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Old 11th Mar 2020, 10:53 pm   #1
regenfreak
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Default Heathkit Q meter movement won't zero

Hi
I have persistently been looking for a Q meter over a year in the UK with no luck. I have been designing, wounding many antenna and oscillator coils lately because I have been homebrewing many superhets. Also I build a one foot diameter ferrite sleeve loop antenna made out of 75 ferrite sticks. I really need to measure the coils' Q.

I have finally imported a Heathkit QM-1 from abroad at very a high cost. It has all the internal components intact with some minor corrosion. The external calibration test coil is missing which i can work around it.

I won't power it up until i change the electrolytic filter caps for the 6X5 rectifier tube.

The movement of the Q meter (50 micro ampheres type) is offset to the left when it is powered off. I cannot reset the movement mechanically by turning the adjustment screw. Is the movement damaged? Or the zero adjustment catch mechanism came loose from being knocked about?

My only hope is that I can reset it to zero electrically as there is a zero dial on the panel.
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Old 11th Mar 2020, 11:31 pm   #2
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Default Re: Heathkit Q meter movement won't zero

Can you check to see if the hairspring coils have tangled? This can cause zeroing problems.

I think that the clear perspex cover on Heathkit meters will just pop off the meter body if gently squeezed from the sides, allowing closer inspection of the hairsprings and zeroing mechanism.

Ron
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Old 12th Mar 2020, 12:03 am   #3
regenfreak
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Default Re: Heathkit Q meter movement won't zero

Ron
Many thanks for the suggestion. I have tried to squeeze the Perspex cover on vertical or horizontal sides, it won't pop off. I cannot see the hairspring coils clearly. I don't think the hairspring is broken because when I rotate the chassis 90 degrees vertically, the movement rotates to the right for some divisions due to gravity. Oddly enough the screw zero reset works when the chassis is tilted vertically but it does not work in horizontal operating position.


The reset mechanism consist of a black plastic bit rotated by the screw and it is inside an elongated brass slot which drives the movement via a kind of mini brass lever. I will try to pop out the Perspex cover when I gather more Dutch courage. I will try to get a close up photo.
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Old 12th Mar 2020, 12:12 am   #4
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Default Re: Heathkit Q meter movement won't zero

Here are the closest I can get. I have no experience with repairing movement for AVO meter.
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Old 12th Mar 2020, 12:30 am   #5
ronbryan
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Default Re: Heathkit Q meter movement won't zero

Can you see the brass slotted part move when the zeroing screw is operated? Does this have any effect on the pointer position?

You may find that removing the meter by disconnecting the terminals and undoing the fixing screws will help you see how the clear cover is fixed. The meters I have seen have small lugs on the perspex which clip into the meter body, but there may be differences in US made movements.

On a Heathkit instrument I have here with a Pullin meter, you can remove the clear cover with two hands by placing fore fingers on the top of the cover either side and thumbs on the bottom either side of the cover and gently tilting the top of the cover away from the instrument. Then withdraw the bottom of the cover, disengaging the adjuster pin from the slotted brass bit.

Ron

Last edited by ronbryan; 12th Mar 2020 at 12:40 am.
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Old 12th Mar 2020, 12:51 am   #6
regenfreak
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Default Re: Heathkit Q meter movement won't zero

Ron
The brass slot part moves if i turn the screw but it wont engage the movement. If i rotate the chassis 90 degrees vertically, the brass slot part engages with the movement. However it offsets to the left once i rotate the chassis back horizontally.
I may be able to get access to the hairspring but i will need to open it up from the rear perspex cover, meaning desoldering and dissembling the components. To untangle the hair spring is not my cup of tea as i lack the finger dextersity of a watchmaker and the experience.

Perhaps in the worst case scenerio, i will have to buy another Heathkit Q meter with undamaged movement and swap parts.

PS I will try to remove the cover. I dont understand how the adjustment slot works mechanically so i dont trust myself or do anything that may damage it further.

