Your posting and others like it are the reason that I read these forums.
Hill Plasmatronics speakers were built in my hometown and I could never have afforded a pair when they first came out. Mainly because I was only 12 years old and my paper route only paid a few dollars a month.
What a kick it was to see this posting today. Thank you for sharing and I'm bookmarking the posting.
Hill Plasmatronics speakers were built in my hometown and I could never have afforded a pair when they first came out. Mainly because I was only 12 years old and my paper route only paid a few dollars a month.
What a kick it was to see this posting today. Thank you for sharing and I'm bookmarking the posting.
The gas flow is ~1.25 cubic feet per hour - very low. It makes absolutely no noise.
The fan was needed because the tubes, power resistors, and plasma driver were all in close proximity. We used an AC fan and placed a resistor in series with it to slow it way down. My new system does not need it.
I had the rare opportunity to hear the plasmatronics speakers back in the late 70s at a stereo store in northern CA and I still remember the record that was playing - Return to Forever by Chick Corea. Being just a teenager, I didn't have the educated ear of most audiophiles, but I knew what good sound was having been around alot of high end studio quality audio recording gear myself. The treble of the plasma section was effortless and immediate. I was shocked at how loud they could play and how real everything sounded. There was no audible hiss or noise when no music was playing. As an electronics fan i was intrigued at how these things worked and ended up getting on the salesman's nerves asking all the questions I had. I have yet to hear such good treble to this day. Electrostats came close but couldn't match the dynamic range.
The need for helium is a huge deal breaker with this speaker technology. Its getting more and more expensive to buy helium and the quality of welding grade helium is all over the place regarding impurities. Medical grade helium is virtually unavailable to private customers and its getting more difficult to purchase it in general due to the medical and aerospace business having priority over the existing stock. When the feds released most of the strategic helium reserve, cost plummeted and use skyrocketed. Roughly 15 yrs ago they tightened down on the sale to party supply stores and private individuals. This made it hard to purchase smaller quantities of helium as most suppliers only provided the larger cylinders to their commercial customers on a lease or rental basis. Most private customers don't want that kind of cost obligation. The private owned 155 cu ft helium cylinders including the smaller 80 cu ft sizes were becoming harder to find due to the shortage imposed cutoff to private consumers. I used helium for various leak detection and science experiment purposes as well as for welding very thick aluminum. I just keep a small tank on hand and use it sparingly, so no more using for birthdays... i don't know how those dollar stores can afford to sell helium balloons for $1 a piece at the current going rate for helium.
Most of the cheap helium today comes from Russia and China. As with neodymium, they control prices which makes our speaker hobby more expensive and there's nothing we can do about it other than settling for ferrite magnet drivers. Its not that there's just a helium shortage in the US, but rather a shortage of the production itself. The oil companies control this commodity and as with oil itself, they control prices and the (lack of) production. As most helium comes from oil and gas wells, there's no way around that.
The need for helium is a huge deal breaker with this speaker technology. Its getting more and more expensive to buy helium and the quality of welding grade helium is all over the place regarding impurities. Medical grade helium is virtually unavailable to private customers and its getting more difficult to purchase it in general due to the medical and aerospace business having priority over the existing stock. When the feds released most of the strategic helium reserve, cost plummeted and use skyrocketed. Roughly 15 yrs ago they tightened down on the sale to party supply stores and private individuals. This made it hard to purchase smaller quantities of helium as most suppliers only provided the larger cylinders to their commercial customers on a lease or rental basis. Most private customers don't want that kind of cost obligation. The private owned 155 cu ft helium cylinders including the smaller 80 cu ft sizes were becoming harder to find due to the shortage imposed cutoff to private consumers. I used helium for various leak detection and science experiment purposes as well as for welding very thick aluminum. I just keep a small tank on hand and use it sparingly, so no more using for birthdays... i don't know how those dollar stores can afford to sell helium balloons for $1 a piece at the current going rate for helium.
Most of the cheap helium today comes from Russia and China. As with neodymium, they control prices which makes our speaker hobby more expensive and there's nothing we can do about it other than settling for ferrite magnet drivers. Its not that there's just a helium shortage in the US, but rather a shortage of the production itself. The oil companies control this commodity and as with oil itself, they control prices and the (lack of) production. As most helium comes from oil and gas wells, there's no way around that.
I can say with confidence that welding grade helium if absolutely fine for these speakers. Balloon grade comes from the same source, but those tanks are not purged and you get a cylinder with unknown history. Welding grade cylinders are pumped down and purged and have a guaranteed purity rating.