This is one of four I purchased on eBay. As far as I can tell, units like these were manufactured as early as 1956 and I’m guessing all of mine are considerably newer. The DC resistance measures 6.5 ohms and the impedance is 8 ohms. The others all have very similar DC resistance ( 6 to 7 ohms) and are 8 ohm impedance. If you look closely around the edge, you’ll see a Philips head screw and three dark red circles. The red circles are the highly coveted JBL wax seals. If you can find an 075 with all four seals in place I understand they become considerably more collectable. All of mine sound great, and I’m using two at the present time.
One thing I’m not good at is determining the proper value of conponents for a crossover network. I do know that inserting a capacitor in series between an amplifier and a speaker will reduce the level of low frequencies reaching the speaker. With that in mind, I have decided to use a value of 2 microfarads, non electrolytic, 250 volts for a crossover capacitor. The 075′s sit atop and are connected to a pair of older Pioneer CS-63 speaker systems. By the way, I replaced The stock Pioneer 15-inch woofers with Electro-Voice DL-15′s. These are rated at 400 watts and have 2.5 inch voice coils. By now, some of you may be cringing, but I think these speakers sound and work quite well. I’m sure no damaging low frequency energy is getting to the 075′s. My amplifier has less than 30 watts per channel and I always use a compressor ( Alesis NanoCompressor ) between my source signal and amplifier to prevent any peak level from getting to the speakers. I sense after listening to alot of different sounds and especially cat hissing that my crossover is well above the suggested frequency of 2.5 kilohertz. From what I’ve read online, alot of audiophiles prefer a higher crossover on these tweeters for a “sweeter” sound. Please listen and enjoy “Hissing Very Loud” on this site. I think you just might know by now what speakers I connected when that recording was made.