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Darren-UK · 9th Nov 2011, 1:32 am

Apart from the obvious difference when compared to mains-only machines, these types differ in one other respect; namely the use of a DC can motor for the deck. Typically, these motors are designed for 9V operation and some may be in plastic housing but often in an alloy can (hence the name).

For some images of the workings of a battery-only record player, including its motor, see this thread concerning a Stella/Philips machine.

These motors often have a hidden secret, a speed governor. On the alloy canned motors, part of the can is designed to be slid off for access to the governor. On other, later, machines with plastic cased motors, governor access varies - if one is fitted. The purpose of the governor is to set the motor speed when the batteries are in good order, maintain the speed and, related to this, to prevent overspeed when batteries are new and thus a volt or so above their nominal rating. As batteries begin to fail the contacts will remain closed and this, to a degree, compensates for a small loss in battery voltage. See the images and their descriptions below for further details.

Battery and mains battery machines may have single-play decks (frequently) or autochanger decks (sometimes). In either case, faults causing slow speed are the same as with mains-only machines - the exception being the motor governor. If you have a problem which you think you've narrowed down to the governor, please create a dedicated thread with the relevant details as governor settings can be fiddly to correct.

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^ This image shows a DC can motor, this particular motor being fitted originally to a BSR GU7 deck. This same motor can also be found installed on a version of the BSR UA15 autochange deck for use in battery/mains-battery machines. Clear in this image are the three mounting points and their grommets, as mentioned earlier in connection with mains-powered motors. Also clear is the stepped drum (pulley), plus the two recessed screws which secure it to the motor shaft. This drum is a complete unit, as opposed to the type also mentioned earlier with which only the 78RPM section is a seperate component.

Click image for larger version

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^ This image shows the same motor with its cover removed (it simply pulls off), thus exposing the speed governor. The governor comprises a set of contact points similar to those found in a telephone dial or in the distributor of a petrol engine prior to the days of electronic ignition. The contacts are opened by centrifugal force, thus the entire governor unit rotates with the motor. The point at which the contacts open is regulated by the screw seen at bottom right. Once the motor begins to overspeed, the contacts open, cut power, close and reapply power. This happens so rapidly that the motor appears to maintain a constant speed, which it effectively does. At top left can be seen the little brass weight, upon which centrifugal force acts in order to open the contacts. The AA cell is there to prop the motor for the camera but also gives a size comparison; this little motor being powerful enough to drive an autochanger as mentioned in the preceding paragraph.

Moving on now, the record players in question are almost all transistorised* and most, but not all, operate from 9V (DC). On mains/battery machines there will be the usual transformer for AC mains input, rectifier (Solid State), smoothing capacitors and, hopefully, anti surge devices. On the battery side you'll find either two or more PP9's, 4½V AD28's** or similar, or a bank or banks of 'D' cells. In fact almost any type of dry cells/batteries can be found but those mentioned are the commonest. Record players were even produced which used no less than four PP9's.

Obviously, mains/battery machines require a means of switching from one power source to another. This may, on later machines anyway, be automatic via the insertion/removal of a detachable mains lead or, more commonly, via a manually operated changeover switch.

Battery arrangements more often than not cater for one battery, or bank of batteries, powering the deck motor with another powering the amplifier. In a few cases, usually later and probably el cheapo machines one battery, or bank of, or two in parallel, will power the whole ensemble.

The two power sources and switching arrangements make fault finding very easy. Causes in italics:

Excessive hum.
This can only be a problem with the mains unit.

Machine works on batteries but not the mains.
No mains input, fault in mains unit, faulty changeover switch and/or associated wiring.

Machine works via the mains but not batteries.
Faulty changeover switch and/or associated wiring, duff batteries, no batteries installed!, faulty/corroded battery connectors and/or associated wiring.

* Valved mains/battery machines did exist but, of the deck, only the pickup was electric, the turntable being spring driven as per wind-up gramophones. These contraptions are, however, outside the remit of this guide.

** The AD28 battery can still be obtained but, as far as is known, nowadays only from online suppliers. It is also rather expensive.

