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Old 29th Oct 2019, 9:39 pm   #1
Barnmead
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Default Model D (Test meter Type D Ref 10/S 10610)

I am trying to sort out one of these instruments made by SEI. All the voltage multipliers are open circuit as are at least two of the other smaller bobbin resistors.

The basic movement is OK (100 mV 1.44mA 70 ohms as far as I can tell)

The lowest DC voltage range seems to indicate that the movement is shunted to measure voltage at 3 mA. DC current ranges work but read high.

I'm wondering if by any chance somebody might have a schematic ?
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Old 29th Oct 2019, 10:39 pm   #2
Ed_Dinning
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Hi Richard, no schematics I'm afraid, but I may have some suitable hi stab resistors for repairs as well as Constantan resistance wire for shunt bobbins.

When you get the details mail me and I'll see what I can find

Ed
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Old 30th Oct 2019, 9:52 am   #3
M0FYA Andy
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Information on this Test Meter is given in A.P.1186E, but I don't have the relevant chapter, unfortunately.

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Old 30th Oct 2019, 7:03 pm   #4
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Thank you for your offer Ed, but I am some way from establishing what is needed. I imagine the meter should have the same sensitivity as the AVO model i.e. 400 ohms/volt so something is seriously amiss but it is difficult to trace out where all the wires go a schematic would help tremendously. In principle it must be similar to the AVO model.

I will search for A.P.1186E thanks
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Old 2nd Nov 2019, 10:28 am   #5
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

The Type D meters are in AP1186E Volume 1, Section 9 but there is only a general decription with no circuit details.

The pages for the SEI type are attached.

If you need other pages from AP1186E, V1. Section 9, please let me know.

PMM
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Old 2nd Nov 2019, 7:07 pm   #6
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

PMM
Thank you, the model I am working on is an earlier one housed in a wooden case though mechanically it is similar to the second photo, the current and voltage ranges are 150/75 rather than 40/20 etc

I see that I should be assuming sensitivity of 400 and 800 ohms/volt so perhaps one step in the right direction. Not an easy task to trace out the wiring.

The meter is reading high so perhaps apart from O/C resistors I have a S/C somewhere.
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Old 2nd Nov 2019, 9:06 pm   #7
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

I have now read the pages properly and see that the 40/20 figures are for type E meter
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Old 2nd Nov 2019, 9:40 pm   #8
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Barnmead,

Sorry the images I sent you were for the GEC Selectest IV version of the Type 'D' meter, designated D3 in AP 1168E. Yours must be the Salford Electrical Instruments Type D2.

There's still not much more information, but just an image, which is attached.

This simplified diagram of the DC ranges of the AVO version, Model D1, may help. (The circuit values may be the same for all version of Type 'D' but that would have to be verified). You will see that the basic movement of the AVO version is 2.5mA fsd, 20 ohms with swamp corresponding to 50mV fsd. (Sorry the quality is poor - I've temporarily mislaid my original drawing from which this is scanned).

With this information, it can be calculated that there is 2.5mA in the multipliers at fsd on any range and so dividing the difference betwen successive range by 2.5mA gives the resistance value for the mulplier section. For example, the difference between the 1.5 and 0.15V ranges is 1.35V. Dividing 1.35V by 2.5mA gives 540 ohms. For the next step, 15 - 1.5 = 13.5V. 13.5V/2.5mA = 5400 ohms, etc.

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Old 4th Nov 2019, 6:31 pm   #9
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Thank you, yes that's the one. Although the circuit must be similar to your diagram so far I have found that the meter 100 mV 1.44mA 70 ohms is very different, the current shunt string is 2ohms and R6 is 50ohms and the Ohms adjustment pot is 100ohms. The K=1 K=2 seems to alter readings correctly. As a diagram seems non existent I will slowly persevere and see what I can produce.
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Old 4th Nov 2019, 7:32 pm   #10
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

You might find this thread useful from when I restored a Early Selectest.
https://www.vintage-radio.net/forum/...ighlight=meter

Good luck Chris
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Old 4th Nov 2019, 9:08 pm   #11
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Chris
Than you, although yours is a later instrument and the interior arrangement is different the resistance values you have determined should help.
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Old 27th Nov 2019, 6:02 pm   #12
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

Update
It seems this is a less sensitive model than the AVO model D or the Selectest ones that Chris has worked on. I have put a bit more time into it and traced out the heart of the circuit which indicates that that 3mA is required for FSD for K=1 as the current shunt chain is always in circuit. I feel there must be something adrift in the resistors directly in series with the meter. Any ideas please.
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Old 27th Nov 2019, 8:03 pm   #13
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

This puts me in mind of a problem with an ACWEECO Model D which took a while to suss out- the K switch was not making and breaking properly. (Granted that this is not an ACWEECO meter therefore 'K' will be a different assembly)

Probably a red herring but thought i'd mention it.

Dave
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Old 14th Jan 2020, 4:39 pm   #14
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Default Re: Model D (Test meter Type D Ref 10/S 10610)

An update.
First of all thank you all for your comments. Like the AVO model D this meter is protected by a fuse which I assume must be interchangeable so should be 4 ohms. As you might expect the fuse had been replaced with a piece of wire but even with 4 ohm resistor in place the meter read high. Using a length of resistance wire I found that a value of 8.1 ohms gave the correct readings on the 150 mV scale and the k=1/2 produced the expected indications A small bobbin resistor of this value is now wired in place of the fuse and I have made up resistors for the 1.5V and 15V ranges.

For the record I noted the terminal resistance on the three (six) DC ranges which are now working
51.0 50.5
508 508
5.07k 5.08k

I don't envisage going any further with it so it is now back together having been cleaned and sleeping on a shelf.
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