Description

Jensen H510 This listing is for a RESTORED and reconed 1953 Jensen H-510-ST-828 C5412 15" Coaxial of 16 ohms impedance and rated at 25 watts. Costing $135 when released ($1551 when adjusted for inflation in 2024), these coaxials are highly coveted, even today. First released in 1949, Jensen advertised the H-510 as the first-ever speaker to incorporate an acoustic lens for wide dispersion of high frequencies from the horn tweeter. The H-510 is still considered one of the best coaxials Jensen ever made. After our restoration, it certainly was well worth the time and effort! Some of the ads Jensen released in 1949 actually show the acoustic lens plates with an incorrect order! The correct configuration should have the larger diameter lens plate on the front-most position. This allows for a line-of-sight to the first grill when viewing from a side angle. We've listened to the speaker with both configurations and can attest that the proper configuration indeed makes vocals and instruments sound seamless and more real, with a significantly less "pinched"/"nasal" quality. The H-510 has a punchy and faithful sounding 15" all-paper cone woofer and a red colored phenolic dome tweeter, both drivers utilizing Alnico 5 magnets! For those not familiar with the extras that come with these speaker, the basket of the woofer has pre-drilled locations for three trapezoidal shaped plates. From the factory, every H-510 came with a standard speaker terminal plate. Mounted on this terminal plate is a crossover/filter for the tweeter (according to Jensen, the "H" series coaxials has the tweeters filtered at 2000Hz), screw terminals for fastening standard speaker wire (16 ohms impedance here), and two octal-style sockets for optional accessories. For standard 16 ohm connection to an amplifier, use screw terminals "1" (negative) and screw terminal "3" (positive). The two octal-style sockets for two optional accessories (not included nor required) are for the following: 1) a Control Network with two L-pads for greater control with balancing the tweeter level 2) an Impedance-Adjusting Transformer Assembly which presents 4/8 ohm, 500-600/250 ohms, or 10k/5k ohms impedance to the amplifier (depending whether you use model T-101, T-102, or T-103, respectively). You can use this H-510 coaxial, however, without these optional accessories. It's currently ready to play as a standard speaker by using the factory-supplied bypass plugs (installed in each socket). The Control Network bypass plug is indexed to only be inserted one way, so it isn't possible to accidentally insert it incorrectly. The Transformer bypass plug is a standard octal pin configuration, however, so you need to make sure the numbered pins on both the plug and socket match up if you do remove it later for cleaning. This coaxial involves a soft connection between the cone and the horn. There is a felt ring that connects the front of the woofer cone to the back side of the metal horn. There's a lip edge on the rear of the horn specially made for this application. The horn is then threaded into the woofer's magnet assembly. On the back of the woofer magnet is the tweeter, and it mates to the woofer's magnet assembly via a paper gasket and bolts. The Restoration: The H-510 is an advanced speaker in terms of sourcing the right parts, cleaning, prepping, and reconing the speaker. It takes more patience to restore a Jensen coaxial than other speakers. In addition, the felt ring and tweeter gasket are not off-the-shelf parts, so they have to be custom made. We fortunately used our laser to laser-cut a new felt ring and a new fiber gasket, just like the originals! Each step of the way, every part of the speaker was cleaned. There were some fiber washers that deteriorated on some of the lugs on the basket, so we laser-cut some new ones since those, too, aren't obtainable via any modern replacements (at least not the same exact diameter as the originals). The first line of action when reconing a speaker like this is finding the cone and the 2" kraft paper voicecoil - not an easy part to find at all. You usually have to custom make a voicecoil like this, because you won't find a NOS one to replace it, nor will you find a newly manufactured paper/lacquer one a la 1950's style. Luckily, the original voicecoil was still good and usable since it separated easily from the original cracked/torn cone. There was obviously some structural degradation to the collar of the voicecoil (some separated layers of paper that came off with the cone and old adhesive), but that wasn't a problem. To remedy this, we needed to reinforce the top of the voicecoil former for a solid attachment point to the cone throat. We measured out an exact sized strip of a special paper, carefully impregnated it with a specific epoxy for this application, and adhered the new collar to the voicecoil former with huge success. A very thin application of epoxy was also applied to the bottom edge of the voicecoil former, just where the bottom of the windings meet. This ensures that the enamel wire will not become unwound in case the original lacquer did not hold up during use. Ultimately, the geometry of the voicecoil was unaffected during this time of additional handling, and it fortunately remained perfectly round, moving freely in the voicecoil gap without any alignment issues or rubbing! It's rare to be able to preserve an original voicecoil when doing a vintage recone. It's even more extraordinary that such a rare gem like a Jensen H-510 would even allow for us to reuse the original voicecoil! A lot of the character of the original speaker does originate from the voicecoil former material, number of winds (overhung vs underhung), some other secrets, etc, and you normally have to closely study these details to make a replica. Custom winding machine mandrels, the right enamel wire, the right paper, the appropriate epoxy for the power handling, etc... If it did require a custom one, we still would have built it nonetheless, because this speaker is well worth it. We reused the black cotton push-back insulation that Jensen put around the Litz tinsel wires. This is a significant detail tonally, and it also keeps the flexible wire in pristine condition, away from the elements! Manufactures of speakers today should be using this old trick! In early speakers (starting with field coil speakers), Jensen used voicecoil centering rings around the spider, as they allowed the user to tweak the position and geometry of the voicecoil after the speaker was fully assembled (via 2 bolts being loosened, a tweak performed, then the bolts tightened). In the case of this H-510, the original spider was glued/fixed to the frame and a 3-bolt base ring fastened to the frame, almost touching the outside of the spider. The H-510 doesn't come with a 2-bolt centering plate which is necessary for adjusting the voicecoil alignment. Therefore, the factory-supplied 3-bolt base ring was simply a cosmetic