BahHumbug's 5E3 project

BahHumbug

Here's the donor cab in bits........

https://www.dropbox.com/s/y14k8401nwml757/P1060627.jpg?raw=1

I'd made the mistake of sticking the tolex on with spray adhesive, which meant that it was never stuck at all, and was really held on with staples.  So, once I'd pulled all the staples out it pretty much fell off.

https://www.dropbox.com/s/wkwkmp3vqhivk1x/P1060628.jpg?raw=1

The downside of the spray adhesive is that I was left with basically an unpleasantly sticky cabinet.  A root through the garage turned up a can of motorcycle degreaser which dealt with the stickiness quite nicely.

I've used Modulus amps' DIY 5E3 cab plans, which thankfully revealed that the finished cab would be quite a bit smaller than the donor cab.  So I cut down the cab into bits of roughly the right sizes.  I can't saw straight to save my life so everything was done a bit oversize and was then trued up with a mix of electric and hand planing.
I'd done the donor cab with butt joints reinforced with 6mm ply wafers set into routed channels.  This has turned out to be really solid, so I've done the same again.  Here's the bits ready for gluing.  Notice that lazy bones deliberately left one of the original corner joints uncut, to save on rejointing it.

https://www.dropbox.com/s/qvw7cl8zpvedau8/P1060629.jpg?raw=1

The obligatory 'all clamped up' shot:

https://www.dropbox.com/s/998eadbuisxktsg/P1060630.jpg?raw=1

Glued, front faces trued and rebated to accept the baffle strips:

https://www.dropbox.com/s/vwjfc5jqn3usmih/P1060632.jpg?raw=1

....and with the baffle strips glued in:

https://www.dropbox.com/s/40fm4dcv5tpuxd3/P1060635.jpg?raw=1

Still quite a bit of finishing-off work to do, but I couldn't help wanting to get the chassis mounting holes drilled and do a test fit of the chassis:

https://www.dropbox.com/s/8dgb2btpqhatzqi/P1060634.jpg?raw=1

poopot

While it’s all in bits... fit a VVR...

That’s a layout I did for the VVR I fit into the 5e3... works really well at getting cranked tone at very low volume...

R1 = 10ohm 5watt
R2 And R3 = 100kOhm 0.5watt
D1 = 12.1v 1watt zener
mosfet = either 2SK2968 or NTE2973
pot = 1meg lin

get some tag strip stick the pot in the ground switch hole and away you go!...

Enough space in the 5e3 chassis to fit it...

springhead

Seconded on the VVR. Works a treat in my 5E3.  

BahHumbug

Thanks for the suggestion chaps.  I'll bear that in mind.  As it happens I already have a simple resistive attenuator built to go in this, but I guess the VVR will be considerably more flexible.  TBH, I suspect it'll end up being a future mod, as I'm fairly focussed on getting it to a state of finishedness right now.

poopot

The vvr will save your valves as well

surfguy13

Hi Duncan

Really am delighted that the P12Q has worked out so well for you in the 5E3.  I knew that it would be a huge improvement on the V30. 

The project looks like it is really motoring so look forward to seeing how it progresses.  Good luck!!!  

Guy

BahHumbug

Calling @poopot and/or @springhead, or anyone else who knows.

I'm just looking at this VVR circuit - from the point of view of understanding it, how it works, where the bits go, what to connect to etc.
It looks obvious, but I'm going to ask just to be sure.  The input (B+) comes directly from pin 8 of the rectifier valve.  The output goes to the junction of the first filter cap and stepping down resistor (B+1) via the wire that was previously connected to pin 8 of the rectifier valve.

Am I right?

TIA

springhead

Yes that's right, that'll work.  If you wish you can add another R/C filter stage prior to it.  If you have any hum issues that might be worth a go.

Most important thing is to make sure the mosfet metal tab is isolated from the chassis.  The tab is at B+ !  they come with mounting kits - rubberised rectangular thing, plastic ferrules to go in the hole etc.  Check for continuity between the tab and the chassis before first power up.

poopot

Yep... exactly what springhead said.

