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Author Topic: Clegg Zeus Transmitter meter  (Read 22101 times)
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KA2DZT
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« Reply #25 on: September 21, 2015, 10:19:45 PM »

Changing R25 from 6.8k ohms to 5.8k ohms will have essentially no useful purpose, because it will simply reduce the negative bias on the clamp tube (by around 20%) when normal grid current is flowing. Since 5.8k ohms was not a standard value (in that era), this is probably a drafting error.

Changing R26 from 15 ohms to 150 ohms will cause 75% of the PA grid current to flow through the meter. That doesn't seem to make sense with a 3mA FS meter whose face reads 10mA. This too is probably a drafting error.

Stu

I agree with Stu, drafting errors
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KA2DZT
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« Reply #26 on: September 22, 2015, 01:05:43 AM »

Ill probably be at a party sometime this week but I knew the meter was made by Ideal Precision already. Its say so in the Zeus manual parts list Smiley

Your meter is also 17 ohms eh ? What does it indicate with 3 ma flowing through it ? Inquiring minds want to know ! Smiley

I'm not sure it was mentioned, but the meter was made by Ideal Precision. Good to know if it's brought up at your next cocktail party. Also, the resistance of one of my meters is 17.4 ohms.

Stephanie,

Your current measurements are not making any sense.  A meter that is 10ma full scale should not be reading only a few ma with 10 ma current.  I suspect there may have been some error in the manner you conducted the test.  You need to have a separate current meter in series with the meter under test.  Use a battery and series resistor in series with the two meters.  Reduce the series resistor to produce a full scale reading. Read what current (shown on the separate milliamp meter) it requires to produce the full scale reading. It should take 3ma to produce full scale.

If you get the same results as before, the meter may have been modified for some reason or is damaged.  Although, that style meter is not easy to open without breaking the plastic housing.

Fred
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KA2DZT
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« Reply #27 on: September 22, 2015, 11:53:03 AM »

Stephanie,

Looking at the schematic that Pete posted, I see another problem with the grid current meter circuit.  R-44 is the wrong value.  R-44 is in series with the meter and both are in parallel with the 15ohm resistor to ground.  The meter is suppose to be 3ma full scale with a 10ma max scale reading.  If this is true, we would know that 7ma must flow through the 15ohm resistor leaving 3ma to flow through R-44 and the meter to read a total of 10ma.  7ma X 15ohms = .105V,  .105V/3ma = 35ohms.  The total resistance of R-44 and the DC resistance of the meter should be 35ohms.  We know the meter resistance is 17ohms.  If this is true, R-44 should only be 18ohms and not 39ohms.

Poor engineering, the designer did the calculations,  came up with 35ohms, picked the standard value of 39ohms as close enough, completely overlooking the DC resistance of the meter.  You could almost do this when calculating the plate current meter circuit but not with the grid current meter circuit.

The plate current meter circuit can be calculated in the same manner.  You'll notice that R-27 and R-27A have to be adjusted to have the plate current read correctly.

Fred.
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Pete, WA2CWA
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« Reply #28 on: September 22, 2015, 03:47:02 PM »

In an earlier post, John's meter resistance was measured at 37.9 ohms

hi Stephanie,
My meter measures 37.9 ohm's.
My Pictures aren't much and I am trying to reduce them in size.
John

I haven't had a chance to measure my other meter. I also haven't had the time to look under the chassis and trace out what resistors are actually in there.
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« Reply #29 on: September 26, 2015, 04:18:56 PM »

Hi Fred,

The original meter is supposed to be a 3ma full scale. With 3 mils applied it indicates WAY too low...Its hosed but I will keep looking for an original replacement. In the interim, I have found a nice 1ma Simpson that fits nicely. I am going to adapt this meter for the Zeus. The meter has a 40 ohm internal resistance and I confirmed it reads 1ma full scale with the correct current.

Ill probably be at a party sometime this week but I knew the meter was made by Ideal Precision already. Its say so in the Zeus manual parts list Smiley

Your meter is also 17 ohms eh ? What does it indicate with 3 ma flowing through it ? Inquiring minds want to know ! Smiley

I'm not sure it was mentioned, but the meter was made by Ideal Precision. Good to know if it's brought up at your next cocktail party. Also, the resistance of one of my meters is 17.4 ohms.

Stephanie,

Your current measurements are not making any sense.  A meter that is 10ma full scale should not be reading only a few ma with 10 ma current.  I suspect there may have been some error in the manner you conducted the test.  You need to have a separate current meter in series with the meter under test.  Use a battery and series resistor in series with the two meters.  Reduce the series resistor to produce a full scale reading. Read what current (shown on the separate milliamp meter) it requires to produce the full scale reading. It should take 3ma to produce full scale.

If you get the same results as before, the meter may have been modified for some reason or is damaged.  Although, that style meter is not easy to open without breaking the plastic housing.

Fred
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Stephanie WX3K
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« Reply #30 on: October 02, 2016, 03:40:28 PM »

Ok, its a rainy weekend and I made time to take a look at the Clegg again. Over the time since, I have found an physically exact replacement meter. An Ideal precision meter that allows me to use the original meter face but it has a 50 ua movement. Internal meter resistance seems to be 2k. I have also been poking through the Clegg to verify resistor values.

