speed inaccuracy Garrard 401

[sreten]

The variation you observe implies the slip speed is reducing and this implies the load on the motor is reducing.

Must have had my logic hat on back to front yesterday.

The observation is the amount of slip speed is increasing
slightly, slowing the turntable slightly, this could imply the
load is increasing slightly.

But that doesn't make any sense, you'd expect
things to loosen up if anything after half an hour.

Possibly the motor is heating up and drawing less current ?
Which requires a slightly higher slip speed for the load ?

sreten.

 

[PeterW]

Possibly the motor is heating up and drawing less current ?
Which requires a slightly higher slip speed for the load ?

sreten,

Indeed, the motor gets very hot! The problem has been demistyfied if you are sure that the current drawn by the motor will decrease by increasing temperature.

I could imagine that the slip must be reduced to counterbalance the decrease in torque caused by a decrease of the current drawn by the motor.

regards,
PeterW

 

[sreten]

sreten,

Indeed, the motor gets very hot! The problem has been demistyfied if you are sure that the current drawn by the motor will decrease by increasing temperature.

I could imagine that the slip must be reduced to counterbalance the decrease in torque caused by a decrease of the current drawn by the motor.

regards,
PeterW

Well the resistance of wire certainly increases as it get hot.

(Note if you define the slip speed as the % it lags the driving
frequency, how fast its going in the opposite direction to
the driving rotation frequency, slip and slip speed increase)

What a pitty that despite its musical capabilities Garrard applied this motor-type in such a wonderful machine like the 401.

TBH i can't really see the logic. Its necessary for the fine speed
control and very minor slow variations over the period of an hour
or so should have no sonic consequence.

sreten.

 

[PeterW]

(Note if you define the slip speed as the % it lags the driving frequency, how fast its going in the opposite direction to
the driving rotation frequency, slip and slip speed increase)

sreten,

I dont' think we talk about different things there, it's just how to define 'slip'. IMO it is the relative difference in synchronous stator speed and asynchronous rotor speed.

If the current in the stator phase decreases, the torque of the rotating magnetic field will also decrease. As a result the slip will increase if the mechanical load doesn't change. To reduce the slip, in other words to increase rotor speed, the mechanical load could be reduced using the eddy-current speed adjuster. The adjustment knob in front of the deck will retract the magnet from the aluminium disc fitted to the motor axis.

regards,
PeterW

 

[sreten]

.

I could imagine that the slip must be reduced to counterbalance the decrease in torque caused by a decrease of the current drawn by the motor.

So the slip must be increased to counterbalance the decrease in
torque caused by a decrease of the current drawn by the motor.

sreten.

 

[johnlennon]

Greetings from India!
I have a Gerrard Turntable; I am not able to see what model no. it is
Now after 35 years of faithful operation, it has started to run slowly. There are no speed variations ; it is just simply roatating at about 15% slower that normal
I couldn't figure out what power supply circuit is being used because the turntable is part of a huge GEC record player with amplifier system. All I could do, is that motor is running on 230V AC (this is the normal wall outlet supply in India)

Could anybody please suggest how I should go about trying to repair this --- build a power supply , get a rewinding done of the coils of the motor ?

Any help would be greatly appreciated as I want to repair this turntable before my Grandfather's 80th birthday as a gift

Thanks and Regards
Arjun

 

[dnsey]

Could anybody please suggest how I should go about trying to repair this

It almost certainly just needs stripping, cleaning and relubricating.
The grease in particular gets very sticky after a while and needs replacing. Despite being 'permanently lubricated', the sintered bronze motor bearings will benefit from cleaning and soaking in light oil for a few hours.