The AM Forum

Hi gang !

I am in the midst of setting up my Clegg Interceptor/Zeus combo for 50.400 AM....

I have a meter issue. The meter in the Zeus is not original. I have to replace it because it was trashed(missing pivot pin) somehow. I have a meter that appears to be the original meter. I have noticed in the Zeus images online that there appears to be a couple of generations of meter types that existed in the Zeus. I have the following meter (see attached).

Does anyone know the design history of the Zeus ? Was the metering circuit changed with the different types of meters ???

One additional point...The schematic I have indicates the meter is 0-3ma full scale. I setup a test circuit(3ma) to see if the movement works. This meter I have that looks like an original appears to be a higher range in terms of current as the indication of 3 ma was very low on the scale when tested. It sure seems like the original meter as far as the scales on the meter face and the mounting holes and size. It fits perfectly. Any thoughts would be appreciated.

The meter I have measures 2-11/16 x 2-7/16 and has four 4-40 mounting studs on it. I see someone wrote 5.4a on the back of it. The other number stamped on the meter is 050363.  ???

I inspected the meter under a magnifier and see nothing obviously wrong with it inside. Movement moves freely so its not getting hang up.

Stephanie

It is possible that Clegg originally used meters that were designed to produce full scale at 3mA... and then switched to meters with different internal shunt resistors.

How much does your meter read when you put 10mA through it? Also, what is the resistance... across the meter... that you measure with a multimeter?

You may be able to use this meter in your transmitter by changing the values of some of the existing meter shunt resistors.

Can you post (or provide a URL for) the schematic of your transmitter?

Stu

Hi Stu ! Nice to hear from you  :)

Well, the meter roughly indicates about 2.25ma with 10 ma.

Meter resistance measures 17 ohms

I have attached the metering circuit portion of the transmitter.

PIN 8 Plate supply is 875 v

Stephanie

Based on your measurements, this particular meter will read full scale (10mA / 400mA) with approximately 45mA flowing through it, and .075V across it.

1. In the "PA plate current" position of the switch:

The actual plate current is flowing through a 10 ohm resistor (as best as I can read the somewhat fuzzy copy of the schematic). If there was (hypothetically) 400mA of plate current flowing, then there would be 4V across the 10 ohm resistor. The original (3mA for full scale) meter would require a total series resistance (including the internal resistance of the meter) of 4V/.003A = 1333 ohms... which is reasonably consistent with the parallel pair of resistors shown in series with the meter in the schematic.

To adjust for the fact that this meter requires 45mA to read fill scale, the total series resistance required (in the plate position of the meter) would be 4V/.045A = 89 ohms. Since the meter has an internal resistance of 17 ohms, you need to use a (89 ohms - 17 ohms) = 72 ohms series resistor in place of the pair of resistors labeled R27 (as best I can read) in the schematic.

Doing so will cause this meter to read full scale (labeled 400mA) when there is 400mA of plate current flowing.

2. In the "PA grid current" position of the meter switch:

You have 39 ohms (as best I can read) in series with the meter... for a total of 39 ohms + 17 ohms = 56 ohms. To make the meter read full scale... indicating 10mA... you need a current of 45mA flowing through it.

But, there is no way to obtain 45mA from the grid leak/self-biasing resistive chain... when there is actually 10mA of grid current flowing up that chain.

Therefore, I don't think that you can use this meter (as is) to correctly read the PA grid current, unless you open up the meter housing and make changes to the meter shunt resistors that are inside the meter housing.

If you want the meter to read 1/5 of the actual PA grid current... you can do that as follows.

a. Remove the 39 ohm series resistor (that is in series with the meter when measuring the PA grid current). I.e. bypass that resistor

b. Change the 15 ohm (as best I can read) resistor at the bottom of the grid leak resistor chain (i.e. one end of that resistor is connected to ground) to a 153 ohm resistor (or 150 ohms will work fine). As a result, when (hypothetically) 10mA of PA grid current is flowing, approximately 9mA (i.e. 90%) of that current will flow through the meter. 9mA flowing through the meter will produce a reading of 20% of full scale (i.e. the meter reading will be 2mA, when the actual PA grid current is 10mA).

