B15N style cab build FINISHED!

[rubis]

This idea started whilst on holiday a couple of weeks ago, with too much time on my hands to mull over new 'projects', and with easy access to alcohol and the internet, I decided I needed a B15, the perfect partner for the '64 style P bass I made recently. 

However, once again, without the spare cash to find and buy an original '64 Ampeg, I began to consider the alternatives, and in a bit of a deja-vu situation, the answer seemed to present itself. 

Last year, whilst on holiday I missed out on a great deal Kenny's Music had on the Ampeg PF20t and PF50t, basically because I dithered instead of snatching one, and they went out of stock by the time I got home and got my derrière in gear. So, this year when I noticed a similar offer on the PF20t from Gear4Music, I ordered one and delayed delivery till I got home. 

This will suit my needs perfectly, I have never had a valve bass amp before, it's low power, intended for home practice and recording and you can plug it directly into a recording interface, without a speaker connected. 

From what I read, the sound was reminiscent of a B15, and seemed to me to be the perfect alternative to shelling out on an original or a Heritage reissue, providing you can find one! 

Then I began to ponder on the idea of building a cab like the infamous 'double baffle' cab from the early B15 fliptop combo's. 

As you can imagine, there are a lot of references to the B15 on the internet, but surprisingly few people have properly documented any attempts at copying a cab or even restoring one, so getting anything more than the basic dimensions proved a bit tricky. 

I found exploded diagrams of the cab design and the baffles, and snippets of information from various sources, including an American company called Fliptop cabinets, who make reproduction cabs and restore original gear. 

I had a fair bit of the drawings I needed, and enough reference photo's to have a go at 'reverse engineering' a cab, which after all will not be a copy of a flip top, when up stepped the wonderful Chimike of this parish, with a kind offer of a complete set of plans for a B15N...…….result!

Thanks again Mike 

So, this is what I have in mind. 

As I mentioned, I don't want or need the flip top arrangement on the top of the cab, this cab will be used for home practice and recording, so an authentic sounding and airtight cab will be better suited to my needs. The amp will be used a lot of the time, plugged into my recording interface and utilising the Two Notes cab sim, which has Ampeg models on it. 

This will also (hopefully) make the cab build easier or more straightforward, as I have never made a cab before. 

On the Fliptops website they offer an extension cab, which is pretty much exactly what I have in mind, with a solid top instead of the rotating tray thing, no wheels dolly on the bottom, and with a removable back for access to the speaker, but still retaining the characteristic double baffle design.

 

I have a full sheet of 3/4" plywood, which is what the originals were made from, this has been in the cellar below the garage since we moved into our house 15 years ago, and it looks quite good quality and void free, just a bit dusty! 

I found a local seller on Ebay, selling an Eminence Delta 15a, which is the replacement speaker recommended by Fliptops for the cabs they make, which incidentally start at around $500 plus shipping and import tax, so, obviously are a non starter for me. The Eminence seemingly sounds the closest to the original speakers.

Anyway, got the speaker for £10 (bargain) and if anyone can find a use for the metal speaker grille and port tubes that came with it, drop me a line and I will gladly post them to you, as I won't need them. 

The grille cloth and the checked tolex is available, albeit not in the UK (unless anyone knows better 😉) and this will be the most expensive part of this project, which so far has cost me £10 and a gallon of diesel! 

If anyone is interested, I will slowly keep you posted! 

[rubis]

I've finally made a little bit of progress with this now.

I'm afraid I got off to a false start with the sheet of plywood I had found lying around, it looked sound enough, but the damp Devon climate had done it no favours and when I began to cut it up, it was unusable! 

So I got a couple of sheets of new ply 1220x606 which fit perfectly into the back of a saloon car and left little wastage!

I got started yesterday but I didn't get a chance to post the progress because me and the man cub went to the Pavillions to see The Pixies, who were brilliant, by the way!

So, I did the speaker baffle first, need to do the spacer blocks and mounting bolts, and then grille cloth

I have made the front facia thing, which is pretty much like a picture frame, it's busy gluing as we speak. My thinking behind doing that was, firstly it looked fairly easy to do, and most importantly, if I could get that fairly square, I could use it to help square up the sides of the cab when I glue it up. 

Then I cut the four sides, which are all the same size as this cab won't have the flip top arrangement. 

I don't have a dovetail jig, so I had intended to just do butt joints and add a square or triangular fillet strip to strengthen the joint, but then I found a clip on YouTube of this bloke who made a simple cheap jig for doing finger joints and thought it was exactly what I needed. 

Here's the clip 

Now, he used pine, both for the amp casing he made, and for the jig. 

I couldn't find 18mm pine, so I had to use MDF, and the cab is plywood, which had a tendency to split little bits of the surface layer with the router, but even so, I have to say, it worked rather well, and will make for a neater joint, I'm sure. 

Here's my MDF jig, not as tidy as pine and prone to splitting when the brackets were screwed on, but it did the job! 