Last edited by regenfreak; 12th Mar 2020 at 1:03 am.
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Old 12th Mar 2020, 1:38 pm   #7
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Default Re: Heathkit Q meter movement won't zero

Quote:
Originally Posted by regenfreak View Post
Ron
The brass slot part moves if i turn the screw but it wont engage the movement. ...
Hi regenfreak,

I do not understand that statement!
If that slot is moving back and forth, that should move that small tab at the top side (it is part of the same piece) to which the hairspring is soldered. If the pointer and the moving coil is free to move then adjusting the screw should move the pointer.

In that adjustment screw there is a pin, eccentric to the center, and it is engaged in the middle of the slot.
As you turn the screw you should see the slot and the top tab moving back and forth.
Sometimes, when assembled incorrectly, the pin is not in the middle of the slot, just next to the slot part, it will just move the slot part and the tab to one side but not back.
In that case you need to remove the cover with the screw, reinsert/reassemble the cover with the pin engaged in the slot.

Bottom line is you need to remove the cover and see what is really going on.
If the slot part is moving as it is supposed to, and you still can not center the pointer, at the bottom there is a similar bearing/hairspring assembly, which can be similarly rotated just like the top part, except there is no slot/pin adjusting assembly.
In that case move the slot part vertical (that is the mid position) and then adjust the bottom part that the pointer is set correctly, then you will have proper range of zero pint adjustment with the screw.

Hope I did not make it sound too confusing, but you will see it once have taken off the cover.

Regards, Peter
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Old 12th Mar 2020, 9:12 pm   #8
regenfreak
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Default Re: Heathkit Q meter movement won't zero

Dear Peter
Thanks for the suggestions. Sorry I had problem with describing the mechanism.

Quote:
In that adjustment screw there is a pin, eccentric to the center, and it is engaged in the middle of the slot.
As you turn the screw you should see the slot and the top tab moving back and forth.
Yes it is in the middle of the slot and the top tab is moving back and forth as I turn the screw. But the movement does not move even the top tab is moving.

I have forcefully squeezing the perspex front cover many times but it wont pop out no matter what.

I am trying to picture your explanation in my head but it is not so easy without removing the cover. The Q meter construction looks a bit like this but it is not exactly the same:

https://www.w8ji.com/Repairing%20heathkit%20meters.htm


I will need to do some research and understand how they are mechanically connected and working together. These pages look relevant:

https://www.petervis.com/avo-meters/...nt-repair.html

https://jacmusic.com/Tube-testers/AV...ube-Tester.htm

Last edited by regenfreak; 12th Mar 2020 at 9:27 pm.
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Old 12th Mar 2020, 11:22 pm   #9
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Default Re: Heathkit Q meter movement won't zero

Hi Peter
I managed to open it with little force by gently squeezing the sides with fingers and slide a mini screwdriver under the Perspex bezel.

I can confirm that the eccentric pin (2nd photo)was correctly centered inside the slot (1st photo)but it does not activate the movement when I turn the screw.

I can only center the movement by turning the slot all the way to the left (see 3rd photo) with the cover removed. It is not supposed in this position. Therefore, there is something wrong there. This is a temporary fix at the moment.

I can see the hairspring, there is no spider web or particle trapped inside. I blew the movement with my mouth and it swung all the way to the right. therefore it is not sticky movement or electrostatic charge on the bezel

Quote:
If the slot part is moving as it is supposed to, and you still can not center the pointer, at the bottom there is a similar bearing/hairspring assembly, which can be similarly rotated just like the top part, except there is no slot/pin adjusting assembly.
In that case move the slot part vertical (that is the mid position) and then adjust the bottom part that the pointer is set correctly, then you will have proper range of zero pint adjustment with the screw.
I don't quite see "a similar bearing/hairspring assembly at the bottom".
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Old 13th Mar 2020, 1:32 pm   #10
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Default Re: Heathkit Q meter movement won't zero

Quote:
Originally Posted by regenfreak View Post
...
I don't quite see "a similar bearing/hairspring assembly at the bottom".
Hi regenfreak,

You need to remove the scale form the meter movement and take out the whole movement from the bottom part of the case. Just be careful, the pointer can be damaged quite easily when nothing is "protecting", surrounding it.
There are bolts at the bottom of the case, screwing into the meter movement, and also two wires connecting the meter movement coil to the terminals on the case.
There is an exact similar bearing assembly at the bottom of the meter movement supporting the coil, with the same hairspring. The two hairsprings are the two leads to the coil.
That assembly that has the bottom hairspring can be rotated, similarly to the top one, though there are no slot parts, e.t.c.
Once you have the meter movement out of the case you will see it.

