Dennis

Why do I get this error in some of the feeds on topics?

“This message has not been downloaded from the server”.

I will see several Post but randomly thru the conversation posts don’t show up.

Craig

Graham,

Yeah, those readings made no sense to me, and when the AC was consistently between 2.2 and 2.3 times the DC, I figured something wasn't kosher.

I've got an old Radio Shack Micronta 22-291U, It says 20,000Ω/V DC and 10,000Ω/V AC. Not sure if that helps. I think it's at least 30 years old. Nothing in the manual about a blocking capacitor.

Open to suggestions for a better DMM. I'd like a good compromise between top-of-the-heap and price, but not leaning too heavily on price if the compromise is going to have me disappointed and needing yet a better one down the road. I get the impression that the Flukes tend to be more idiot proof, but there sure is a premium to be paid for that. I'd be open to a bench meter if that saved me some money, because I can do pretty well with what I've got when it comes to portability. You know, troubleshooting vehicle electrical problems and such.

Bruce

On May 23, 2020, at 12:07, "sdturne@q.com" <sdturne@q.com> wrote:

For instruments like the 114 pulse generator, 184 time mark generator, and more. Does anyone know of a good place to either get these power cables? I have one, that came with my Type 114. With a 184 on the way, I'd like to find another.

Thanks!

Sean

I have used your offline composition method before. I just got lazy. Have been composing offline for any lengthy posts since losing that one.

Yes! I like plumbing analogies, as I have (too much) experience with plumbing, having almost replaced the entire plumbing system in my house this spring, both fresh water and drains. I moved to a 1970 house from a 1954 house, and had far less trouble with the 1954 plumbing in 18 years than the 1970 plumbing in two.

I'm still making my way through the manual and the electronics book. Maybe I should do more of that and less time on the forum, but this is more fun.

Your comments on component substitutions are just what I needed! Very helpful, thank you!

And thanks, also, for the additional sources for components. Ebay has selections of 500 caps of various values for under $15, but I don't know if I'd use most of them. For now, I'll order what I need with at least a few to spare, keeping in mind the higher quantity price advantage. And I'll familiarize myself with the older devices I have around here and decide which to attempt to fix and which to cannibalize. I assume most components will still be good, and I can test them more reliably as I pull them, but I'm less confident of older caps. I do have an ESR tester, though, so should be able to tell how bad they might be in spite of having capacitance within spec.

I am going to watch for surplus from local universities and colleges. I'm also still trying to find local Facebook groups that might become a similar resource.

Thanks again! I'll be referring back to your post!

Bruce

First, please respond directly to me only OFF-list, and only with
relevant info. I don't want to get off on another huge Deoxit
good/bad/whatever discussion, which has been covered many times. I
would just like any feedback or experience info on whether Deoxit would
help to improve mechanical switch contact performance used in very low
level circuits.

One of my projects involves boxing up some special transformers and a
switching system, for isolating and dividing down AC signals by large
factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number
of switching elements are needed to route and select various
transformer output taps to send to the single output connection. There
are two transformers to cover two frequency bands
10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the
decade dividing. The switching elements need to have as low an on
resistance (<< 1 ohm) as possible, and function well at extremely low
levels. Since this is an AC system, I'm not worried about Seebeck
effects, just the low level contacting ability. The primary sides of
the transformers are at more normal levels, so the switches there are
not critical.


I have all sorts of nice low level regular and Hg reed relays that
would do the job, but since the output side is to be isolated, to
minimize interference, it would be much better to do all the switching
passively with mechanical switches. This would avoid needing
electricity, and the proximity problems of having relay coils and
capacitance in the low level environment, and power supply and line
noise and ground loops (no power cord), or messing with battery power.
Especially, there would be no power transformer emissions to worry
about.

