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Old 29th Jun 2020, 1:00 pm   #21
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

Nope too early of a call. Both pivot jewel screws are disintegrated inside.
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Old 30th Jun 2020, 12:51 am   #22
Radio1950
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Default Re: Metrix 310B tube tester Meter replacement

That's a brave attempt at a new screw!
Aldous Huxley would be proud.

Great photo of the movement.


Provided that the rest of that original M310 meter is OK, and that there are no iron filings in the magnetic pole area, I think the meter is salvageable.

If you run out of ideas, and you are ready to bin it, consider posting the old meter up to me and let me try with my junk collection?
I don't wish to intrude on your skills, but I may have something.
No guarantees.


By the way, don't touch the rest of the M310 Tester just yet.
The mathematics of the theory of operation has grabbed me and I cannot let it go.
I think I have it all solved.
Those original M310 shunt values are actually correct.

Had to be, as Metrix of France was/is a metrology company, making high quality instrumentation gear.
They probably had primary standards in their lab, and real expertise.

In a few days I hope to reveal all!
.

Last edited by Radio1950; 30th Jun 2020 at 1:12 am.
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Old 30th Jun 2020, 11:37 am   #23
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Default Re: Metrix 310B tube tester Meter replacement

Since the tester is working with AC-voltage the tube under test is half-wave rectifying that voltage so only half the current flows in the circuit. This is the same as with any of the AVO VCMs.

The meter branch is specified with a total resistance of 50 Ohm, and with 1 mA flowing it means that 50 mV will drop over the meter and shunts which are in parallell.

With 50mV across the meter and shunts you can see that for the 100 mA range to work out you get 50 mV / (50 Ohm in parallell with 1.01 Ohm) = 50.5 mA, which is just a small portion from 50 mA which is the half-wave rectified current that you would expect.

The same holds true for the other ranges with, including the 100 mA range as above:

100 mA range: 50 mV / (50 Ohm in parallell with 1.01 Ohm) = 50.5 mA
30 mA range: 50 mV / (50 Ohm in parallell with 3.57 Ohm) = 15 mA
10 mA range: 50 mV / (50 Ohm in parallell with 12.5 Ohm) = 5 mA
3 mA range: 50 mV / (50 Ohm in parallell with 100 Ohm) = 1.5 mA

Another way of seeing this is to just divide the 50 mV across the meter/shunts with the shunt resistance and then adding the 1mA flowing through the meter - so for the 30 mA range you would get 50 mV / 3.57 Ohm + 1mA = 14 mA + 1 mA = 15 mA.

To get 50 mA exactly on the 100 mA range you would need a shunt with some 1.02 Ohm, 50 mV / (50 Ohm in parallel with 1.02 Ohm ) = 50 mA, but Metrix might have used 1.01 Ohm as it might compensate for the small heating of the resistor and meter branch.

Half-Wave rectified AC and its relation to Mean DC and RMS DC can bee seen in the included PDF.
Attached Files
File Type: pdf Bull-DMMglossary-E.pdf (76.7 KB, 104 views)
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Old 6th Jul 2020, 10:52 am   #24
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

OK I tried the dpm as per instructions here. The transformer has been replaced before and no filaments winding from 16-117v. Current reading is abnormally lower than what it should get with tubes I have tested, high current pentodes. Think I might use this metrix as a base for a revamped tester to supply up to 500v for anode and screen supplies. Remove existing - 50v max neg grid bias and add up to 150v with dpm readout. Going to get quote from my trafo supplier to see how much a new custom toroid will cost. Also add a new pot and dpm method to calibrate mains.
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Old 6th Jul 2020, 10:36 pm   #25
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Default Re: Metrix 310B tube tester Meter replacement

Hi again

This is proving to being all quite curious.

If you have used a 100R resistor for the DPM, try now removing that resistor, have the high impedance 200 mV DPM directly across the 1.01R shunt, and use the M310 on "100 mA" range with a test valve.

I still have to do some investigation, and will get back with some more info next weekend, after I go home from present travels.

Dekatron's post is very good.
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Old 14th Jul 2020, 6:23 am   #26
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Default Re: Metrix 310B tube tester Meter replacement

Metrix M310B Valve Tester – Shunts for 200 mV DPM.
Short Story for OP.