I cut out the back panel and the inside baffle, which are just a couple of squares, and marked out the ports on the inside baffle.

I hope to glue the sides of the cab together this week and, assuming it goes well, I will try to route out the port slots and speaker hole while the glue is curing.

Edited September 15, 2019 by rubis

[rubis]

I've made a little bit more progress on this now.

I'm hampered by the weather as I have limited room to work on this in the garage at the moment, and I'm having to do it outside, in between the customary Devon rain. 

Anyway, the cab is glued, I found that using the front fascia part to help square it up made things a lot easier, otherwise I might have been experimenting with a rhombus shaped cab. 

Not being a cabinet maker by trade, there was a bit of filling and sanding needed around the joints, but it's smooth now and all that will be hidden under the tolex later.

The main thing is, it feels rigid, it looks about right and it's square! 

I also glued in the spacer bits, behind the front facia and the speaker mounting baffle glues in behind that next. 

[Maude]

Ooh I like the look of this. I'll be looking forward to future instalments. 👍

 

But, you are now responsible for my little brain working over time, and will be fully accountable for any silly decisions I make regarding my love of the Ashdown LB30 Drophead. 😁

[rubis]

If you'd like a set of plans just give me the wink 😉

[Richard R]

3 hours ago, rubis said:

I saw this, thought they were jump leads and wondered where the -ve connection was going. It's been a long week...

[rubis]

Got the speaker baffle done today, it went quite well, if not a bit noisey for a Sunday afternoon, what with all the routing involved! 

I need to drill the holes for the front baffle to locate and  hang, and I need to get some of those T-nut things for fitting the speaker, as that's what the bloke at Vintage Blue does, I thought I'd follow his example, he looks like he knows! 

http://vintage-blue.com/products.html

[rubis]

I'm trying to think ahead to things like cabinet fittings and wiring in the speaker. 

Now, the speaker socket on the side of the reproductions made by Fliptops and Vintage Blue are quite authentic and original looking, like this 

However, I can't find any that look like that in Europe, does anyone know of a good supplier of cabinet parts? 

I have a spare speaker cable lying around with nothing to do, and it's decent quality......Van Damme cable and Speakon connectors, so I could use that and fit a suitable Speakon socket...…….I'd have to put a jack plug on the amp end though) 

Or would I be better off going jack to jack and find a retro looking jack socket for the cab? 

Are Speakons better than jacks?

Any recommendations or advice would be most welcome.  

 

[orangepeelneil]

Hello, 

SpeakON's  have some benefits to jacks, obvious one being locking (won't accidentally pull out,) and  current rating , the connectors are harder to short out. plus I believe SpeakONs cables can have bigger conductors,

One option would be to use a Neutrik  NLJ2MD-H, which is a combined  SpeakON and  1/4" jack in the centre = then you could use a jack to jack or SpeakON to jack, not very retro looking though ! 

 

Thanks Neil 

Edited October 6, 2019 by orangepeelneil
spelling wrong!

[rubis]

Hi Neil 

                that's brilliant, thank you kindly for replying, I'm not very 'au fait' with all of this side of things, and I'm not very confident with anything to do with wiring or electronics. 

Thanks again 

                              Harry

[rubis]

Got a bit more progress to show on this today. I was a bit concerned about getting the speaker mounting bolts properly square so  that the speaker located easily. 

I opted to use M6 bolts mounted from the outside of the speaker baffle, into Tee nuts which are recessed into the speaker baffle, so that they don't come into contact with the grille baffle (hope that makes sense). Now, as I want to use eight of these bolts, rather than 4 long pointed bolts as on the original, this means they all have to be square to the baffle face, there would be less room for error because the M6 bolts are quite a snug fit through the 8 mounting holes on the speaker. 

I placed the speaker onto a scrap sheet of plywood and drilled holes through, to make a sort of fitting jig. 

Then I placed the speaker baffle over the top, lined the holes up and used this to help keep the bolts square whilst I hammered them into the recesses. 

I also put a bit of Loctite Threadlock on the top of the bolts, before tightening the Tee nut up into position, hoping to keep them from working loose, might be overkill but I had it available, so why not! 

The speaker baffle was then glued into place and clamped up, I also added 4 of the little gluing blocks on the inside, like the original ones and then went round with some blackboard paint and some sealant.

I will recheck the sealant tomorrow in proper daylight and go over any areas which need attention, as the light was fading when I did it. 

Anyway, the process seems to have worked, as the speaker plopped straight into place on the mounting bolts. 

Next jobs will be the back panel and the speaker grille. 

[bertbass]

You could have tried these.  https://modulusamplification.com/Fender-Speaker-Mounting-Screws-Mount-Screws-each-P5875267.aspx

[rubis]

8 hours ago, bertbass said:

You could have tried these.  https://modulusamplification.com/Fender-Speaker-Mounting-Screws-Mount-Screws-each-P5875267.aspx

Had I known about them I would have! 

