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 ?

Arfa

Arfa Daily wrote in message
...
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 ?

Arfa



Wasn't Rega tonearms only?
What sort of vintage is the deck? Is it definitely for use on 240V mains ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm

"N_Cook" writes:

Wasn't Rega tonearms only?

No, but the RB300 is indeed a tonearm, rather than a turntable. There
are PDF manuals on vinylengine.com for a bunch of Rega tonearms and
turntables which might help identify what the deck actually is.

It's worth noting that the discussion on the page for the Planar 3
(which would be a plausible turntable to have an RB300 fitted) has some
comments on replacement motor resistor values, with one comment
suggesting 150 ohm 5%:
http://www.vinylengine.com/library/rega/planar-3.shtml

--
Adam Sampson http://offog.org/

"Adam Sampson" wrote in message
...
"N_Cook" writes:

Wasn't Rega tonearms only?

No, but the RB300 is indeed a tonearm, rather than a turntable. There
are PDF manuals on vinylengine.com for a bunch of Rega tonearms and
turntables which might help identify what the deck actually is.

It's worth noting that the discussion on the page for the Planar 3
(which would be a plausible turntable to have an RB300 fitted) has some
comments on replacement motor resistor values, with one comment
suggesting 150 ohm 5%:
http://www.vinylengine.com/library/rega/planar-3.shtml

--
Adam Sampson http://offog.org/

Thanks Adam. It is indeed a Planar 3. I had in fact already been on that
site, and seen the reference to the 150 ohm resistor. I suppose it's
possible that there might be more than one value having been fitted over the
life of production, because given 40 odd years of looking at burnt and
discoloured resistor stripes, I definitely would not have said that the
middle one was originally green, but who knows ? (well, hopefully someone on
one of these groups does ! ) I was pretty sure that the first two were
brown and red for 1- 2 - something. I was just concerned that if the final
band was red, or even orange, I didn't want to be putting 120 ohms in there
....

Arfa

Arfa Daily wrote:

Thanks Adam. It is indeed a Planar 3. I had in fact
already been on that site, and seen the reference to the
150 ohm resistor. I suppose it's possible that there might
be more than one value having been fitted over the life of
production, because given 40 odd years of looking at burnt
and discoloured resistor stripes, I definitely would not
have said that the middle one was originally green, but
who knows ? (well, hopefully someone on one of these
groups does ! ) I was pretty sure that the first two were
brown and red for 1- 2 - something. I was just concerned
that if the final band was red, or even orange, I didn't
want to be putting 120 ohms in there ...

What's the resistor for? Assuming the motor draws tens of mA
when running normally, the resistor would need to be a few k
if its purpose is to drop from 240 to 120V.

If it is to drop from UK mains to 220V, then 120 or 150 ohms
would be the right order of magnitude. If an increase in
value is advisable, then that should reflect a proportional
increase in the difference between 220 and UK mains, so an
increase from 120 to 150 ohms would be reasonable.

It's common for motor drivers to use fuse resistors to save
the motor from burning out if it stalls or jams. It could be
that, in your case, the choice of resistor power rating
suitable for protecting the motor is such that the resistor
runs habitually hot, and fails occasionally. I guess a
higher power rating, in combination with a higher
temperature coefficient, might protect the motor equally
well, whilst not burning out so quick under normal
conditions.

Ian

On Wed, 19 May 2010 12:33:27 +0100, "Ian Iveson"
wrote:

Arfa Daily wrote:

Thanks Adam. It is indeed a Planar 3. I had in fact
already been on that site, and seen the reference to the
150 ohm resistor. I suppose it's possible that there might
be more than one value having been fitted over the life of
production, because given 40 odd years of looking at burnt
and discoloured resistor stripes, I definitely would not
have said that the middle one was originally green, but
who knows ? (well, hopefully someone on one of these
groups does ! ) I was pretty sure that the first two were
brown and red for 1- 2 - something. I was just concerned
that if the final band was red, or even orange, I didn't
want to be putting 120 ohms in there ...

What's the resistor for? Assuming the motor draws tens of mA
when running normally, the resistor would need to be a few k
if its purpose is to drop from 240 to 120V.

If it is to drop from UK mains to 220V, then 120 or 150 ohms
would be the right order of magnitude.

Well the turntable draws about 4 watts according the the OP (or
someone else in this thread). So that's 30 MA. To drop 120 volts (240
to 120)at that current and power you would have to use a resistor of
4K. But since half that power is the motor, and half is the resistor,
twice the value (8K) is more appropriate. 120 ohms would result in a
current draw at 120 volts of hundreds of watts!

If an increase in
value is advisable, then that should reflect a proportional
increase in the difference between 220 and UK mains, so an
increase from 120 to 150 ohms would be reasonable.

It's common for motor drivers to use fuse resistors to save
the motor from burning out if it stalls or jams. It could be
that, in your case, the choice of resistor power rating
suitable for protecting the motor is such that the resistor
runs habitually hot, and fails occasionally. I guess a
higher power rating, in combination with a higher
temperature coefficient, might protect the motor equally
well, whilst not burning out so quick under normal
conditions.

Ian

Many turntables have a line resistor. It "does something" (that I don't
understand) to improve speed stability. Or torque. Or something. It's not to
reduce the line voltage.

"N_Cook" wrote in message
...
Arfa Daily wrote in message
...
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 ?

Arfa



Wasn't Rega tonearms only?
What sort of vintage is the deck? Is it definitely for use on 240V mains ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm


Well, sort of. I guess that the full deck is probably a Rega Planar 3, but
definitely a Rega-original product. There is a "Grahams HiFi London" tested
sticker on the bottom with a handwritten date of '86 on it. There is a
manufacturer's label on the bottom also saying "rega Made in Britain" and
"Rega Research Ltd"

To the best of my knowledge, it has always been used here in the UK.The
motor is a synchronous type, 4 wire, and marked 110v 50Hz. Two grey wires go
straight to mains neutral. Switched mains live comes back to a small
(original looking) PCB in the motor compartment. It passes through the R in
question to to the motor red wire. There is then a cap, 0.22u 400v
polyester, between the red wire and the blue wire, so I guess that this RC
combination is a phase shift / AC dropper so that the motor is happy at
240v. There is no indication on any of the labels as to the voltage specs,
but the fact that it is a 50Hz synchronous motor single speed deck, and also
that the mains lead is absolutely original and coloured blue and brown,
would suggest that this was built for use in europe on 50Hz mains of at
least 220v ??

Arfa

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 ?

Arfa

Did you try a 120 and see what happens (with some current limiting in
place) With things like this I usually clip in a light fuse in case the
resistor was actually 1200 ohms or more

"Meat Plow" wrote in message
news
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 ?

Arfa

Did you try a 120 and see what happens (with some current limiting in
place) With things like this I usually clip in a light fuse in case the
resistor was actually 1200 ohms or more

If no closer to a definitive answer by tomorrow, Meat, I'll probably go down
that route.

Arfa