To use a 200 mV Digital Panel Meter instead of the original Metrix moving coil meter, and to simulate the original meter deflection, use the following shunts.
These shunts are separate to existing shunts, and in line with the anode current wiring, and switchable, with a few difficulties, if desired.

There should be sufficient resolution if a single range of 0-100 units is used (one decimal point).

Chose to add the new shunts in series with the existing shunts, or mount in a suitable manner to enable switching with original switch.

To simulate the original 100 mA range.
For a 200mV High Impedance DPM displaying 0-100 current units (100 mV on DPM) use 2.25 ohms.

To simulate the original 30 mA range with a 20 mA range.
For a 200mV High Impedance DPM displaying 0-19.99 units (200 mV on DPM) use 22.50 ohms. Adjust DPM Decimal Point for “19.99” display.


The DPM in photos is a generic type (Xieli brand) LED DPM Altronics (AUS) cat Q0588. Needs separate +5V DC Supply.
The M310 in photo has a new 6146 tube and setup as per Manual.
Anode Current adjusted for test values with "Pol" (G1 bias)

To make a 2.25 ohm shunt, I suggest 4 x 10 ohm, and 1x 27 ohm, 1% M.O. resistors, all in parallel.
To make a 22.5 ohm shunt, I suggest 3 x 68 ohm resistors in parallel. This is 0.7% high, but OK.


Longer Story follows.
Bigger than Ben Hur.
.
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Old 15th Jul 2020, 5:55 am   #27
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Default Re: Metrix 310B tube tester Meter replacement

Metrix M310B Shunts for 200mV DPM.

Mathematics ... somewhat drawn out.

The 200 mV DPMs “respond” to the mean current of a half wave sine current.

100 mA Range

On M310 “100 mA” Range, and with the needle indicating FSD of 100, the actual mean DC current is a calculated 45 mA, and a measured 44 mA.

Using a 200mV DPM simulating the M310 deflection, and displaying 100 mV, we require a shunt carrying 45 mA and generating 100 mV.

R shunt = 0.1/0.045 = 2.22 ohms.

20 mA simulating the 30 mA Range (or for use on 100 mA Range)

On M310B, the 30 mA Range is actually 13.5 mA mean, when the needle is on FSD of 30 mA.

When the needle indicates 20 mA, the actual mean current is 0.666 of the 13.5 mA FSD, which is 8.99 mA.

Using a 200mV DPM simulating the M310 deflection, and displaying 200 mV, we require a shunt carrying 8.99 mA and generating 200 mV.

R shunt = 0.2/0.00899 = 22.24 ohms.

For feasibility test, I used 2.25 and 22.5 ohms, as these values correlated slightly better, possibly due to some mains wave shape distortion and other small factors.
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Old 15th Jul 2020, 6:01 am   #28
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Default Re: Metrix 310B tube tester Meter replacement

Metrix 310B Tube Tester Meter and Associated Shunts

(Caution - There appears to be at least six types of Metrix 310 Tube Tester).

The following refers to the M310B version only.

This Tube Tester has Anode Current measurement Ranges of 0-3, 0-10, 0-30, 0-100 mA, and the meter scale is marked 0-30 and 0-100 units, and the scale is marked with “mA and “=”.
The latter symbol implies that the meter itself is calibrated on Continuous DC.

The M310B meter shunts, 1.01, 3.57, 12.57, 100 ohms, are correct values for a 1.0 mA 50 ohm meter movement to give ranges of Anode Current of 0-1.5, 0-5, 0-15, 0-50 mA Continuous DC current.

(These shunts are also installed in other Metrix 310 types, and with other meter movement values eg 0-1 mA 50 ohms).

But ..., the M310B has a 0.9 mA 50 ohm meter movement installed, and with the original shunts, this gives FSD values of 1.35, 4.5, 13.5, and 45 mA for Continuous DC current.

The M310 panel moving coil meter has been confirmed as being 0.9 mA coil FSD, and 15.5 ohms coil resistance, padded out with series resistor R10 of 34.5 ohms, (R9 on some M310B ccts) to be 0.9 mA with total resistance of 50 ohms.
Metrix say in the Tech Notes that when replacing a meter, the resistor must also be replaced. It also says that R10 is normally in the range of 40-50 ohms.

