Stromberg-Carlson? Anyone?

[dyche01]

Okay, so I finally decided to build a monophonic system around this SC amp. The deciding factor was finding a beautiful old Jensen co-axial, two-way driver on Craigslist. I bought the driver yesterday and picked it up from a very charming vintage audio enthusiast in The Mission District.



The crossover network is built into the base of the speaker, and is probably accessible by removing the phillips-head screw in the base. I haven't checked out the capacitors yet but it sounds pretty good as is. The paper cone was in amazingly good shape, with only one serious ding, which turned out not to go all the way through the paper. I repaired the ding and doped the cone with a 60:40 mixture of Elmer's glue and water. I got this formula from the old Spica-50 loudspeakers and used it previously on the passive radiators of my old Polk Monitor 7's (http://audiokarma.org/forums/index.php?threads/original-polk-monitor-7.589908/page-2).



I know I risked changing the sound (especially the bass) of these speakers, but the sixty-year-old cone seemed so fragile that I thought it was worth the risk. After the dopant dried completely the surface of the cone felt stiffer and less felt-y. When hooked up to my old Fisher, the driver didn't sound any different, so I am declaring victory.

 

[dyche01]

I also started building a cabinet right away for my new toy. Fortunately (or maybe unfortunately) I had enough scrap material lying around the basement to do the entire job. I started with a couple of rectangular forms (originally used as jigs to square up an oak stereo rack while the glue dried) and a piece of 5/8" plywood. I decided to wing the dimensions since I don't know any of the acoustic parameters of this Jensen driver anyway. I figure I can fix any significant problems after the fact.



The finished cabinet has a 1.6 cu-ft internal volume and is heavy as hell. I started prettying it up with a roll of walnut veneer left over from remodeling the kitchen.


I haven't thought about a grill yet but the driver looks pretty good naked, mounted in a piece of oak plywood. You might not be able to see it in the photograph but the flange is held by a 'gasket' made from adhesive-backed, cork shelf liner.



Finally, this project provides a great opportunity to use something I picked up at a junk store in Berkeley, like 15 years ago: a brass (or possibly copper?) horn from some ancient speaker system. It looks very old-school and would make a kick-ass reflex port.

 

[gadget73]

That thing was probably operated in an open baffle type arrangement anyway. If it gets funny, just pull the back off and let it go. Thats a very similar looking driver to the factory one in my EH Scott 800B. That thing has better LF response than you'd probably expect, and its in a big open cabinet.

 

[dyche01]

That thing was probably operated in an open baffle type arrangement anyway. If it gets funny, just pull the back off and let it go. Thats a very similar looking driver to the factory one in my EH Scott 800B. That thing has better LF response than you'd probably expect, and its in a big open cabinet.

That's good to hear.

 

[Pio1980]

Those S-C turntables were interesting. The PerfecTempo is the one I'm thinking of. Kind of a predecessor in design to the AR and Thorens type spring suspended units.

Mitch Cotter designed the Perfectempo for SC, the predecessor of all 3 point suspension belt drive turntables. Edgar Villchur perfected the concept with the AR XA.

 

[kve777]

That thing was probably operated in an open baffle type arrangement anyway. If it gets funny, just pull the back off and let it go. Thats a very similar looking driver to the factory one in my EH Scott 800B. That thing has better LF response than you'd probably expect, and its in a big open cabinet.

While the tools are out, I'd make a 3/4 size back panel to try if the driver doesn't like a closed box. It will allow it to breathe without looking unfinished.

 

[hunter00]

Those old drivers benefit from a bass reflex port in the front baffle when installed in a sealed box.May want to supliment the top end with an added compression horn,married together they would sound great.I will be driving vintage co-axials {Stephens} with my SC ap55 mono block..there getting close to finished on the bebuild

hunter

 

[dyche01]

Those old drivers benefit from a bass reflex port in the front baffle when installed in a sealed box.May want to supliment the top end with an added compression horn,married together they would sound great.I will be driving vintage co-axials {Stephens} with my SC ap55 mono block..there getting close to finished on the bebuild

hunter

Yeah, like I said, I will use the old brass horn as a reflex port, probably coming out of the top (or the bottom if I end up adding legs). I was reassured to discover that the dimensions of the horn (dia: 2.5-5.25", len: 10.5") are close to those of the reflex port in the cabinet that originally housed this driver (3" x 10").

In other news, I finished the veneer and started on the finish. I applied one coat of wipe-on polyurethane and the walnut is already starting to glow. It might end up sounding like crap but at least it will look classy.

