Hii Tuyen
Yes the copper tubes first popularsied by a specialist UK company around 20 years ago. I also marketed these in a limited way around the same time with limited sucess and many returns due to breakage, hence why I stopped supplying them; your average joe soap did not heed the warning to not repeatedly bend them doooh! What it actually is, i.e. the original purpose is an RF connection for ships etc from the transmitter to the aerial. They usualy come in 1mtr and half metre lengths and powers up to 800w at rf freq.
For digital to DAC they are outstanding and can with some difficulty due to the rigid nature be coaxed into interconnects. The outer copper tube screens the inner core 100% and due to it's low resistance provides a very good earth return. They are a nominal 50 ohms impedance but the worst part is they use a steel inner solid core conductor with a silver or copper coating which can in an unsympathic system result in hardness. I really liked their speed and as you mention the quietness due to proper low resistance shielding.
The best use is between a transport and DAC (IMV) and they certainly unmuddle a lot of system, in an all horn system they may be too 'hard sounding', best try for yourself or borrow mine if I can find them!
The tube is available from Farnell and RS and others (see link). Only a few phono plugs are suitable for mounting due to having to solder the outer copper tube but there are some phonos where a grub screw can be driven in slightly and then secured by flowing solder over the 'joint'. The cable can be cut with a sharp stanley knife blade and then carefully through the PTFE down to the centre conductor. An iron of at least 25 watts will be needed and preferably twice this amount. I see since I last used this product they are now sheathing the SPC (steel) inner core(s) with copper then silver.
Having now checked up they come in several impedances down to 17Ohm and some websites quote the impedance per foot here;
Specifications for 25-ohm flexible coaxial cable (800W):
- Impedance: 25 ohms
- Type: Perfect for RF pallet (BLF578 800W)
- Diameter: 2.87mm
- Outer plating: Silver Plated Copper stranded wire
- Temperature range: -55C/+200C
- Dielectric: PTFE
- ROHS compliant: Yes
- Min inside bend radius: 2.8mm
- Max power handling: 600-650W(100MHz)
Specifications for Semi-flexible 50 ohm coaxial cable:
- Impedance: 50ohms
- Type: Perfect for RF pallet (BLF578 800W)
- Diameter: 3.51mm
- Velocity: 69.5%
- Capacitance: 96.8pF/m
- Outer plating: Bare, unjacketed, copper-tin composite 100% coverage
- Temperature range: -55C/+105C
- Dielectric: PTFE
- Inner conductor: Silver coated copper covered steel, ~1mm
- Attenuation: 26dB/100m at 500MHz
- ROHS compliant: Yes
- Min inside bend radius: 2.8mm
- Max power handling: >1000W(100MHz)
Link to useful site :
http://www.pcs-electronics.com/semirigid-25ohm-other-special-coaxial-cable-p-1275.htmlConnectors which allow a large 'bucket' for soldering found at Altronics, part No. P0241
It's far easier to change the bulkhead connector to a SMA type on the transport and use SMA connectors either end.
After all the empty, throw away piffle with the banned Mr. D, lets get back on track with some useful input.
V