BahHumbug

springhead said:

Most important thing is to make sure the mosfet metal tab is isolated from the chassis.  The tab is at B+ !  they come with mounting kits - rubberised rectangular thing, plastic ferrules to go in the hole etc.  Check for continuity between the tab and the chassis before first power up.

Blimey.  Now thats good advice.  I am quite careful and think about things before doing, but I hadn't spotted that feature of the fet yet.  Thanks.

BahHumbug

Completion of the woodwork............

The carcass had its corners rounded off, and the baffle and rear panels got made:

https://www.dropbox.com/s/0hssvmnsggssdr0/P1060637.jpg?raw=1

Little holes were drilled, screws and screw cups were deployed and its all in one bit:

https://www.dropbox.com/s/4e6heuxw6e9iizi/P1060639.jpg?raw=1

https://www.dropbox.com/s/35bn5wnnn9v25tw/P1060640.jpg?raw=1

Resistive attenuator mounted in the bottom of the cab:

https://www.dropbox.com/s/0163djb5x8gtkgn/P1060638.jpg?raw=1

The carcass still needs a bit of hole-filling and cleaning up, but the next step is to think about covering it.  Its gonna be vinyl, not tweed, maybe blue.

VVR is under consideration.  I also have some smaller coupling caps waiting to go in, as I'd be interested to see what its like with its bottom end tamed a bit.

poopot

BahHumbug said:

springhead said:

Most important thing is to make sure the mosfet metal tab is isolated from the chassis.  The tab is at B+ !  they come with mounting kits - rubberised rectangular thing, plastic ferrules to go in the hole etc.  Check for continuity between the tab and the chassis before first power up.

Blimey.  Now thats good advice.  I am quite careful and think about things before doing, but I hadn't spotted that feature of the fet yet.  Thanks.

Don’t handle it without earthing yourself first either!.,,

BahHumbug

Since the flurry of cabinet building, there hasn't been much movement on the 5E3.  However, I'd been thinking about messing with the coupling caps (or maybe decoupling caps, I can never remember which is which) for a while and this morning I did just that.  Yes I know the 'flabby bottom end' is all part of the charm of the 5E3, but I didn't really like it, and where's the fun in not making it my own amp?
I'd read up on the subject some weeks ago and done some calculations of my own to figure out what values to try.  I've got a spreadsheet that models the input stage and allows me to generate a frequency response graph so I was able to plug in different values to that to see what difference it makes.  Anyway I found that numerically speaking you have to change the cap values quite a bit to make a noticeable difference to the bottom end response.  In the end I bought some 0.0047 and 0.0022 microfarad caps, which seems like a big change from the standard 0.1 microfarad.  I bought enough to do the post-input stage and post-phase inverter, although I decided to just start with the input stage and see how I felt about the difference.  I also decided to go with the 0.0047 microfarads first.
It was well worth trying and just doing the post-input stage was all that I needed.  The flabby bottom end is gone and, as you might imagine the amp is much cleaner much further up the volume pot.  The drive, when you get it, is nice and quite bright, none of the flub.
I must admit that this value of cap might actually be a bit much on the bright channel.  It really is quite bright, so might be worth trying a slightly bigger value.  Having said that, I prefer a mellower, more rounded sound.  As it turns out, the normal channel is pretty much bang on for my taste now.

Its still fecking loud though.  I am going to see about sorting out that VVR..........eventually.

BahHumbug

Crikey, time flies!  I've been meaning to do some updates for a bit.  Hadn't realised its well over a year since the last one.

The VVR got done in February this year.  The suggested FETs were either expensive, or difficult to find, so i used a STW12NK90Z instead (bought from Modulus, along with a the tag strip and a few other bits and bobs).  The spec looked like it should do the job.....and it did.  I did the rest of the circuit as per poopot's diagram above, and it works fine.  The FET didn't come with an insulator, but I found one on ebay for pennies.
Its definitely a nice little mod - great to be able to get the 5E3 overdrive at civilised volumes.  Nice

And then.....