This means that with half wave sine DC whose peak current value is the FSD, the meter will deflect to the “mean” or 0.318 of these Continuous DC FSDs giving “FSD indications” of 0.43 mA, 1.43 mA, 4.30 mA, and 14.3 mA respectively.

That is to say, if the M310B “100 mA” range is selected, and the needle deflects to FSD for a specific tube test, then there is an actual mean anode current of 45 mA (measured), a peak anode current of 141 mA (measured), and by calculation, an RMS current of 70.5 mA.

If the G1 bias is adjusted to obtain a peak tube current of 100 mA on a CRO, then the M310 meter needle “indicates” approx “70 mA”, and a VOM measures a mean of 31 mA.

This has been confirmed by bench experiment, monitoring mean DC current with a moving coil type VOM, and monitoring peak current with a CRO across an extra test 100 ohm series resistor inserted in the tube anode circuit.
Slight departures from theoretical values possibly occur due to mains not being a perfect sine wave shape, and also due to measurement uncertainties.


So DC M.C. meters respond, or deflect, according to the mean current of half wave sine currents, not to RMS values.

For a half wave sine current, the mean is 1/Pi times the peak current, provided it is really sine, not a distorted sine. This is 0.318 of the peak current.

For full wave sine DC current, M.C. meters respond to twice this, which is 2/Pi or 0.636 of peak.

Above confirmed by bench experiment with various setups and scenarios.
My two Metrix 477 VOMs, a CX101 200mV DPM, another LED DPM, and two DVMs, all respond to the mean current for half wave sine DC currents.


Again, the M310 panel moving coil meter is confirmed as being 0.9 mA FSD and 15.5 ohms, padded out with series R10 of 34.5 ohms, (R9 on some circuits) to be 0.9 mA with total resistance of 50 ohms.

The M310 meter itself (probably) is factory calibrated for FSD for each range using 50% of “Steady or Continuous” DC, not with half wave sine.

The Metrix shunts are correct values for a 1mA 50 ohm meter (including the value of R9), for 0-1.5 mA, 0-5mA, 0-15mA, 0-50mA Steady DC.

And the meter scales and Tester front panel Range designation is for twice each actual range value, eg 0-3 mA, etc, to 0-100mA.

So for example, the M310 “0-100 mA” range is actually intended to be FSD with 50 mA Continuous DC, and so on.


To reiterate, if the original shunts are used with the 0.9 mA 50 ohm meter, then the actual current ranges with Continuous DC are 0-1.35, 0-4.5, 0-13.5, 0-45 mA.

If you are testing a tube, and you switch the unit to the “0-100mA” Anode Current range, and you have half scale of indicated anode current, ie “50 mA indicated”, the meter needle with half wave sine DC has deflected to 22.5 mA mean (half of 45 mA real FSD).


The question remains as to why Metrix used those same shunt values with two slightly different meters?

Possibly to obtain a better correlation (RMS to DC) of indicated anode currents when using AC??

I can understand that if the cathode emission capability of a tube can supply a required peak current, and thereby it can supply a certain mean current, as read on the panel meter to establish if the tube is “good”.

Both Metrix (and AVO in places) say that using AC voltage on the tube elements during test gives performance results which correlate to those results when using DC.


I can confirm that the tube anode voltages are as indicated on the M310B front panel are in fact RMS voltages, ie 250 V measures 250V RMS full wave AC.


In any case, the M310B meter indication has to correlate with tube data as listed in their Tube Setup and Performance Manual.

Over to the experts now if required please, as I do not have the requisite experience in Tube Testers.

All above is somewhat mired in detail, but hopefully is correct, and of value to someone.
.
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Old 15th Jul 2020, 6:07 am   #29
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Default Re: Metrix 310B tube tester Meter replacement

Metrix 310B Tube Tester Manuals

For completeness, attached are some manuals and info, with some re-scanned, and some gleaned from other sources.

The Manual of Tube Pin Setups is available ex web, notably eDebris (BAMA) and Kevin Chant sites.