EDIT:
The picture on the "AVO Mk4 tube tester restoration" web-page, next to the chapter titled "Balancing of the meter" shows a picture of a meter movement out of its case. It also shows the wire attached to the bottom bearing assembly, that orange-white striped wire. Where the wire is soldered to, that piece can be rotated similarly to the top spring assembly with the slot, and you can zero the pointer that way.

Regards, Peter

Last edited by orbanp1; 13th Mar 2020 at 1:45 pm.
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Old 13th Mar 2020, 1:45 pm   #11
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Default Re: Heathkit Q meter movement won't zero

Be vey careful to make sure that there are no metal particles such as filings around the work area. Once these get attracted to the meter's magnets they're very difficult to get out.
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Old 13th Mar 2020, 4:57 pm   #12
regenfreak
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Default Re: Heathkit Q meter movement won't zero

Thanks Peter and Graham

It has become clearer to me now. This is an enlarged picture of the AVO MK4 assembly:

https://jacmusic.com/Tube-testers/AV...ect-2/PIC3.jpg

It will be a delicate operation. I will need to remove the meter from the chassis which itself is not a trivial task. I have a vintage National Physical laboratory 50 microamphere meter and some cheapo chinese milliamphere meters for dry run practice.

One observation: the Heathkit Q meter movement rotates about 30 degrees when it is tiled 90 degrees angle to the horizon, while the movement of the National Physical Laboratory only rotates about 2-3 degrees. it seems that most meters' movement are balanced on the horizontal position taking the effect of gravity into consideration during the calibration.
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Old 13th Mar 2020, 5:20 pm   #13
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Default Re: Heathkit Q meter movement won't zero

There are normally little balance 'weights' (tiny coils of wire) on arms attached to the moving coil. One opposite the pointer (to balance the weight of the pointer) and 2 on arms at right angles to it. I wonder if one has moved or fallen off.

Years ago I was told that most panel-mouting meters were calibrated assuming the scale plate was vertical, while most portable test meters (like AVOmeters) were calibrated assuming the scale is horizontal. While it may be necessary to know this for accurate work, no correctly set up moving coil meter should move by 30 degrees between those 2 positions.
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Old 13th Mar 2020, 6:14 pm   #14
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Default Re: Heathkit Q meter movement won't zero

If a coil is properly balanced, there should be no movement whatever position it is placed.
My GEC Super 50 Selectest, a 20,000 ohms per volt meter like the better AVOs, has normal feel for horizontal use, but it also has the "front end" casing moulded for vertical mounting.
If a meter is only ever used (say) in a fixed vertical panel, balancing may be legitimately ignored in other planes.
Les
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Old 13th Mar 2020, 8:07 pm   #15
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Default Re: Heathkit Q meter movement won't zero

I noticed that your meter has "Benton Harbor, Mich." on the scale at the bottom right and "MVT. MADE IN USA BY WESTON". This says to me that the Q meter was made in the USA and, if it has mains power, that will be the usual US mains. If someone has inadvertently assumed that it works on UK mains, that might well have done some damage to the meter movement. Just an observation.

Colin.
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Old 13th Mar 2020, 11:28 pm   #16
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Default Re: Heathkit Q meter movement won't zero

thanks Tony and Les

Quote:
There are normally little balance 'weights' (tiny coils of wire) on arms attached to the moving coil. One opposite the pointer (to balance the weight of the pointer) and 2 on arms at right angles to it. I wonder if one has moved or fallen off.


