10-22-2017, 09:00 PM
I stand corrected. I was reading milliamps as amps because of where the meter put the decimal, and with another meter I confirmed I was off by a factor of 100. Today I got about .7 mA. Still enough to tickle, and still enough to make little tiny sparks if you drag the ground wire across the chassis.
As for the statement of how much current can kill, I will remind you my measurement was to ground, not through my body. I think my body draws only a few microamps, so even touching a full 15 Amp service, I'm still OK. (I wouldn't have made it out of Jr. High Electronics if that wasn't true!)
I've been shocked off the antenna lead before, on an unrestored radio because it had a bad ground connection and I assumed the line bypass caps were leaky. But now I think the tickle was normal if the chassis isn't grounded.
And just to be sure I'm seeing what I think I'm seeing, I assembled a couple of .01 caps in a Y configuration across the line and measured about 60 Volts to ground, and about .4 mA between the apex and ground. It was still enough to feel. The current going through my body wasn't enough to register because, as I've been told by my boss, I have high resistance! ;-)
So, I guess I've answered my own question about it being normal to feel a potential between the chassis and ground, and reducing the bypass caps to .01 doesn't help much, so the only thing left is to get opinions from others who have seen the issue with hum, and what solutions you've come up with for hum and noise. (Besides making a loop, which I understand would reduce static to some degree due to some "magic" I don't understand about propagation.) Right now, a .0022 uF cap between the chassis and ground seems the best compromise, providing a decent path for RF to ground with a high impedance at 60 Hz.
For my own use, I'm not as concerned about a few microamps of current as I am about the fact that if I connect the ground as designed, I get more hum and noise.
I guess for now, nothing to do but put 'er back in the case and use my longer wire antenna and see where that gets me.
Dan
As for the statement of how much current can kill, I will remind you my measurement was to ground, not through my body. I think my body draws only a few microamps, so even touching a full 15 Amp service, I'm still OK. (I wouldn't have made it out of Jr. High Electronics if that wasn't true!)
I've been shocked off the antenna lead before, on an unrestored radio because it had a bad ground connection and I assumed the line bypass caps were leaky. But now I think the tickle was normal if the chassis isn't grounded.
And just to be sure I'm seeing what I think I'm seeing, I assembled a couple of .01 caps in a Y configuration across the line and measured about 60 Volts to ground, and about .4 mA between the apex and ground. It was still enough to feel. The current going through my body wasn't enough to register because, as I've been told by my boss, I have high resistance! ;-)
So, I guess I've answered my own question about it being normal to feel a potential between the chassis and ground, and reducing the bypass caps to .01 doesn't help much, so the only thing left is to get opinions from others who have seen the issue with hum, and what solutions you've come up with for hum and noise. (Besides making a loop, which I understand would reduce static to some degree due to some "magic" I don't understand about propagation.) Right now, a .0022 uF cap between the chassis and ground seems the best compromise, providing a decent path for RF to ground with a high impedance at 60 Hz.
For my own use, I'm not as concerned about a few microamps of current as I am about the fact that if I connect the ground as designed, I get more hum and noise.
I guess for now, nothing to do but put 'er back in the case and use my longer wire antenna and see where that gets me.
Dan
"Why, the tubes alone are worth more than that!" (Heard at every swap meet. Gets me every time!)
Philcos: 90, 70, 71B, 610, 37-61 40-81, 46-420 Code 121 to name a few.
Plus enough Zeniths, Atwater Kents and others to trip over!
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