John Curl's Blowtorch preamplifier part II

[Max Headroom]

Hi Richard, that Extech ground tester looks like a very useful device....any ideas of how it works ?....possible diy ?.


Dan.

 

[Triodethom]

Hi Richard, that Extech ground tester looks like a very useful device....any ideas of how it works ?....possible diy ?.


Dan.

The extech 382357 replacement for the 56 is only 1359 USD . I like your idea Max !

 

[john curl]

Great pictures Richard.

 

[keantoken]

If you put a compliant conductive layer between the resistive sheet and the electrodes and the resistive sheet is essentially incompressible (i.e., hard plastic, not rubber), you can minimize the resistance change with pressure. Otherwise you'll have a surface area effect and a volumetric effect.

To calculate resistance, you need the resistivity in ohm-cm. Multiply by thickness, divide by area.

Thanks a bunch. It seems that the Velostat will work for my needs and I can stack layers, increase area, or squeeze it really tight to get just what I need. In this case, the variable resistance is a good thing, as well as any capacitance of the film.

 

[31697B]

Great pictures Richard.

thanks....... and what about what I said?

-RM

 

[31697B]

Hi Richard, that Extech ground tester looks like a very useful device....any ideas of how it works ?....possible diy ?.


Dan.

No. No idea at all. Its magic.

-RM

 

[Esperado]

No. No idea at all. Its magic.

Look like a clamp Meter.
Fluke Clamp Meters, Amp Meters and Clamp On Ammeters

Just it measure by comparing the currents from a single source to earth through 3 different serial resistances.
You can do the same with a single multimeter.

 

[simon7000]

It works by inducing power into the ground system and measuring the current flow. It assumes that there is more than one path to ground to complete the loop.

For many ground tests the method was to connect a 40 amp fuse between the 120 volt AC power line and the safety ground. If the fuse blew the ground connection was adequate. Really!!!

Of course if you gave a bare ground wire you can measure the voltage across it and the current through it.

 

[Max Headroom]

No. No idea at all. Its magic.

-RM

I now know , that the magic is called stakeless earth testing.
The clamp on head has two coils...one induces current into an earth conductor, and the second coil measures the induced current, the smarts works out the effective loop resistance of the circuit under test.
Might be useful for identifying ''Pin 1"' problems.
Megger DET14C - APPLICATION NOTE is a good primer.

Dan.

 

[john curl]

That too, Richard.

 

[simon7000]

This is my latest project a 1940's style black and white television. It only gets old TV shows.

ES

 

[rayma]

This is my latest project a 1940's style black and white television. It only gets old TV shows.

ES

Those are the best kind.

 

[Nelson Pass]

Harlan Ellison wrote an interesting story about such a TV in the possession of
a child. Of course it wasn't the TV that was doing the trick...

I started to say nice story but I wouldn't want to give the wrong impression
about Ellison's approach to stories.



Correction: Google had it http://en.wikipedia.org/wiki/Jeffty_Is_Five
and it was a radio.

 

[Kindhornman]

Seems like just the right type of TV to watch old shows like Perry Mason and other black and white vintage shows. Gives that vintage feel to an old show that was never in color.

 

[1audio]

This is my latest project a 1940's style black and white television. It only gets old TV shows.

ES

But the tube is supposed to be round with a rectangular mask! The rectangular tubes are from the later 50's.

 

[simon7000]

But the tube is supposed to be round with a rectangular mask! The rectangular tubes are from the later 50's.

Do you know how hard it was to get a working BW tube to begin with!

It is loaded with 500 hours of shows replayed in random order. Goes through the entire list before repeating. I still need to mount the rabbit ears.

 

[scott wurcer]

Do you know how hard it was to get a working BW tube to begin with!

It is loaded with 500 hours of shows replayed in random order. Goes through the entire list before repeating. I still need to mount the rabbit ears.

Defiately looks 50's, I've been cathching up on Boris Karloff's "Thriller" lately. The oldest Perry Mason's are quite a surprise too.

 

[simon7000]

My oldest is Captain Midnight. Newest is the first season of Man from UNCLE. I also got some Captain Gallant and Sgt Preston. The most time was ripping the files. Most were 30 minutes which take 15 to rip! Disc is 1T.

 

[rayma]

Do you know how hard it was to get a working BW tube to begin with!

It is loaded with 500 hours of shows replayed in random order. Goes through the entire list before repeating. I still need to mount the rabbit ears.

Yes, but does it have the commercials too? Those are part of the experience.

 

[simon7000]

Yes, but does it have the commercials too? Those are part of the experience.

Of course. Ovaltine, Black Label Beer, Wildroot Hair Creme etc.