Stu

Cool Stu. Thanks for your analysis on this !

Well, Its rather odd that I bought this Clegg gear and was not told anything about the meter snafu. I had the identical looking meter in my junkbox. I dont remember getting that meter with the gear but I suppose I could have just squirreled it away one day not thinking.

I dont see a shunt on this meter. The phenolic board that is attached to the meter terminals inside the meter housing looks quite plain to me. Is the shunt embedded in this phenolic board ?

In any event, I have options here. The other meter was hopeless. Just total junk and not usable. Sigh.

I will continue to probe my resources. I contacted a ham that once worked for Squire Sanders/Clegg and I was hoping to hear back from him. Who knows what may be stored away on someone's shelf somewhere.

I cant tell who manufactured the meter. Ill keep poking the surplus searches and ebay.

Stephanie

 

Stephanie

Just to clarify (because of the low resolution of the schematic you posted)

What is the value of the bottom resistor in the grid leak/self-biasing chain of the PA output tube? This is the resistor that has one side connected to ground. It looks to me to be 15 ohms... but maybe it is something higher in value... like 18 ohms.

What is the value of the resistor that leads from the meter switch to the top (non-grounded side) of the resistor I asked about, above? It looks to me to be 39 ohms... but maybe it is a lower value.

Separately

I am puzzled by the need for 45mA to produce a full scale reading [i.e. (10 / 2.25) x 10mA = 45mA]. Normally, meters like this has a 1mA movement or a 100uA movement. Even if the basic movement requires 3mA for a full scale deflection, it seems to me that there must be a shunt across the meter to divert all but 42mA (out of 45mA) around the basic movement.

If you don't see one, then are you sure that you injected 3mA... and then 10mA... into the meter when you made your measurements? I.e. did you use something like a 1.5V battery in series with 470 ohms... or 12V in series with 3900 ohms to obtain a current source with a sufficiently high impedance to drive a meter with 17 ohms of meter movement resistance?

Stu

Here's the complete schematic.
Don't switch the meter positions with the plate switch on. You will tank the meter forever. One of my Zeus meters says 03 11 63; the other says 166. They both look the same as yours. I believe the Zeus was dropped from the line before Squires Sanders came on board. It's probably not unusual that components might differ from picture to picture and from what was printed on the schematic. Ed's diddling workbench was adjacent to the row of benches where the assemblers were assembling the Zeus, Interceptor, and Clegg 99'er and he would make "on the fly" component changes for one rig, or a numbers of rigs, for any number of reasons. This was late 50's/early 60's; many of the owners, designers, managers were very hands on right at the assembly line.

Correct, those are the values on the schematic.

I used a 9 volt battery and a 3k resistance to test the meter, then a 900 ohm resistance for 10 ma.

It is possible that this meter is not the original meter but a meter from another piece of equipment with the scale face swapped onto it. It looks like a commonly used meter in vintage gear from that period. I just wish I had more of them in my junk box. I went through the Simpson meter page and found that a Model 1227 analog 0-3ma meter would probably fit into that housing nicely and the scale face may even be removable and swapped with the one I have.

ok, good advice. I was following the manual directions for initial tuneup until I heard arcing. The standby/transmit switch was the culprit. It even measured poorly on my ohmmeter. I thought I had done something wrong at first. You missed witnessing the quickest toggle switch reflex action ever pulled off by a ham ;)

I know the sound. I have a third Zeus meter that the original owner wasn't fast enough. The meter pin is permanently now to the right side. The meter spring looks like my hair when I get up in the morning. I did not see any shunts inside the meter housing.

Forgot to ask, did you start on the Interceptor receiver yet?

Pete

Thanks!

Looking at the schematic, and the 0-3 mA meter shown on the schematic:

R26 (15 ohms) and R44 (39 0hms)

When the meter switch is set to read the PA grid current... and if (hypothetically) the PA grid current is 10mA... then 3mA (30%) must flow through the meter to produce a reading of 10mA... and the remaining 7mA (70%) must flow through R26

This implies that the total resistance of the meter + R26, in series, must equal:

15 ohms (R26) x 7/3 = 35 ohms.