I have lots of mechanical switches of all sorts. I'd like to go with a
rotary wafer type to select the transformer taps and frequency ranges.
I have mostly standard Ag plated type contact ones and some Au ones. I
can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds
actuated by a mechanically driven magnet, but doing that would be a big
project in itself, so scratch that, unless a simple way pops up.
Another way is to make heavy analog switches with big MOSFETs, but
that's a lot of parts, a battery, and issues with capacitance and
crosstalk. So, good old mechanical switching seems the best way to go -
if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed
contact to be usable in the nV region. Wetting the contacts with Deoxit
is the only practical thing I can picture so far. There is another
class of contact "protectors" based on synthetic oils, but I think I
need chemical action too, so these may not work - I'll have to
investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would
behave for low level contacts? It may boil down to a "try it and see"
scenario, but it would be nice to have some info in
advance. OFF-list only, please.

Ed

Albert,

R1478 which should be 3.6 ohms measures 3.2 on analog, 3.6 on digital.

R1468 which should be 0.6 ohms measures 0.7 on analog, 0.7 on digital.

So not far off. I do trust my analog more because it doesn't bounce around like the digital. In fact, I measured again just now with the digital, and could not get a reading above zero on either resistor, while the analog repeated the earlier readings. Pfft! I probably need a better DMM, but used Fluke 87 III's are about $100. Any suggestions?

Thanks,

Bruce

On May 23, 2020, at 6:15 PM, ciclista41 via groups.io <ciclista41=yahoo.com@groups.io> wrote:

Hi again, Dave.

Here are the readings I just took across the test points:

DCV, then ACV

110 = 87 225

50 = 37.5 90

15 = 12 22.5

5 = 3.5 4.2

-15 = -14.2 32.5

-8 = -5.7 18.5

UNREG 50 = 40 102.5

105 = 7.5 20.5

Either I am measuring incorrectly or something is WAY off from expected, but from these readings, I'm not seeing evidence of which rectifier to focus on. Also, I thought AC measurements were supposed to be taken in series with the thing being tested, not parallel to them.

Bruce

The pin out of the pass transistors changed when that happened. At one point Tek realized this would probably happen again and they modified their PC Boards with extra pads on the board so wire jumpers could be installed to adjust for >any orientation of the pins during manufacturing.<<

First, please respond directly to me only OFF-list, and only with relevant info. I don't want to get off on another huge Deoxit good/bad/whatever discussion, which has been covered many times. I would just like any feedback or experience info on whether Deoxit would help to improve mechanical switch contact performance used in very low level circuits.

One of my projects involves boxing up some special transformers and a switching system, for isolating and dividing down AC signals by large factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number of switching elements are needed to route and select various transformer output taps to send to the single output connection. There are two transformers to cover two frequency bands 10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the decade dividing. The switching elements need to have as low an on resistance (<< 1 ohm) as possible, and function well at extremely low levels. Since this is an AC system, I'm not worried about Seebeck effects, just the low level contacting ability. The primary sides of the transformers are at more normal levels, so the switches there are not critical.


I have all sorts of nice low level regular and Hg reed relays that would do the job, but since the output side is to be isolated, to minimize interference, it would be much better to do all the switching passively with mechanical switches. This would avoid needing electricity, and the proximity problems of having relay coils and capacitance in the low level environment, and power supply and line noise and ground loops (no power cord), or messing with battery power. Especially, there would be no power transformer emissions to worry about.

I have lots of mechanical switches of all sorts. I'd like to go with a rotary wafer type to select the transformer taps and frequency ranges. I have mostly standard Ag plated type contact ones and some Au ones. I can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds actuated by a mechanically driven magnet, but doing that would be a big project in itself, so scratch that, unless a simple way pops up. Another way is to make heavy analog switches with big MOSFETs, but that's a lot of parts, a battery, and issues with capacitance and crosstalk. So, good old mechanical switching seems the best way to go - if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed contact to be usable in the nV region. Wetting the contacts with Deoxit is the only practical thing I can picture so far. There is another class of contact "protectors" based on synthetic oils, but I think I need chemical action too, so these may not work - I'll have to investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would behave for low level contacts? It may boil down to a "try it and see" scenario, but it would be nice to have some info in advance. OFF-list only, please.

Ed

On May 23, 2020, at 12:07, "sdturne@q.com" <sdturne@q.com> wrote:

For instruments like the 114 pulse generator, 184 time mark generator, and more. Does anyone know of a good place to either get these power cables? I have one, that came with my Type 114. With a 184 on the way, I'd like to find another.

Thanks!

Sean