While it may be necessary to know this for accurate work, no correctly set up moving coil meter should move by 30 degrees between those 2 positions.
Quote:
If a coil is properly balanced, there should be no movement whatever position it is placed.
This is my worst fear. You are right. I have compared the Q meter with my other meters, all of them rotates very little in vertical position (see photo). Out-of-balance movement may affect the linearity and sensitivity. It is going to be hard to rebalance the movement as the spring has to be removed and a replacement counterweight has to attached the right position.

I can check roughly its linearity ( in term of angle of rotation, ignoring the non-linear Q-scale) by wiring the National Physical Laboratory 50uA microammeter in series with the de-soldered Q meter, use a variable DC power supply, two high impedance digital multimeters, a 1M potentiometer, something like this:

https://www.nutsvolts.com/magazine/a...-analog-meters

In the worst case scenario, I will have to wait for ages and buy another Heathkit Q-meter with a working movement and swap the good parts.

Quote:
I noticed that your meter has "Benton Harbor, Mich." on the scale at the bottom right and "MVT. MADE IN USA BY WESTON". This says to me that the Q meter was made in the USA and, if it has mains power, that will be the usual US mains. If someone has inadvertently assumed that it works on UK mains, that might well have done some damage to the meter movement. Just an observation.
The Q meter measures the resonance voltage for the LC tank circuit using a voltage divider circuit (see schematic).

I have a few American radios and Heathkit variable valve HT and filament power supply. I use them with an isolated 240-110V stepdown transformer.
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Old 14th Mar 2020, 12:47 pm   #17
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Default Re: Heathkit Q meter movement won't zero

Quote:
Originally Posted by regenfreak View Post
...
It is going to be hard to rebalance the movement as the spring has to be removed and a replacement counterweight has to attached the right position.
...
Hi regenfreak,

You could try rebalancing the movement, you have not much to loose.

The hairspring does not have to be removed!
Do not touch that as it probably will mean the end of the meter!


You need to move those small spiral wire weights that are on those "appendages" next to the pointer to balance the meter. You can move them by warming them up, with the tip of a small, lower than normal temperature soldering iron.

You balance the movement in two steps.
(The balance weight configuration of your meter is like the diagram on the right side of the enclosed picture.)
First keep the meter that the pointer is vertical, pointing upward, then turn the movement 180 degrees that the pointer is downward.
When it is balanced the pointer should point to he same position relative to the frame of the movement.
Adjust the weight on the side, adjusting one of them is enough. Do check it again, pointing it up and down, adjust till you are satisfied.
You should adjust to an error of balance better than the accuracy class of the meter, that is 1.5% or 2%, that is usually marked on the face-plate of the movement.

The second step is to turn the movement that the pointer is horizontal. Than turn the movement 180 degrees that pointer points to the other way. When in balance, the pointer should stay in the same position relative to the frame of the movement. Adjust the counterweight opposite to the pointer.
Do not touch the counterweights on the side, the ones you adjusted before, they do not have any effect on the balance in this position of the meter. Those counterweights do not apply any moment on the pointer/coil assembly in this orientation of the meter movement.
Adjust the counterweight till you are satisfied with the balance.

Adjusting the balance of the meter in this two steps, the effect of the counterweights on the sides and opposite to the pointer are decoupled from each other.

I hope I did not make it too confusing!

If you can, experiment with a broken, not needed meter! You would need a steady hand for sure!
As for a low temperature, small soldering iron, you could twist a couple of turns of 1mm or so dia copper wire around your "regular" soldering iron and use the tip of that wire to heat the counterweights. Again, do experiment before you ruin your meter movement.
(Do not ask how do I know it;-)

Regards, Peter
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Old 14th Mar 2020, 2:59 pm   #18
regenfreak
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Default Re: Heathkit Q meter movement won't zero

Dear Peter
Many thanks for suggestions. This is the most informative explanation about movement balancing online. I have looked at a few websites, they all give vague descriptions about movement balancing.

I have sketched the steps described by you (attached photo). I think I understand the idea of cross-coupling between the horizontal and vertical C.G.s (Center of Gravity; there are horizontal C.G. and vertical C.G. of the whole pivoted assembly). If the horizontal CG and vertical CG coincide with the pivot point, there is zero coupling so the movement is invariant of the orientation of the movement.