addition here. This was possibly an older basket design from a different model of speakers which did utilize such a centering system. Perhaps Jensen decided to "finish" the 3 threaded holes in the baskets with the trim rings for tradition. Finding a replacement spider with the exact same dimensions is difficult, and if the diameter is just a tiny bit too large, then the metal centering base ring will make contact with the sidewall of the spider, creating undesirable noises during excursion. The spider is best installed without anything touching the sidewall. We decided that the centering ring should not be reinstalled, but we are including it with the speaker. In choosing the soft parts when reconing a speaker, the compliance of the replacement spider needs to match the original. In this case, it's a medium-soft compliance. A replacement spider was chosen that most closely matches the outer diameter, height, weight, and number of ribs as the original. Using the measurements obtained by the original cone/VC/spider assembly, we were able to exactly replicate the way the voicecoil is indexed within the magnetic gap. This alignment is important in achieving the vintage tonal character of the original H-510. The condition of the original cone is the main reason most vintage speakers become candidates for a recone project. This H-510 is just about 72 years old, and the cone was very brittle. The previous owner had attempted some pretty nasty repairs with straight wood glue (!!!), turning the cone into more of a midrange. All of the pics we've seen of other H-510 speakers online evidence cones with age-related cracks around the surrounds and anywhere on the cone. These are lightweight cones for sure, and the original cone material just wont last - if you are planning to buy a vintage H-510, it needs reconing (and all the replacement parts sourced or custom-made)! That makes usable H-510's extremely rare! Sourcing vintage style all-paper, pressed 15" cones is already a difficult journey, and finding one with a ribbed spacing like the original is even harder. After lots of searching, we finally found a close match, with the ribs focused mostly towards the cone throat, and a smooth section near the surround. The surround profile and the cone weight was close to the original. The original bumper gasket could not be preserved, as it was made of a very crumbly, coarse fiberboard type material. It also seemed to contain some nasty chemical, as it caused a dermatalogical reaction when touched, similar to the way MDF acts, but worse. We have seen pics of this speaker and other models online which have the same type of bumper gasket, and many times there will be missing sections. We opted to use a better quality modern replacement that will last much longer. The Wiring: At first glance, the lacquer coated cloth wire looks almost like the cloth wire that came out later (irradiated PVC with lacquered cloth), but this wire is different. It has less lacquer than usual, and it has a silk spiral wrap around the multi-strand tinned copper. Generally, we like to leave vintage wiring intact, but since the owner of this speaker is going to expect detailed and holographic audio coming from the unit, we wanted to make sure that the result of all this work was going to be worth it to the ears. We auditioned the speaker using the original wiring and heard some artifacts that distracted from the original recordings. The highs were a bit grainy, slightly harsh and sibilant, and the highs didn't match the bass in terms of cohesion. Having tuned/built numerous speakers and amps, we know that some of the artifacts we heard are caused by the number of strands of wire, and others caused by wire direction (as every wire does have a tonal direction). The wire Jensen used in this speaker would be better suited for musical instrument duty (guitar, amp, etc) rather than hi-fi where we want the most transparency. To achieve the greatest degree of detail, imaging, and realism, we opted to replace the accessibly replaceable wire with directional, long-grain, oxygen-free copper - by far our most favorite wire. We paid special attention to the direction of signal flow here, and it paid off. The result was a speaker that sounded incredible: female and male vocals sound like they're really there. You can hear chest and throat resonances as real as they can be. Piano and stringed instruments are very real sounding. Electric guitar has so much vibe and expression. What's most notable is how everything has a nice punch/pop to it. The cohesion between the woofer and tweeter is spot-on. The attacks across the entire frequency range are so much better aligned with the improved wire. This speaker is very revealing now, so be sure you listen to the speaker wire inside and outside the cabinet or wall you install this (listen to both directions before installation, as this speaker will very clearly show you the right sounding orientation). We took a small demo of what the speaker sounds like in a TL-606 cabinet with the ports closed up (so the cabinet is basically sealed). It sounded more balanced that way, but the speaker does produce more fully and effortlessly with a much larger enclosure. Jensen recommended their 15" coaxials be installed in their Customode Type "M" Reproducer Cabinet. Such cabinet is a bass-reflex cabinet that's somewhere between 8.25-8.5 cubic feet of volume after subtracting the driver and other internals. We feel that this speaker would work well in an infinite baffle application. The speaker really wants room to breathe, but it loves a large baffle. In our demo, even though the cabinet used is not optimal, you can still hear how punchy the drums and bass are, and also how realistic the vocals are. This would make an excellent center channel for very realistic dialogue tracks. The H-510 was the single standard speaker in Fisher's Coronet R-3 mono tube console, produced between 1951 and 1955. If you are restoring one of those consoles or are in need of a restored vintage speaker that will last several decades or more, you've found it! We are including the original wire along with the original cone, spider, spider trim base ring, and felt ring. During our research, we came across several very cool advertisements and literature referencing the H-510. We will include printed copies of these! We are confident you will enjoy this speaker for many years to come! It has been painstakingly restored and tuned, ready to be housed on a nice big baffle somewhere. We were impressed how nice and cohesive the speaker sounded just after the fresh recone. We can't imagine how much more effortless it will become as it breaks in with play-time! SHIPPING This coaxial driver will be professionally double-boxed and packed with ample compressed kraft paper packing material in-between the inner and outer boxes. We will ship within 1 business day of payment via UPS or FedEx. Questions? Please message us and we will respond promptly.