 

[hunter00]

Heres a pair of 15 inch stephens and jbl horns I installed into a pair of cabinets..I like to offset the main driver to the top half of the cabinet,port in the bottom and a mirror imaged horn top corners...these sound deadly..
The second pic is a pair of my homemade jobs in smaller cabinets with 12 inch Stephens triaxials I put together...



hunter

 

[dyche01]

Heres a pair of 15 inch stephens and jbl horns I installed into a pair of cabinets..I like to offset the main driver to the top half of the cabinet,port in the bottom and a mirror imaged horn top corners...these sound deadly..
The second pic is a pair of my homemade jobs in smaller cabinets with 12 inch Stephens triaxials I put together...



hunter

Those are beautiful, especially the first pic of the cabinets with the 15" stephens drivers.

I am a little concerned, however, by the proximity of the Stag aftershave and Kahlua bottles. What kind of cocktails are you guys mixing up there in BC?

 

[hunter00]

Hahahaha..Good one!The theme in my mancave is primarily 50's /60's.Ive got the entire basement as one huge room equipted with a 5x 10 pooltable and its populated with old posters/bottles/vintage furniture and animal parts,antlers and mounts as I'm a hunter as well..lol,Have 3 complete matching 50'60's tube systems with period correct speakers to match...I'm not eccentric..really

hunter

 

[dyche01]

Still working on the speaker (more on that later) but I finally fired up the Stromberg Carlson AR-415 and gave it a listen. The pots were dirty and scratchy (no surprise) but, after a bit of Deoxit, it sounded really really good running through an old Polk Monitor 5. It sounded so good, in fact, that for once I am not really tempted to do much recapping. I popped the bottom and and found a bunch of yellow Astron film capacitors but no leaky old wax electrolytics. And the electrolytics in the cans seem to be in pretty good shape, so for the moment I am happy to leave well enough alone.

 

[gadget73]

I wouldn't necessarily trust those to be film. There are a lot of plastic cased paper capacitors from that time period. THey are not much better than the wax ones. Unless you have a high voltage cap tester to verify they aren't leaky, I'd change them.

 

[dyche01]

Dang, you might be right. They looked like film to me but I cannot find a definitive answer on the internets.

I am still gonna leave them alone for now.

 

[jaymanaa]

IIRC the 333 is a 433 without the phono section, which is just as well as the phono section on the 433 begs for an outboard unit. IMHO

 

[dyche01]

Um. Okay.

Cool.

 

[dyche01]

Here is a closer view of the yellow Astron caps.

Can anybody verify whether these caps are plastic-coated paper/oil or polyester film?

 

[gadget73]

The seam in the plastic shell is usually something I've seen with paper caps. Looks like a mold part line for the plastic over-molding.

 

[dyche01]

Cool. That's a good 'distinguishing mark' to know about.

 

[dyche01]

Okay, so I finally finished the speaker project, which took way more time than I anticipated. To refresh your memory, I bought an old Jensen K210 coaxial, two-way driver to pair with a Stromberg-Carlson AR-415 amplifier. I suppose I could have mounted the driver on an open baffle but I decided to use some scrap materials that were otherwise cluttering up the basement to build a proper cabinet. Initially I had some crazy ideas, including using an old brass horn as a bass reflex port. However, after reading the very helpful posts of gadget73, kve777, and hunter00 and digging through the literature on these old Jensen drivers, I realized that this was a bad idea. Apparently the mechanical Q factors of these drivers are too high for them to be used in either sealed cabinet or bass reflex cabinets with a tuned port. As noted above, they are designed to be mounted on open baffles or 'vented' cabinets, with large vent holes.

The guy I bought this driver from said it came from an Jensen-branded cabinet with a 3" x 10" port. I initially interpreted this to mean a 3"-diameter tube that was 10" long but, eventually, he set me straight and told me that the original cabinet actually had a 3" x 10" rectangular vent hole.

So, I remade the face plate for my cabinet with a similarly sized rectangular vent.



I covered the vent hole with some heavy, wide-mesh, structural fabric and mounted the driver to the inside surface with machine screws. Other than the driver, the only piece of hardware I actually bought for the entire project was a pair of knurled nuts and a couple of 10-32 pan-head machine screws to make binding posts for electrical connection.



Finally, I lined the cabinet with polyester batting to decrease some of the 'boxiness' of the sound and sealed everything up with drywall screws. The face is not so pretty, with all the screw heads showing, so I will eventually cover it with some of the wide-mesh fabric but, at least for now, I am calling it DONE.