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Old 31st May 2020, 8:34 pm   #21
Trigon.
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

I would interpret the diagram rather differently.

I would say it shows two phase shifting capacitors permanently wired, one in series with each of the lower coils. This allows the simple linking to swap between 'full' and 'half' voltage input, maintaining the same phase shifts in the lower coils for each condition.

The additional 3uF seems to be acting as a mains dropper for the intermediate voltage condition.

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Old 31st May 2020, 9:36 pm   #22
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Hi Trigon, that is an interesting thought, but I don't think it fits. If you look at the photo in my post 3, it shows the original capacitor in position. As found there was one capacitor wired in series with the mains lead which fits the description in the figure, and that cap was placed where one of the pair shown were mounted. I do wonder about those two capacitors shown in the figure. It may be that my motor had been modified, or was always different, to the one shown. Mine had no terminal strip, or provision for links, which difference makes it hard to make sense of the connections. Possibly like the chassis in this radiogram, the deck has a series of alterations - my chassis is the later 'jubilee' type which differs from the original.
If it is the case that the motor I had has been fiddled with and has a less than ideal arrangement, I could try to return it to the two capacitor version, but i'd have to have a better idea of the wiring.
It looks to me that perhaps in the version I have, the pair of capacitors were dispensed with, and one repurposed to go in series with the supply, and the whole job simplified so that the terminal strip and link were not needed. Is it possible that these changes had something to do with the section of the primary failing?
I don't understand why if the 3uF was a dropper, no such dropper capacitor was needed for the lowest voltage option. I must say I find it confusing.

Last edited by greenstar; 31st May 2020 at 9:46 pm.
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Old 1st Jun 2020, 7:00 am   #23
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Trigon, a further thought.
The dropper idea does not make sense to me - if the motor is wired to the primary tap, surely it then would not need a dropper. I could see it may do when connected straight to mains input, but in the figure (post 20) for the higher voltage, is is shown absent.
The idea of phase shifting capacitors does make sense, but the motor works fine without them on eithr tap or mains, so?
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Old 1st Jun 2020, 9:25 am   #24
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

The larger upper pole has two (100-130v) windings on a common core - linked in series for 'hi' voltage and in parallel for 'lo' voltage.

The two lower poles are separated physically but are similarly wired in series for 'hi' voltage and in parallel for 'lo' voltage.

In the intermediate voltage condition the windings are still linked for 100-130v , but the voltage is 130-160 - hence the dropper.

If you examine the 130-160 graphic you will see three wires connected to each mains (M) input terminal, i.e. two as per the top centre graphic plus the input wires.

Single phase inductance motors all require some sort of phase shifting to separate poles to create the rotating field. This phase shift can be achieved in several ways. It can be done magnetically as in a shaded pole motor, or by having different values of resistance and inductance in two windings (as per an electricity meter), or by adding a capacitor in series with one of the windings.

Some phonograph disc motors do not have capacitors (relying on differential inductance) and it may be that your windings are sufficiently different to create a phase shift and hence a rotating field, but the designer wished to optimise the phase shift and added capacitance for smoother running or greater torque.

That phase shift is determined by the combination of capacitance and inductance. With a single capacitor the phase shift would be different when the windings were linked for the lo and hi voltages. By having a capacitor in series with each winding the phase shift remains the same in either condition.

If only hi voltage mode is ever going to be required, note that the capacitors are effectively in series and could be replaced by single capacitor of half the value.

I'm not sure the 20uF you measured is feasible in a capacitor of that size and age? You might like to to test for leakage which can seriously confuse some capacitance meters.

Cheers
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Old 2nd Jun 2020, 8:49 pm   #25
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Thanks Trigon. Things are getting clearer. I will take the motor out again and trace the windings connections and see if I can work out how to connect the two capacitors you describe. Might run more quietly. Slowly, slowly catch the monkey.
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Old 2nd Jun 2020, 9:53 pm   #26
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

"Softly, softly" is reputed to work better
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Old 3rd Jun 2020, 8:50 pm   #27
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

I have again taken the motor out of the case, just as the poor thing thought it would be left alone. I had a careful look at the connections and think I have traced them correctly. It's not especially easy to see as all wires are identical in colouring and size and cross over at the point at the bottom where they pass through the laminations.

It is clear that this motor differs from that in the figure, post 20.
There is no terminal strip. There are no links. There are only two wire emerging from the upper winding, that Trigon refers to as the upper pole, therefore, if there are two windings on it, they seem likely to be permanently wired in series. Or indeed parallel. Whatever, there is no option to change.
The two lower windings are wired in series and were also in series with the capacitor.

This arrangement is clearly different from those on the info leaflet. I surmise that like the chassis the motor went through modifications. This version does not appear to have options for various voltages.

My plan now is to keep but replace the capacitor, which is of unknown value - very unlikely to be 20uF as all agree - possibly 2uF as that seems a similar size, and i doubt in 1934ish there were much larger at this voltage and value. It would appear to be a phase shift capacitor.
I am also thinking I will to be safe need to run the motor at 160. My trial with a variac shows it will run at 78rpm at 160v ac. As 160v does not seem available from the tap, I am wondering if I can use an old mains transformer as an autotransformer and stick it in the case somewhere?
The monkey is still at large.
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Old 4th Jun 2020, 9:59 am   #28
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

As it has now been determined to be a single voltage motor, and one which appears to have been run from a mains transformer tap, I'm inclined to think it's most likely to be a 100-130v motor.