[rubis]

A bit of guidance and advice is needed now, if anyone wouldn't mind answering a couple of questions please, as electronics is not one of my strong points. 

I had a speaker cable lying around unemployed, and it's decent quality, so it seemed a shame not to use it for this rig. 

The problem is that it's got Speakon plugs at each end, and the PF20t has jack plugs for speaker outs. 

The cable looks to be 2 core, I can see a blue and a red wire inside the plug. 

So, I got a Neutrik jack plug, and assumed that I can just cut one of the Speakon plugs off, and weld 😖  solder the jack in its place, but the question is - does it matter which way round the red and blue wires go onto the jack. 

I assume the two cores are to be soldered to A and B in the photo above, but is A red or blue? 

 

Second question, if I may! 

I couldn't find the same kind of speaker socket that Ampeg use on their cabs, but I'm not at all bothered about that to be honest, because I found a nice retro looking Neutrik socket. 

Now, same kind of question, really, the speaker has two wires, one marked + and one marked - 

On the back of the Neutrik socket there are 4 poles which are marked 1+, 1-, 2+ and 2-

So again, which pole would the + wire from the speaker go to, and which pole would the -wire go to? 

Once more, thanks in advance for any advice 

Edited November 5, 2019 by rubis

[orangepeelneil]

Hello,

Yes speakons have four connections, you only need two.

I cannot see on the pics, but for speakon connections/cable  red is likely to be 1+ (hot/positive +) and blue 1- (cold/negative -)

On the jack from amp A  (tip) is + and B (ring) to -  

Just ensure your amp jack connects to your speaker + and -  (via speakons ) the right way round else to avoid incorrect phase. 

Hope that makes sense Zzzzz must sleep

[orangepeelneil]

[rubis]

Fantastic

Thank you very kindly orangepeelneil 

[basstone]

which wire you connect to + or -  will in practice only really matter if you connect more than one cab up to the amp. If you do connect 2 cabs together and mysteriously loose loads of bottom end then you will know the speakers are out of phase. Although most “vintage” amps and cabs used TS 1/4” jacks for speaker connections, I’m not a great fan as it is possible with metal bodied jack socket designs to short out the amp output whilst inserting / removing the jack with the amp switched on..

[rubis]

A little bit further forward with this now! 

I finished off the front baffle, using good old McDonald's coffee stirrers as a spacer around the inside of the cab front

Then put the bolts in and the wooden spacers on the back

A quick coat of my favourite blackboard paint and I now just need to source some grille cloth, and it looks like I will have to get it from the US, I can't find any in Europe. 

[rubis]

I routed out a recess on the side for the speaker lead

Then I wrapped a load of masking tape around the socket to make a sort of border around it, to allow for the thickness of the tolex

The I dropped it in place and filled in around it with wood filler. I'd like to say removing it went swimmingly, but that would be a lie. It took a couple of attempts because it kept pulling some of the filler away with it when I removed it, but I got there eventually. 

[rubis]

Now it's time to apply the tolex.

I managed to get this very reasonably priced on Ebay from a bloke in Germany who had some left over at the end of a renovation on a vintage cab, avoiding having to order it from the US and the additional costs involved. 

It actually looks dark blue in natural light, but this doesn't show up so much in photos. Looks  very cool though!

I have never tolexed anything before, so I am busy Youtubing before I dive in!

[EBS_freak]

This is look great!

[rubis]

2 hours ago, EBS_freak said:

This is look great!

That's very kind, thank you 

[rubis]

I must admit putting on the tolex was the part I was dreading, I have never done it before and, with good reason, I wasn't relishing the challenge of getting a reasonable result. 

I once tiled a kitchen floor with those brick sized tiles and although I had marked out datum lines, they didn.t quite lie parallel with the kitchen units, and your eye was drawn to it, to the point where I had to take them up and start again..(we're all a bit OCD aren't we?...……..please agree!!!!) 

Anyway, the checkered pattern on this tolex was a nightmare to get in line with the edges of the cab, and the problem is, you can't lie it down and then slide it about till it looks right, once the surfaces have glue on them the bloody stuff sticks like stinky poo to a carpet! 

I used a couple of strips of masking tape to make the lines more visible and with a LOT of trial and error got it looking square all round. 

I started at the top and worked around to the bottom, so that the joint would be at the bottom, out of sight. Once I got started it all went better than I was expecting and I actually enjoyed doing it. I should think doing a cab with ordinary grained tolex would be a bit easier, as you wouldn't be concerned about keeping the squares in line.

I used a heat gun to soften it up around the recessed plug socket and then loosely screwed it into place to hold it down

Got to clean the excess glue up a bit and then fit the corner pieces and a couple of nice leather handles on the top.

Today I will try to get the back panel done, it's just a flat square panel, and then stick on the spongey sealing strip.

[Si600]

Very nice. And yes, we're all a little OCD when tiling lines don't quite work.