rubis

Thank you very kindly Phil, praise indeed from a man who knows about these things

Yes, I think that's a fair assumption

Here is a diagram from one of the early brochures or sales literature, it seems to me as if the various parts act together, to get the desired effect. I also found this description, which explains it far more elegantly than I could! The first B-15s generally housed a Jensen P15N speaker, brilliantly set in Jess Oliver’s patented double-baffle design. The original design placed the speaker between two baffles with 15-inch ports, separated by ⅜ of an inch. The outer baffle had a 15-inch circular cut out and a bar across the center of the speaker cone. The speaker was mounted to the inner baffle, which was fixed to the cabinet. This inner baffle featured eight oblong ports (two above, two below, two on each side) that passed the speaker’s rear wave output through the ⅜ of an inch space and through the outer baffle’s 15-inch opening, where this rear wave meets with the front wave completely in-phase. Here's a link to the full article https://reverb.com/news/the-golden-age-of-the-ampeg-b-15-1960-1980 And here is a link to a portaflex thread on Talkbass, with more than enough information on the various versions of the design https://www.talkbass.com/wiki/technical-speaker-cabinet/#2-double-baffle-cabinet Hope this is helpful gents, but I must confess I don't completely understand the physics involved. I don't know whether it would work at higher volumes, the original B15's were, I think only about 25 watts, but I have read somewhere recently of folks using a PF20t or PF50t and then slaving it up with something like a Baby Sumo to get a 'turbocharged' B15! It's probably a good thing that I don't play in a band, as I'd be after something like that!

Thank you Stub Mandrel If you look at this photo of a pukka fliptop, taken from above with the lid removed. The innermost panel, with the slotted ports has the speaker attached to it. If you look at the circular speaker cut-out, you can see the gap between this panel, which on any other cab would be the solid, fixed front panel of a cube really. The difference with this cab is that it has another removable front panel, which has the speaker grille cloth attached to it, and is bolted to the inner panel. There are spacer blocks with bolts through them to keep the gap even all the way round. These two diagrams are like a cross section of the cab, as if it were cut in half horizontally. The turquoise part being the outside grille baffle/panel. Here's an exploded view of a whole fliptop cab. The cab I made is simpler, with a solid top and a removable back panel, quite conventional in that respect, but it's the same dimensions and has the same baffle arrangement. There is an American company called Fliptops who make replacement B15 cabs and also do an extension cab, just like the one I made. I have a proper set of dimensioned plans for this, if anyone wants a copy then please PM me.

What a stonking performance by all

Wow

Thank you for the interest, encouragement and help, without it this would have taken me far longer and not been half the fun. Here is a family photo with the Ampeg PF20t and the '64 style P bass I made this cab to partner up with, I think they're made for eachother.

Thank you kindly

Thank you very much Jus Lukin

I forgot to ask, one last question! I used these roundheaded cabinet nails to fix the corner pieces, I got them from Modulus, but they didn't have enough and their Email is crap, I can't find them anywhere else, anyone know where I can get these things? https://modulusamplification.com/Stud-Nail-Silver-Colour-for-metal-corners-Single-part-P1989503.aspx

Stevie I have a bit left over from this, it's about 150x140cm, you're welcome to it if you want it? PM me your address and I will post it to you.

Finally finished! There were just a few finishing off jobs to do, but for some reason it took a while to get them done. I took a bit of trouble to try to make it as airtight as possible, I've not made a cab, or even looked inside one, but from what I've read about this design, ownership is as much about chasing squeaks and rattles, as about enjoying the sound it makes! So, I got some adhesive spray, some sheets of black felt and foam, both about 1mm thick, and pinched a load of tricks from others, that will hopefully each make a little bit of difference. I glued rubber patches on the inside where the bolts for the handles come through. Then made one with a smaller diameter hole than the speaker socket, so that it stretched over and made an airtight seal. I glued a bit onto the spacer blocks on the back of the grille panel, as I have read these are a source of rattles. Then I followed the advice of Mark at Vintage Blue in the USA, I covered the other side with the black felt, it seems back in the day, they were covered with some sort of foam or similar, which was there to stop the grille cloth from rattling against the outer baffle. These would disintegrate over time and the cloth would flap against the front of the cab. Then I glued the wool felt to the inside of the cab, oh what sticky hairy fun that was! Then once again, following Mark's example, stapled on the grille cloth and heated it up in the oven to tighten it up onto the baffle, and bugger me it worked! This was quite satisfying! On went the back panel, and that was it!