How well does it run at 120v ?

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Old 4th Jun 2020, 11:38 am   #29
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Actually, please ignore that last comment - the bottom two windings being in series tends to conradict that theory.

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Old 4th Jun 2020, 7:02 pm   #30
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

I have a vague recollection that there was a Trader sheet covering these HMV disk motors. Does anyone have an index?

Leon.
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Old 4th Jun 2020, 9:25 pm   #31
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

HKS posted these few years back
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Old 7th Jun 2020, 9:41 am   #32
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

This data was scanned from the 21 page EMI service manual 'Electric Gramophone Motors' July 1939.
There does seem to be variations of the type 24 motor. Hope it may help. John.
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Old 7th Jun 2020, 9:59 am   #33
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

John, that's it! Mine is a Type H. 24H is actually stamped on the frame. So that at least shows I have interpreted the wiring correctly. And it shows the capacitor as 1uF, which is a step forward. But is doesn't give the working voltage!
At the moment I am wondering about trying a capacitor dropper to about 160v.
The only thing is. Looking at the service sheet (which doesn't give the voltage either) it is hard to see how the transformer can work yet not give an output at the tap, marked 'C'. Further examination of the transformer is needed. It's a right pain getting the chassis out and worse getting it back. Having done so twice so far!
AND this all helps, really it does. That last thought suggested looking again at the circuit. I have just looked at the Q286 service sheet and found the info attached. I should of course have looked there first. I didn't as I have the later 'Jubilee' chassis, so have been using that service sheet. However, the Q286 sheet gives this information the later one doesn't! To be clear it specifies connecting the motor to tabs B and C. I have been using A (live in) and C. And the Q286 circuit diagram makes it clearer - not enough windings between A and C to run the motor. I will try reconnecting the motor and see if that works. Oh dear!

Tony
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Last edited by greenstar; 7th Jun 2020 at 10:15 am.
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Old 7th Jun 2020, 5:14 pm   #34
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Ok, to maintain my confusion and attempt clarity.
Motor with 1uf capacitor connected to terminals B and C as above. It runs.
It appears to me that there are possibly two arrangements with these radiograms.Using terminals marked A,B,C. Mains in goes to A, L, B, N. in all cases. Also the motor is always connected to B and C.
i/In the original Q286 and the intermediate versions C is connected to one end of the primary.(second image above).
ii/In the later 'Jubilee' chassis C is connected to a tap on the mains transformer primary. This is one of the taps chosen when setting the mains voltage. (first image above)
I don't know what difference if any this makes.


The only problem now is that the motor runs fast. I am struck by the fact that at 160v, it runs exactly at 78rpm, no monkeys. At 225 it is fast to the point my strobe disc is slightly blurry. Not ridiculously fast, but clearly too fast, and the speed control does not bring it down visibly.
I am tempted before this drives me crazy to simply try to fix this by inserting a capacitor dropper. Any thoughts?
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Old 7th Jun 2020, 6:25 pm   #35
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Quote:
Originally Posted by greenstar View Post
ii/In the later 'Jubilee' chassis C is connected to a tap on the mains transformer primary. This is one of the taps chosen when setting the mains voltage. (first image above)
To be clear, what voltage is that particular mains tap labelled as?

Quote:
the speed control does not bring it down visibly
Is the govenor actually known to be working properly? I've only experience of ones on spring driven motors which seem to maintain constant speed pretty well over a surprisingly wide range of torque as the motor winds down.

Cheers
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Old 7th Jun 2020, 6:46 pm   #36
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

[QUOTE=Trigon.;1257120]
Quote:
Originally Posted by greenstar View Post
ii/In the later 'Jubilee' chassis C is connected to a tap on the mains transformer primary. This is one of the taps chosen when setting the mains voltage. (first image above)
To be clear, what voltage is that particular mains tap labelled as?
Trigon, I don't know, I don't have the Jubilee chassis. Mine seems to be an intermediate.

Quote:
the speed control does not bring it down visibly
Is the govenor actually known to be working properly? I've only experience of ones on spring driven motors which seem to maintain constant speed pretty well over a surprisingly wide range of torque as the motor winds down.

I don't know that either, but it seems too much a coincidence that the motor runs at 78rpm at 160v.
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Old 8th Jun 2020, 2:37 pm   #37
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Default Re: Motor and its capacitor on HMV Q286 radiogram, 1934.

Ok, I can add to this.
I have put in a capacitor dropper. 1.5 uF (1+0.47 in parallel), 50 Ohm surge limiter, 220k bleed resistor). This is in addition to the replacement 1uF phase shift cap.
The motor appears to run very happily and I can adjust to exactly 78rpm. No hum.
I can say, Trigon, that the governor does work and I can easily adjust the speed, now the turntable isn't spinning too fast to see the strobe disc operating. Good to have this for the occasional 80rpm record.
I measured 160v across the motor terminals.
Although I do not understand why, it would seem safe to accept there is a mystery and keep this arrangement.
Thank you for all your help people. Particularly as we found the purpose of the original capacitor, and it's value. Hopefully the information here will also help others in future!
Tony
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