The Test Performance data and Pin Setup seems to be the same in the Metrix M310 and AVO (1965 edn) Manuals.

There also are two different versions of Metrix Tube Pin Setups and Data that I have seen.
.
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Old 19th Jul 2020, 12:33 pm   #30
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

Thanks for the further testing and reply Radio.

With the original analog meter and its missing pivot jewel screw holder I think I have a way to fix this. It will be a long cat and mouse game if I decide to buy every cheap panel meter on ebay AU to try and match the screw. I have a box of assorted lengthed M3-M6 allen head grub screws which I think may do the job. The internal ends of these have cut out conical sections which almost resembles to that of the original found to be securing the pivot jewels of panel meters. Maybe slightly wider in diameter but it may work. Only downside is I'll have to carefully re-tap the top contact bar to suit an M3 grub screw. The hairspring adjuster holder screw will also have to be replaced with something to accommodate the new thread, but this is easy and any replacement should suffice. The important thing is proper contact with the screw and the pivot jewel so its also free flowing and doesn't cause pivot sticking/friction and also not too loose where the needle/coil/pivot will fall out of place.

I've etch primed the base housing today as the previous finish is dull and rusted. I think the problem with the low readings with the DPM may due to dirty and contaminated rotary switch contacts between the wafers and/or the octal socket as well (only tested high current octal tubes on my inital DPM changeover).

Will experiment a bit more and may have another 310B coming my way, one that looks to have not been molested or had parts replaced inside. If this 310B doesn't work out, I'll replace the El core transformer with new winding supply for anode/screen up to 500v at 120mA (to compensate for the loss in the circuit) to not trigger the existing cut out circuit relay.
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Old 27th Jul 2020, 9:21 am   #31
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Default Re: Metrix 310B tube tester Meter replacement

Hi again

Well, you are brave, and adventurous beyond my aspirations!

At least the top pivot screw doesnt have to be an exact fit, it just has to work.
FIY Jaycar has a set of tiny size taps and dies.

And, if you are just after a useable tester, as distinct from a saleable unit, you can still always retreat to the DPM, or a replacement meter ex Altronics inter alia.
If you ever go down this latter path, I can make up a new meter scale for the asking.

You probably have a few watchers in the wings on this subject, so please let us know how you get on.

Good luck, with this, and ... "other things".
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Old 17th Aug 2020, 2:04 am   #32
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

Ok, I haven't had anymore time to work on the existing unit, but I did have another unit shipped to me from France. Issue is known with the meter but that is fine, all electronics and filament windings is intact on this unit compared to the one I had which seem to have had past repairs or molested by somebody who thought they were too clever for the repair.

The new 310 meter looks to have some work done on it before, very minor but there are signs of an attempt to re-glue the glass with some sort of super glue (anybody who has worked with glass and glues know that hard setting glue such as super glue disintegrates over time especially with bonding between X material and glass). The two rubber ring seals are present which is good (I've cleaned these up and soaked them in hot water for approx 40 mins to let it rejuvenate itself a bit as it was hard and brittle).

Now to the actual meter movement, the needle shows erratic movement, sticks at particular points. Based off my experience this is due to debris that has settled in between the walls of the coil, the center iron or the walls of the magnet. Opened it up carefully and lo behold I was right. Lots of tiny metal debris stuck in between the gap preventing full smooth movement of the coil.

Spent an hour using teflon tipped tweezers with sticky paper and bluetak carefully cleaning the coil gap and wall of the magnet. Rebalanced to zero and oddly enough the 900uA is around the 47mA mark on the scale. Testing it via a HP benchmeter on 1mA current shunted through a 10k resistor as it was all I had on hand. My methodology may be wrong. Will try again tonight.

Housing of the unit was cleaned, wiped down and wax polished. The replacement metal handle had a dull finish, polished it with a cotton wheel and Mothers Mag metal and aluminium polish compound, installed pair of wider washers behind the handle to try close off the gap (original black handle was wider).

All chicken head pots removed and cleaned. and top panel wiped. Will need to investigate the current modifications with the shunt resistors for the 3 ranges. Overall underside is clean, no oxidization or grime on the rotary pot contact fingers (unlike my other unit).