Your suggested steps only works if the balance weight is not missing. I think not all the balancing weights are bilateral for the side "appendages",the example below has a discrete lump of metal and unilateral wire on one side only:

https://www.petervis.com/avo-meters/...nt-repair.html

I have two temperature control solder stations (with hot air desoldering and also powered vaccum pump desoldering) . In addition, I have a few working new cheapo Chinese analogue milliamp meters that are used for valve tube tests and homebrew radios. I don't know if the modern Chinese analogue meters would have the same balance weight configurations. Probably I may pick one as a sacrificial lamb.

This will take more than Dutch courage. I do not have faith with myself and I do not trust my mechanical skill
The Q meter has 50uA FS (Full Scale) deflection on the front plate for a maximum Q of 250 or 500.

In theory, I can find another 50uA microamp meter with the same angular sector angle (I think they are all very similar) and wire it externally to replace the faulty Q meter. I can take a frontal photo of the Heathkit meter non-linear Q scale and transfer it to Photoshop. Then I can correct the parallax or perspective errors with Photoshop CS, re-scale and print a new scale matching the size of the replacement micro amp meter. This is just an idea coming out of my head at the moment. Maybe too much hassle!
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Old 14th Mar 2020, 4:45 pm   #19
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Default Re: Heathkit Q meter movement won't zero

Quote:
Originally Posted by regenfreak View Post
...
Your suggested steps only works if the balance weight is not missing. I think not all the balancing weights are bilateral for the side "appendages",the example below has a discrete lump of metal and unilateral wire on one side only:...
Hi regenfreak,

I think you got the right idea of the method of balancing!

The balancing method works even when there is an adjustable weight on one side only!
They usually use two weights because of the physical constraints.
The wire weight needs to be a couple of turns, and it has to be placed at some distance from the pivot point.
If the coil/pointer assembly is reasonably balanced on its own, without any balancing weights, then one weight would be too much, it has to be counteracted by a similar weight at the other side.
The reason for that meter movement having a counterweight only on on side in your reference, I am guessing that the basic assembly without any counterweight was so "crude", was out of balance by so much that one counterweight was not overcompensating the balance.

Yes, a 50uA meter is quite sensitive, its mechanism quite fragile. Not the best one to learn on!

On the other hand, I found that in Q-meter measurements the indication of a peak is a lot more important than the accurate reading of the Q itself, so the balancing does not need to be perfect.
Looking for another 50uA meter movement as replacement sounds like a reasonable backup plan!

Regards, Peter

Last edited by orbanp1; 14th Mar 2020 at 5:06 pm.
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Old 14th Mar 2020, 7:17 pm   #20
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Default Re: Heathkit Q meter movement won't zero

Peter
Thanks for reply again.

Quote:
On the other hand, I found that in Q-meter measurements the indication of a peak is a lot more important than the accurate reading of the Q itself, so the balancing does not need to be perfect.
Looking for another 50uA meter movement as replacement sounds like a reasonable backup plan!
This is comforting for me. As I am not fussy about the exact Q but a rough value is good enough.

The sector angle of the Heathkit Q meter scale is annoyingly 100 degrees! Out of luck again. I believe the standard scale sector angle is 90 degrees for most analogue meters I got.

50uA analogue meters are widely available and inexpensive both vintage and new. If the Heathkit Q meter scale had 90 degrees sector angle, I could make a scaled photographic reproduction of the original Q-scale matching exactly the replacement meter's front plate. Since I have a high-ended professional camera and a long focal length marco lens that can produce high-resolution, distortion free image of the original Q-mater scale, I can resize the scaled reproduction print to fit the new meter using Photoshop CS.

Quote:
Yes, a 50uA meter is quite sensitive, its mechanism quite fragile. Not the best one to learn on!
I was looking at some ultra sensitive 10uA and 5uA vintage meters on ebay for homebrewing RF passive meter. I think they were either used in W-II fighter planes or for levelling bridge during construction!

Last edited by regenfreak; 14th Mar 2020 at 7:24 pm.
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