelet board. They are very easy to work on, may be easier than turrets but turret builds are a little easier to modify later. If you ever decide to tackle a PTP project I recommend the Mojotone GA5. Makes a great practice amp.

View attachment 452098

In this pic I see that the electrolytic cap on V1 is backwards. This was a work in progress pic. I can’t remember if I switched it around prior to firing it up. I’ll double check tomorrow.
Thanks! A GA5 is definitely on my list of amps to build. Single ended might be the way to go for my first PTP build.
 

Wrench66

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Here is today's update! It is basically done already. It all went pretty fast once I started.



You can see the fuse, power switch, lamp and controls on the far side. The turret board came out all right I think. I ran the vast majority of the connecting wires under the board to the bottom of the turrets. I probably won't do that next time. It turns out the wire routing hole I drilled on the right side wasn't needed.

The extra room made soldering much easier. I'm a little concerned about noise from the long signal wires, but I'll install shielded wiring as needed if noise is a problem.

I also used a ground bus which is a departure from the layout Mojo tone used. You can see it as the bare wire at the front of the board. All of the pots and jacks are grounded to the ground bus and then the ground bus is grounded to the front right PT lug in the picture. I got the idea of the ground bus from the 1974x clone I built a few years ago. I don't know if it makes any difference, but it makes more sense to me than having the duplicate grounds through each of the pots, jacks, and the lug. Again, if noise becomes a problem I'll modify the layout here to correct it.

The PT is a Classic Tone 40-18078. The primary side has connections for 100, 120, 220, 230, and 240VAC. Of course I used the 120VAC connections here in the US. You can see the unused connections are insulated and tucked out of the way to the left of the PT. The secondary has connections for 330VAC and 355 VAC. I'm using the 330VAC taps in hopes it breaks up a little sooner. It also has a center tap for the 6.3VAC filaments, which is why I'm not using the virtual center tap.

The OT is a Classic Tone 40-18090. It has 8Kohm primary and 4, 8, and 16 ohm secondary. The speaker I plan to use is 8 ohm, so the others are insulated and capped (orange and yellow wires in the center).



Just another angle of the interior showing the back of the amp.

You can see red fingernail polish on the rectifier socket mounting screws. The screws that came with the Mojo Tone small parts kit are garbage and one of them stripped the threads off before it was anywhere near snug. I drilled it out and found some stainless screws and nuts in my stash. The only down side was that the nuts were not self-locking, hence the fingernail polish.

I powered it up without tubes using my dim-bulb tester just to check the filaments and the 330VAC taps. The filaments checked perfect. The 330 VAC taps were pumping out over 400 VAC, but I figure it will be high until I stick some tubes in there. Good news is that it didn't catch fire or electrocute me, so I figure thats enough for one day.
 

Wrench66

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Well I think the chassis is complete! I put some older tubes in and powered it up. All of the voltages are very close to the voltages shown on the Mojo Tone layout.



I've spent the day playing it and it really sounds amazing! It's really quiet until I plug in a cable. There is a very slight hum when the amp is on and warmed up, but I have to really listen for it to hear it. There is a bit of hiss especially on the bright channel when it's turned up past noon. Again, it's not over the top intrusive, but it is there. I've read somewhere that carbon composition resistors make a hiss sound and that modern metal film resistors are much quieter. I'm pretty sure Mojo Tone sent carbon composition resistors in the kit. I mean they look old school, so... :dunno:

So, I've spent the day playing it. First of all, it is loud as hell. It's every bit as loud as my 18 watt Marshall clone. That's to be expected since it does have two 6V6s. Depending on the settings, the bass is out of control! I mean shit was being shaken off the walls, but I kinda got the hang of the controls after a while.

The normal channel seems excessively dark to me. And that's saying something since I normally prefer a darker sound. I noticed that the louder I run it the darker it sounds. The bright channel is bright as the sun on a clear winter's day with the volume low, but it also darkens as the volume increases, although not to the extent as the normal channel. The tone control seems useless when either channel is turned up.

So, there is the whole interactive volume control thing going on with this circuit. It's not intuitive at first, but after a bit of fiddling with the knobs I started to get the hang of it. LOADS of gain on the bright channel when the normal channel is low or off all together. I mean it's loud and crunchy at 9 o'clock on the volume (I only have humbucker loaded guitars). At noon it is noticeably darker, but a really nice sizzle over the top of everything. By 3 o'clock, there is no cleaning this thing up, but it still sounds really amazing although maybe a little to dark. Near the end of the bright channel volume sweep, there is a noticeable drop in output and kind of a sputtering (?) feel to the notes that really reminds me of my 5F1 when I push it's volume past the 11 or so.

