Rega RB300 turntable...
 

On Wed, 19 May 2010 22:44:37 +0100, "Ian Iveson"
wrote:



I've read this a few times but....perhaps you misunderstood.
I was entertaining the theory that the 120 ohm resistor
drops the difference between 220V (or whatever the motor
hopes for) and UK mains, i.e. 10 or 15V, whatever it was
when the deck was made.

IIRC the setup was that the motor was a 120 volt motor used on a 240
volt mains. Not a 220 volt motor on a 240 volt mains. If the desired
drop is only 12 to 15V then you are correct for the value. But that is
not what I understood.

If that difference has increased by,
say 25% from 12V to 15V, then the change that has been
mentioned, from 120 to 150 ohms, makes sense, roughly.
Everything that Arthur has said seems to fit this theory.
It's simple, too.

Anyway, as I understand it, Arthur's worried because if it's
supposed to be a much higher value, he might do some damage.

I'd agree, given the conditions in my comment above, that a 120 ohm
resistor might in fact do damage.

That's why I homed in on the voltage dropping issue.
Whatever else it might do, a resistor in series will
certainly drop voltage. If the value is much too low, then
it could result in a burnout. This is true whatever its
effect on direction, speed, torque and lots of other stuff I
don't know about but probably everyone else does but didn't
fancy saying so until now.

I wonder if he's tried it yet?

Ian


I thought he had, but I'd have to go see if there is a reply.
Something about using three or four larger resistors in parallel...

Rega RB300 turntable...
 

On Mon, 17 May 2010 09:57:09 +0100, Arfa Daily wrote:

Hi all

Anyone happen to know the value of the resistor in the CR network
connected in the synchronous motor feed ? Looks like brown - red - brown
so 120 ohms, but it's well overheated and discoloured, with a nice burn
mark right around the spiral element, right in the centre. Can't get a
reading from either end to the burn point. Looks at a guess to be rated
about 3 -5 watts. Anybody think of a reason *not* to use a wirewound
rather than the original metal film type ?



IIRC the Rega motor is similar to the early Linn unit. There are 2
windings, 90 degrees out of phase with each other. Ignore the motor
voltage rating, they are usually set to run with something around 80v to
85v across each winding. The capacitor gives the phase shift (about 0.2uF
for 50Hz). The resistor is probably about 3.3k 5-7W.

I've been running a 230v Linn from 110v with no problem apart from a
slower run-up time. It reduces motor vibration. No component changes
needed.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

Rega RB300 turntable...
 

On Mon, 17 May 2010 09:57:09 +0100, Arfa Daily wrote:

Hi all

Anyone happen to know the value of the resistor in the CR network
connected in the synchronous motor feed ? Looks like brown - red - brown
so 120 ohms, but it's well overheated and discoloured, with a nice burn
mark right around the spiral element, right in the centre. Can't get a
reading from either end to the burn point. Looks at a guess to be rated
about 3 -5 watts. Anybody think of a reason *not* to use a wirewound
rather than the original metal film type ?



Ah! A bit more research... The voltage dropper resistor on early P3s was
12k, with a 2.2uF phase shift capacitor. Later P3s used a 2.2uF class X2
capacitor instead of the 12k resistor. As I said before, the winding
voltage works out at about 80v when run on a 230v supply.


--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.