That is fabulous

Both consummate professionals, fantastic to watch both clips

I've been having a bit of fun with a logo for the front of this cab, but first let me explain how the name Rubis came about. When I began my first guitar build a few years ago now, our two kids (now teenagers) were just toddlers really, and while they were 'helping' one day I said that we'd have to think of a name for our guitar company, and without hesitation the reply was Rubis…….their names are Ruby and Lewis, and so it seemed a perfectly sensible choice. So I was looking at the Ampeg script on the front of the B15 cabs and thought I could play around with it. I got one of these on Ebay, they're made of plastic and perfect for messing with I then began chopping and filing to try to make it say Rubis. The only problem I had was making a convincing letter 's'. I tried cutting a little sliver of the chrome effect finish to fill in a gap that shouldn't be there, but it didn't look right. So in the end, we decided to leave the repair out, it looks neater without it, not perfect, but better.

The best live video I've seen

Thank you kindly folks, I got some of the wool felt underlay stuff on the way home from work today. It looks just like the stuff Christine recommended above (thanks again) I think I will fart (probably the wrong word) about with it, holding it in place with double sided tape, until it sounds right, as per the advice above, and then use up the spray glue I have left from telexing for a more permanent job.

If you do decide to go for chambering, here is an idea of how Warmoth do it, with a kind of honeycombe-looking thing which you may be able to do with a forstner bit in a pin drill, and avoid nasty routers! Given the larger scratchplate on a 51(ish) p bass, it might work well. I've done chambering before, and it is effective, but I have only done it where a top has been glued over the chambers. I did it on an Ash and Wenge 'Blingray' build a while ago, it did cut the weight down quite a bit, but all the photos have gone from the thread, so not much help there, sorry! https://www.warmoth.com/ordering/chamberedbody30dayguarantee.aspx

Very good points

Here is a link to a 51 p bass build on the TDPRI site, they mention a bloke called Preeb, who has done some extraordinary builds, both basses and guitars, he is fastidious to say the least with his research. I think you would find all the information you need on there. There is also a link on that thread to a PDF named "P bass comparison" which is an accurate outline plan for the body shape, if you don't already have one. There are lots of other plans for things like headstocks and pickguards if you need them, not sure how much you plan to do yourself. Great project though, keep us all posted with it please, and best of luck https://www.tdpri.com/threads/51-p-bass-build-looking-for-info.187396/

I hope someone will correct me if I'm wrong, but the body is around 42mm thick Having said that, I just looked at the ones on the Warmoth website, and they are 1 3/4" which is about 44mm or 45mm. Anything in that area would be fine, I don't suppose anyone is going to take a set of calipers to it! More important, is that it balances well and doesn't feel like a millstone around your neck

Thank you very kindly Christine, I will look for some of this stuff tomorrow

I am in the process of making as sure as I can that there will be no leaks or rattles on this cab, an I have another advice question for you all please. What would you recommend to use for lining the inside of the cabinet? I have four squares of egg-box style foam lying around that I was going to use on a guitar cab, so I tried that in there, but I think it's a bit too thick. It will lie very close to the slotted holes on the front baffle, and I worry that they would not be able to function as they are intended to. I then thought I could cut up to completely cover the back panel, and use something thinner an less obtrusive on the sides? Is there any kind of best practice involved with lining cabs? What's the best stuff to use?

Yes, I quite agree, his attitude reminded me of Wilco Johnson when faced with similar prognosis, and I greatly respect his mettle. I really hope he shares some of Wilco's luck, and has a new lease of life. I notice, whenever his name, or that of Budgie, crops up in these pages, he commands a lot of respect