So I'm really digging this thing so far. I'll keep playing over the next several days to get a good feel for how it plays. I'm inexperienced with how these things are supposed to sound. I would appreciate it if any of you more knowledgeable folks would chime in if you see problems with my description above.

If I could nit-pick at all, I'd say it's a tad dark when turned up. I'm playing it through a MIC greenback which was much to bright for my 18 watt clone, so it's surprising to me that it is that dark. But it isn't unpleasant at all. It's difficult to describe, but it's got a nice character to it even if it is dark.

So that I don't electrocute myself moving it around, I made a temporary base out of 1/2 inch shitbox plywood. My plan is to either make a head shell for it or make a combo cab for it. Not real sure what direction I want to go in that regard right now.

I had a short cellphone video my wife had taken of me playing it, but it's to big to load here. I'll try to post some sound clips in the coming days.
 

Soul Tramp

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Well done! So, what are we building next!
 

Wrench66

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Well done! So, what are we building next!
Thanks! My next build will probably be the PTP GA5 mentioned earlier. Or maybe a tweed vibrolux circuit... But first I have to build a cabinet of some sort for this one.
 

Cjsinla

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Thanks! My next build will probably be the PTP GA5 mentioned earlier. Or maybe a tweed vibrolux circuit... But first I have to build a cabinet of some sort for this one.
I recommend both these amps. With the 5e3, you might try playing with the caps. I’m told that Fender used .022 coupling caps on V2 in the handwired Edge U2 version. I went the other way, I put my .022’s on V1 instead. These mods pass more high end through. The bass on a 5e3 seems over the top otherwise and the amp still grinds when you turn it up.
 

Case24

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The interaction of controls is very familiar to me. I built my 5E3 10 years ago. When the Bright channel is maxed it is identical to the Normal channel; the bright cap is doing nothing at this point. For a cleaner setting, set the unused channel on 8 or 9 and the channel you are plugged into on 3 or 4. The opposite to dirty it up. I run my tone control around 8 or 9. Have fun! Great build.
 

Wrench66

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I recommend both these amps. With the 5e3, you might try playing with the caps. I’m told that Fender used .022 coupling caps on V2 in the handwired Edge U2 version. I went the other way, I put my .022’s on V1 instead. These mods pass more high end through. The bass on a 5e3 seems over the top otherwise and the amp still grinds when you turn it up.
I will say this is the darkest amp I’ve ever played and the bass can get out of control depending on settings. The thought of modding it came within minutes of playing it for the first time. I’ll put some more play time into and try to get a good understanding of it first though.
 

Wrench66

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The interaction of controls is very familiar to me. I built my 5E3 10 years ago. When the Bright channel is maxed it is identical to the Normal channel; the bright cap is doing nothing at this point. For a cleaner setting, set the unused channel on 8 or 9 and the channel you are plugged into on 3 or 4. The opposite to dirty it up. I run my tone control around 8 or 9. Have fun! Great build.
Thanks! So far I favor the bright channel at about noon with the tone at 3 or 4 o’clock. I’ll try a 12ax7 in v1 and jumping the channels in coming days.
 

el84ster

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Nice work! And show that if you do
Certain things right, some rules can be violated (long grid wire runs) and still work ok.
I’d double check your volume and tone control wiring. The tone should get brighter as you turn the volumes up. Somethings not right there.
As far as all the bass, they can be bassy but the originals were paired with vintage jensens which has relatively little bass response. So speaker choice is crucial. Something like a Celestion vintage 30 would have way too much bass for this circuit. Not sure what speaker you’re using.
 
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el84ster

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Another tip if you want to get the noise down:
The quietest amp will have only 2 ground points. One in the preamp area (input jack works great) and one in the power section.
everything in each area grounds to its repspective spot. Included in the preamp ground is also the filter caps that filter the preamp. From the Phase inverter on all things get grounded at one spot in the power section (usually a bolt of the power tranny).
This is a quieter layout than a ground bus and certainly quieter than random ground.

just remember that having a resistance (the chassis or other metal) between ground points will develop a small voltage that we can hear. So one point eliminates that.
 


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