In the early days of computers, before the IBM PC we (Motorola) used HP computer systems to control test equipment. The HP rep at the time always tied a knot in the line cord of every piece of equipment he was involved with during installation. I asked why, and he replied that it stops lightning from blowing stuff up.
Some years later I noticed a cable TV installer meticulously creating a small 3 or 4 turn loop in the cable drop right before the ground block, and securing it with cable ties. Again, I asked, and received the same reply, it stops lightning.
OK, we lived in Florida, the lightning capital of the US, but knots?????
Some research revealed, that yes, knots work. The dv/dt of a lightning bolt is on the order of megavolts per nanosecond, so I guess it doesn't take much inductance to convince the big spark to take a different path....sometimes.
RF is rather slow, so it's a bit harder to stop. I grew up about 2 blocks from a 10 KW AM radio station. It really sucks when the elevator music flows out of your DIY guitar amp louder than the guitar does. A small speaker with a diode across it played audibly when connected between the water pipe and the metal swing set in the back yard.
If the knot fits....don't mess with it!
Some years later I noticed a cable TV installer meticulously creating a small 3 or 4 turn loop in the cable drop right before the ground block, and securing it with cable ties. Again, I asked, and received the same reply, it stops lightning.
OK, we lived in Florida, the lightning capital of the US, but knots?????
Some research revealed, that yes, knots work. The dv/dt of a lightning bolt is on the order of megavolts per nanosecond, so I guess it doesn't take much inductance to convince the big spark to take a different path....sometimes.
RF is rather slow, so it's a bit harder to stop. I grew up about 2 blocks from a 10 KW AM radio station. It really sucks when the elevator music flows out of your DIY guitar amp louder than the guitar does. A small speaker with a diode across it played audibly when connected between the water pipe and the metal swing set in the back yard.
If the knot fits....don't mess with it!
When you think you have come up with something new, that has never been tried before... remember this quote from George.
Thanks Cal!
Nice to see that someone appreciates my ropy* attempts at humour.
Sometimes I tie myself in knots worrying that no one understands me! 😉
*adjective (British informal) very poor in quality
It only happened with "Westinghouse" Japanese 12SN7 tubes... USA or Canadian GE or RCA tubes (seemingly the same construction, but grey plates instead of black) didn't do it.
I use those exact tubes as driver in my monoblocs with no such issue 🙂
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Ropey* adj. Poor, or spoiled.
Adjective also used to describe bacterial infected fermentation, forming ropes of fluid when poured.
All sorts of pops and hums tonight - turns out one of my inter connect cables between korg nutube and ACA monoblock had broken inside the barrel. Thought i'd stuffed the Korg nutube for a minute. Unitil I remembered it had happened once before.
Maybe a slight difference in valve capacitance meant that the other valves tuned to a different station? Parasitic oscillation? Alternatively, maybe you were hearing some residual AM on the carrier.kodabmx said:
Any number of things really, but my construction technique has vastly improved from those days. I didn't even use shielded wire from the RCA to the grid... (Neither did my commercial "Belcor" receiver though).
Speaking of shielded wire... You only connect the shield/ground at one end, yes? I connect it only at the RCA end of the link.
You need a signal and a return to complete a circuit. One way to do that is to connect the RCA outer conductor to chassis, and connect signal ground of PC board to chassis at some point, and that completes the circuit. It also makes a big loop and the shield (connected at only one end) does next to nothing because return current does not pass through the shield. Alternatively, isolate* the RCA from the chassis and run a shielded cable with shield connected at both ends, which completes the circuit, reduces loop area, and makes the shield much more effective.
*but with a small cap from RCA outer connector to chassis to make a shorter path to ground for very high frequency noise.
Indeed!
Whoever said that the occasional bend in the inductor was knot important?
https://pdfs.semanticscholar.org/0048/db56c617d4852c4c4f61f5f09469d66feb3c.pdf