[I.e. with 15 ohms in parallel with 35 ohms... 30% of the current will flow through the 35 ohm resistor and 70% of the current will flow through the 15 ohm resistor]

But R26, by itself, is shown in the schematic as 39 ohms.

Therefore, the meter resistance must be very low... and, even then, one would not get an accurate reading of the PA grid current. A full scale meter reading would correspond to somewhat more than 10.8mA of PA grid current.



In the case of the meter switch setting that corresponds to the V4 grid current:

Essentially all of that current will pass through the meter (because R20 has a value of 1kohm).

Therefore, a full scale meter reading, when the meter switch is in this position corresponds to a V4 grid current of 3mA.

With respect to destroying the meter by changing the setting of the meter switch when the HV plate supply is connected to the plate of the PA output tube... via the plate choke:

E.F. Johnson tried to fix this problem by adding a capacitor to ground from each meter terminal. Assuming the two capacitors had roughly equal values... this would reduce sudden, large changes in the voltage across the meter when moving the meter switch between the PA plate current position, and one of the other positions (or vice-versa). This solution does result, however, in sparking across the contacts of the meter switch. There are other solutions that work better. In my Ranger, I have removed the two capacitors (one from each side of the meter to ground)... and placed a single capacitor across the meter terminals. Therefore, the capacitor always has very little voltage across it... but the voltage across the meter cannot jump suddenly. Another solution is to use a pair of anti-parallel diodes to clamp the voltage across the meter (in either direction) to around 0.7V.

Stu

Yes, it works fine !  I was listening to it last Sunday. It didnt like the VHF contesters on the mountains to the north of me  :(

But it works fine otherwise.

Understood Stu. I wonder if this other meter I have was cooked previously and why it seems to misindicate. The meter movement seems ok and the springs looks somewhat deformed from what I remember that they are normally coiled on the same plane so to speak.

Pete, I wonder if you might be able to confirm your meter performance if you have lots of free time this afternoon ;) Just thought Id ask anyway.

Pete
Stephanie

It would also be interesting to know what the resistance of the meter in Pete's xmtr is when the meter switch is in the off position.

If it is 17 ohms ... then I suspect that the Clegg engineers made an error in calculating how big the sum of the meter resistance and R44 had to be.

They probably (incorrectly) calculated that this sum has to be 10/3 x 15 ohms = 50 ohms... which would lead to a value of R44 of 33 ohms (which still doesn't explain why the value in the schematic is 39 ohms)

But, this sum has to be 7/3 x 15 ohms = 35 ohms... and the correct value for R44 would be 18 ohms.

Stu

Stephanie,
The meter in your first entry looks just like the one in my Zeus.
I don't have it running but can take some measurements and pictures if you would like.

That would be awesome if you could measure the meter resistance with the switch in the off position. Perhaps a test with a 9volt battery and a 2.7k resistor would produce a full scale reading if the meter is in fact a 3ma full scale as we believe. A picture or two would be icing on the cake :)

17 ohms is about right for a 3ma meter movement.  Most 1ma meter movements measure about 50-60 ohms.  Your meter is most likely a 1ma movement with a internal shunt making it read 3ma full scale.

Fred

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.

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

IMPORTANT INFO TO NOTE:

I pulled out an older Zeus manual. This is an early version where all sheets were done by mimeograph (blue fuzzy, fading print). I reviewed and compared the parts lists for the later version and the older version in the resistor section.

On the newer prints: R25 is 5.8K, R26 150 ohms
Older print: R25 is 6.8K, R26 15 ohms
On both part lists, R27A is stated as "selected and added as required"

The schematic is labeled CL-10-257C. It is the only schematic I could ever find on the Zeus. The schematic shows the values for the older version. Most likely, somewhere along the production time line, meter was changed (had a different internal resistance), causing them to change the resistor values, updated the parts list, but never changed the schematic. So assuming you're getting strange meter readings but the transmitter appears to be working properly, and given the meter you have installed, I would check the resistor values above you have presently installed in the rig.

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

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 :)

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

I agree with Stu, drafting errors

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

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.

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


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.

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.

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 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

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

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

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

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

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

Charlie, WA3UTC