In the PA grid circuit, R25 is a 2 watt 6.8k. R26 are two 30 ohm 1/2 watters in parallel. R44 is a 1% 40 ohm.

In the PA plate circuit, R28 is a 2 watt 10 ohm guy. R27 a 1500 half watter is in series with a 220 phm metal film jobber, an obvious mod.

So, I need to develop a new shunt for my 50ua meter to correctly meter the grid and plate circuits.

So do I modify the shunt so the new meter acts like a 3ma FS meter and go with the original values in the circuit ? I would have to remove the 220 metal film jobber to return the Clegg to original.

Suggestions ?




Hi Fred,

The original meter is supposed to be a 3ma full scale. With 3 mils applied it indicates WAY too low...Its hosed but I will keep looking for an original replacement. In the interim, I have found a nice 1ma Simpson that fits nicely. I am going to adapt this meter for the Zeus. The meter has a 40 ohm internal resistance and I confirmed it reads 1ma full scale with the correct current.

Ill probably be at a party sometime this week but I knew the meter was made by Ideal Precision already. Its say so in the Zeus manual parts list Smiley

Your meter is also 17 ohms eh ? What does it indicate with 3 ma flowing through it ? Inquiring minds want to know ! Smiley

I'm not sure it was mentioned, but the meter was made by Ideal Precision. Good to know if it's brought up at your next cocktail party. Also, the resistance of one of my meters is 17.4 ohms.

Stephanie,

Your current measurements are not making any sense.  A meter that is 10ma full scale should not be reading only a few ma with 10 ma current.  I suspect there may have been some error in the manner you conducted the test.  You need to have a separate current meter in series with the meter under test.  Use a battery and series resistor in series with the two meters.  Reduce the series resistor to produce a full scale reading. Read what current (shown on the separate milliamp meter) it requires to produce the full scale reading. It should take 3ma to produce full scale.

If you get the same results as before, the meter may have been modified for some reason or is damaged.  Although, that style meter is not easy to open without breaking the plastic housing.

Fred
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Stephanie WX3K
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« Reply #31 on: October 02, 2016, 05:59:52 PM »

hi Stephanie .... I would say that going back to original values in the rig and one simple shunt across th meter terminals would be easiest .... the shunt resistor value will wind up being quite low and may have to be custom made .... I usually did this with solenoidal coiled tinned buss wire and could selectively short out turns with solder bridges or wire to calibrate it .... a current limited power supply or any lv dc supply and a current limiting resistor should do the trick
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KA2DZT
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« Reply #32 on: October 02, 2016, 10:28:23 PM »

Fairly difficult to get a shunt accurate enough to make the 50ua meter read correctly.  I did a few quick calculations and based on the 2K ohms of the 50ua movement the shunt resistance is around 33 ohms.  Better to use a shunt higher in resistance (say 50 ohms) and use a resistance in series with the meter to calibrate the 50ua meter to read full scale when 3 ma is past through the shunt.

It's also tricky to measure the resistance of the 50ua movement without pinning the needle.  Use a series resistor with the meter and measure the meter with the series resistor.  Most ohmmeters have at least a few volts at the leads so start with 40-60K as the series resistor.  Digital ohmmeters may vary as to what voltage is at the leads.  So, the series resistor needs to be 20Kohms/V

Fred
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« Reply #33 on: October 03, 2016, 11:27:13 AM »

I agree with Fred .... shoulda computed Ohms law first
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Beefus

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« Reply #34 on: October 13, 2016, 09:38:27 PM »

Yep Fred, 50ua is pretty sensitive. I will have to tinker a bit.

Fairly difficult to get a shunt accurate enough to make the 50ua meter read correctly.  I did a few quick calculations and based on the 2K ohms of the 50ua movement the shunt resistance is around 33 ohms.  Better to use a shunt higher in resistance (say 50 ohms) and use a resistance in series with the meter to calibrate the 50ua meter to read full scale when 3 ma is past through the shunt.

It's also tricky to measure the resistance of the 50ua movement without pinning the needle.  Use a series resistor with the meter and measure the meter with the series resistor.  Most ohmmeters have at least a few volts at the leads so start with 40-60K as the series resistor.  Digital ohmmeters may vary as to what voltage is at the leads.  So, the series resistor needs to be 20Kohms/V

Fred
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Stephanie WX3K
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« Reply #35 on: October 13, 2016, 09:56:12 PM »

I used my Fluke 77 and ranged through the ranges until i got the meter to produce the most upward movement without pinning it.

<snip>

It's also tricky to measure the resistance of the 50ua movement without pinning the needle.  Use a series resistor with the meter and measure the meter with the series resistor.  Most ohmmeters have at least a few volts at the leads so start with 40-60K as the series resistor.  Digital ohmmeters may vary as to what voltage is at the leads.  So, the series resistor needs to be 20Kohms/V

Fred
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Stephanie WX3K
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« Reply #36 on: February 11, 2020, 10:14:51 PM »

Stephanie, were you able to sort out your meter issue, if so what were your results?

Charlie, WA3UTC
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