9th Nov 2011, 1:32 am	#13
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Mains/battery and battery-only record players. Apart from the obvious difference when compared to mains-only machines, these types differ in one other respect; namely the use of a DC can motor for the deck. Typically, these motors are designed for 9V operation and some may be in plastic housing but often in an alloy can (hence the name). For some images of the workings of a battery-only record player, including its motor, see this thread concerning a Stella/Philips machine. These motors often have a hidden secret, a speed governor. On the alloy canned motors, part of the can is designed to be slid off for access to the governor. On other, later, machines with plastic cased motors, governor access varies - if one is fitted. The purpose of the governor is to set the motor speed when the batteries are in good order, maintain the speed and, related to this, to prevent overspeed when batteries are new and thus a volt or so above their nominal rating. As batteries begin to fail the contacts will remain closed and this, to a degree, compensates for a small loss in battery voltage. See the images and their descriptions below for further details. Battery and mains battery machines may have single-play decks (frequently) or autochanger decks (sometimes). In either case, faults causing slow speed are the same as with mains-only machines - the exception being the motor governor. If you have a problem which you think you've narrowed down to the governor, please create a dedicated thread with the relevant details as governor settings can be fiddly to correct. ^ This image shows a DC can motor, this particular motor being fitted originally to a BSR GU7 deck. This same motor can also be found installed on a version of the BSR UA15 autochange deck for use in battery/mains-battery machines. Clear in this image are the three mounting points and their grommets, as mentioned earlier in connection with mains-powered motors. Also clear is the stepped drum (pulley), plus the two recessed screws which secure it to the motor shaft. This drum is a complete unit, as opposed to the type also mentioned earlier with which only the 78RPM section is a seperate component. ^ This image shows the same motor with its cover removed (it simply pulls off), thus exposing the speed governor. The governor comprises a set of contact points similar to those found in a telephone dial or in the distributor of a petrol engine prior to the days of electronic ignition. The contacts are opened by centrifugal force, thus the entire governor unit rotates with the motor. The point at which the contacts open is regulated by the screw seen at bottom right. Once the motor begins to overspeed, the contacts open, cut power, close and reapply power. This happens so rapidly that the motor appears to maintain a constant speed, which it effectively does. At top left can be seen the little brass weight, upon which centrifugal force acts in order to open the contacts. The AA cell is there to prop the motor for the camera but also gives a size comparison; this little motor being powerful enough to drive an autochanger as mentioned in the preceding paragraph. Moving on now, the record players in question are almost all transistorised* and most, but not all, operate from 9V (DC). On mains/battery machines there will be the usual transformer for AC mains input, rectifier (Solid State), smoothing capacitors and, hopefully, anti surge devices. On the battery side you'll find either two or more PP9's, 4½V AD28's or similar, or a bank or banks of 'D' cells. In fact almost any type of dry cells/batteries can be found but those mentioned are the commonest. Record players were even produced which used no less than four PP9's. Obviously, mains/battery machines require a means of switching from one power source to another. This may, on later machines anyway, be automatic via the insertion/removal of a detachable mains lead or, more commonly, via a manually operated changeover switch. Battery arrangements more often than not cater for one battery, or bank of batteries, powering the deck motor with another powering the amplifier. In a few cases, usually later and probably el cheapo machines one battery, or bank of, or two in parallel, will power the whole ensemble. The two power sources and switching arrangements make fault finding** very easy. Causes in italics: Excessive hum. This can only be a problem with the mains unit. Machine works on batteries but not the mains. No mains input, fault in mains unit, faulty changeover switch and/or associated wiring. Machine works via the mains but not batteries. Faulty changeover switch and/or associated wiring, duff batteries, no batteries installed!, faulty/corroded battery connectors and/or associated wiring. * Valved mains/battery machines did exist but, of the deck, only the pickup was electric, the turntable being spring driven as per wind-up gramophones. These contraptions are, however, outside the remit of this guide. ** The AD28 battery can still be obtained but, as far as is known, nowadays only from online suppliers. It is also rather expensive.