Last edited by Matthew kane; 17th Aug 2020 at 2:10 am.
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Old 20th Aug 2020, 8:31 pm   #33
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Default Re: Metrix 310B tube tester Meter replacement

G'day

How does one disassemble the meter please?
I am trying to visualise the rubber sealing rings.
Would you have any photos of the disassembly process, or the inside of the meter?

I dont understand the 47 mA reading.

And I have sometimes wondered just how many years it takes for the magnet in a PMMC meter movement to lose say 5 % of its magnetic effect.
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Old 21st Sep 2020, 6:52 am   #34
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Default Re: Metrix 310B tube tester Meter replacement

So some pictures of the meter pivot screw replaced and repaired.
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Old 21st Sep 2020, 7:00 am   #35
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Default Re: Metrix 310B tube tester Meter replacement

Few more pictures.

Very time consumer repair and replacement job.
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Old 21st Sep 2020, 11:16 pm   #36
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

Seems like I'am not having any luck with these old sort of meters, they seem to lose magnetism therefore meter sensitivity increases and loss of magnetic dampening.

The meter I repaired above, FSD values follows:

Repaired meter:
65.3-65.5 ohms
Approx 1.4mA

With the internal magnetic shunt completely turned clockwise, the sensitivity drops down to about 1.3mA

Meter 2 from ebay 310B after cleanup of stray particles inside the coil gap causing meter sticking
21.5 ohms
Approx 2300uA

Just ordered 2 of the Altronics 0-30V Q0535 MU52E panel meters.
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Old 26th Sep 2020, 6:56 am   #37
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Default Re: Metrix 310B tube tester Meter replacement

Metrix M310B meter scales if you need them for the Altronics MU52E analog meters.

The scales are drawn up in the "free to download" French program “Galva” by F5BU.
Takes some time to learn, but it is very good, and configurable to most requirements.

Scale in PDF for M310B is attached, as well as the source Galva Dat file.
The Galva dat file is disguised as a .doc file so as to load here.
Rename the file extension from .doc to .dat
If you print from “Galva” the print is exact size, plus minus 0.5mm or so.
You may have to experiment a little to print the PDF to required size.
Print on matte photo paper.
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File Type: pdf Metrix 310B MU52E vsn 2.pdf (55.1 KB, 71 views)
File Type: doc Galva M310B MU52E vsn 2.doc (2.5 KB, 59 views)
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Old 7th Oct 2020, 3:22 am   #38
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

I ended up making new scales in Meter by Tonnesoft.
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Old 7th Oct 2020, 5:30 am   #39
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Default Re: Metrix 310B tube tester Meter replacement

If i understand properly, you have a spare meter for a Metrix U61 tester and that is mechanically a perfect replacement for the dead meter in your 310B tester. And its scale is OK as well.

Its FSD is wrong and its series resistance is wrong to go with the switched resistors for the other current ranges.

With a single opamp you can make this simulate any FSD current and series resistance you wish. The meter needs to float with up to 450v AC on it, so the opamp and its power supplies would need to do so too.

This means making a dual power supply with a small transformer. The transformer primary to secondary insulation would need to be good for not only the mains voltage, but also an extra 450V AC. Not the end of the world.

For good opamps, you could even get away with this dual supply being unregulated.

You could try the idea out quickly with a floating pair of batteries to power the opamp to be sure you're happy with the result before tackling the floating power supply.

This is a common way around substituting for a dead meter in an AVO VCM.

Lastly, not only will the scaling of a digital panel meter be wrong for handling half-wave rectified AC instead of DC, it is likely that the A to D converter in the DPM is a dual-slope integrating type, and it will not work properly with fluctuating current. Likely the integrating time is chosen to null mains frequency components so results will be very uncertain given frequency discrepancy between the clock of the ADC and your local mains. I'd expect the reading to wander cyclically at a beat frequency. You'd have to filter the voltage to the DPM to give it unwavering DC.

Sorry for chucking in yet more problems.

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Old 11th Oct 2020, 7:42 am   #40
Matthew kane
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Default Re: Metrix 310B tube tester Meter replacement

90% done.

4 more tube testers go after this.
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