BahHumbug

Also in February, I got around to covering the cabinet.  Now woodwork and soldering are things I can do in quite a relaxed way.  Sticking tolex to cabs is not.  Hence the photos of this process ran out at the measuring and cutting stage.

https://www.dropbox.com/s/cskvn8jws8kpcaq/Photo 16-01-2022, 16 19 57.jpg?raw=1

The end result isn't too bad.....from a distance....and please don't peer too closely at the corners

https://www.dropbox.com/s/ptpchay36szq7v7/Photo 20-02-2022, 10 03 37.jpg?raw=1

BahHumbug

So with the amp all in one piece and looking pretty (from a distance).  I took it for a run out at a band rehearsal.  Had some fun running a stereo setup with my other amp, a Cornell Romany.  The 5E3 worked fine, but......

Well I just wasn't happy with the sound.  When I first fired it up (a few years ago) it had been with a Vintage 30, and it was loud and not very nice.  The Jensen P12Q that went in later was an improvement, but I had to admit it still wasn't working for me.  The amp was noticeably mid-rangy and notes from the top couple of strings of the guitar sounded harsh.

I went through a period of tinkering, which was as much about trying things, reading and learning, as it was about fixing the sound.  I checked the resistance of all the resistors and did continuity and voltage checks around the whole circuit, just to make sure nothing was wildly out of spec.

I checked the power amp bias, and found that it was a bit hot - the tubes were running at about 118% of rated current  with the standard 250ohm cathode resistor.  So I ordered some resistors and tried a couple of different ones to cool the bias.  I wasn't able to detect much difference in the sound, but certainly got the plate current down.  It currently has a 470ohm in and running cool at about 60%.  I'll get around to warming it up a bit sometime.

I also added a 470k grid stopper on the input of the phase inverter.  This was recommended by Merlin Blencowe (www.valvewizard.co.uk) and I was quite curious to see that you can just throw a resistor in like that and it not make any difference to the sound (it doesn't).

Anyway, after all that faffing the amp was no different in terms of sound, so I did the thing that I'd been putting off.

BahHumbug

.....I changed the speaker again.

When I started the project I wasn't earning much so everything had to be low budget.  However in April '21 I started a new job, earning more, so I can be a bit more spendy now.

I had a look in the Fretboard classifieds and found that @fretfinder was selling a Celestion Blue.  I had heard plenty of folks gushing about these so bought it.  Had a nice morning's drive over to his place to pick it up.  Thanks again to Mr Fretfinder.

The blue transformed the amp.  Lovely warm bass and chiming top end, and the mid range is much more, er, tame.  Result.  Progress.

I had always intended to try the blue in my Cornell as well, so I did.  The stock speaker on these is a Jensen 12/70.  I hadn't any complaints about the amp, but, well you know.  The blue was less of a transformation to the Cornell, but definitely an improvement, so I left it in there and decided to commit to the speaker rabbit hole and buy another.  I didn't want to just get another blue, so after a bit of reading on the Celestion website decided on an Alnico gold.  I ordered a new one from Hotrox, along with some NOS Mullard 6V6GTs.

The gold also sounds great in the 5E3, so I'm going to leave speakers the way they are for a bit.  I might try swapping them over one day.

The Mullards are actually CV511s, which I think is a military spec 6V6GT equivalent.  Anyway, I couldn't hear much difference between them and the JJs that I had in the amp before.


So, I'm finally happy with the 5E3......

Having said that, I've really come to enjoy faffing with it and the associated learning that goes with that.  So I think there might be some mods in its future.......

benvall

I missed your thread first time around but I’ve just been through it. Good work, I love the tolex colour.

As someone who has had most of a JTM45 in bits for around 10 years, I’m glad it’s not just me who gets sidetracked with life. 

BahHumbug

benvall said:

I missed your thread first time around but I’ve just been through it. Good work, I love the tolex colour.

As someone who has had most of a JTM45 in bits for around 10 years, I’m glad it’s not just me who gets sidetracked with life. 

Thanks for your kind comments.  I’m really pleased with the tolex colour.  I consulted with some female friends before deciding on what colour to buy - I’m really bad at making aesthetic decisions for myself.

Yeah it’s a real pain when life gets in the way of important tinkering