Rega RB300 turntable...
 

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

Rega RB300 turntable...
 

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

Rega RB300 turntable...
 

In article ,
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 ?

Only thing I can think of is a metal film one will be more stable?

--
*Errors have been made. Others will be blamed.

Dave Plowman London SW
To e-mail, change noise into sound.

Rega RB300 turntable...
 

"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/

Rega RB300 turntable...
 

"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

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 ?

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 :)

Rega RB300 turntable...
 

"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

Rega RB300 turntable...
 

"Meat Plow" wrote in message
...
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

Rega RB300 turntable...
 

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


Hi Arfa
Just took the cover off a Rega Planar 3 and the board has 5 components
on it.
1 x .22uf 275v ac cap (220nf)
1 x 10k 5% 1-2 watt parallel (physically) to the cap (bn bk or -gold)
1 x 1M 1% 1/4 watt (br bk bk yell -bn)
1 x 3k3 1% 1/4 watt (or or bk bn -bn)
1 x 120nf 400v dc cap
HTH
DaveD

Rega RB300 turntable...
 

"DaveD" wrote in message
...
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
Hi Arfa
Just took the cover off a Rega Planar 3 and the board has 5 components on
it.
1 x .22uf 275v ac cap (220nf)
1 x 10k 5% 1-2 watt parallel (physically) to the cap (bn bk or -gold)
1 x 1M 1% 1/4 watt (br bk bk yell -bn)
1 x 3k3 1% 1/4 watt (or or bk bn -bn)
1 x 120nf 400v dc cap
HTH
DaveD

Hmmm. Well Dave, I've got to say that that bears no relationship to what's
in this one, at all :-\

It definitely says "Rega Planar 3" at the top front right corner, although
it's hard to see as the letters are just black 'shininess' within the black
satin anodised finish of the cabinet. Underneath, directly under the motor,
is a cover secured by two screws, When this is removed, the motor and a
small PCB are revealed. The PCB has just two components on it - the burnt up
R, which is a large 'film' type, I guess something like about 5mm diameter
and 20mm or so long, and the 0.22u 400v cap, which is one of those green MKT
monobloc types. These two components are mounted 'on the slant' on the
board. The mains comes in, and the neutral is joined immediately to two grey
wires from the motor. The live leaves the board again on a white wire which
goes to the on / off switch at the front top left of the deck. Live returns
to the board on another white, and goes to the motor red lead via the burnt
up resistor. The cap is between the red lead and the remaining blue lead.
Doesn't sound much like the example that you're looking at, eh ?

Mind you, dunno about you, but I find this all the time with 'high-end'
gear. Guts that are nothing like what the the service manuals say they
should be, poorly done mods involving extra components stuck across boards,
bog-standard cheap as chips lasers fitted to CD players costing thousands,
metalwork that fits where it touches, holes drilled in wrong places,
inappropriate screw types and sizes - the list is endless.

I know that these things are often hand-built, which I guess is what
attracts the people with more money than sense to them, but when I look at
some items, I wonder how the companies that made them, and then stuck the
multi-thousand pound price tags on them, sleep at night. I guess I've just
got too much of a conscience ...

Anyways, I think tomorrow that I am going to fit a 5 watt 150 ohm wirewound
that I have to hand, and then bring it up gently on the variac, and see what
happens. I guess it's got two chances ... :-)

Arfa

Rega RB300 turntable...
 

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

Rega RB300 turntable...
 

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

Rega RB300 turntable...
 

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.

Rega RB300 turntable...
 

William Sommerwerck wrote:
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.


It's a while since I looked, and I could be wrong but:
The Rega planar motor is a pair of multi pole two phase synchronous
pancake motors sandwiched together with the poles interleaved.
The resistor and capacitor are there to change the phase (lag or lead?)
of one motor so that the assemlby turns in the right direction when it
is started.
Incidentally mine is a Rega 2 and the resistor burnt out too. A day
after a short friendly 'phone conversation with the company the postman
handed me an envelope containing a new resistor (with a higher power
rating).
--
Roger Thorpe

....Wait a minute, It's stopped raining/
Guys are swimming, guys are sailing.....

Rega RB300 turntable...
 

In article , Roger Thorpe
wrote:
William Sommerwerck wrote:
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.


It's a while since I looked, and I could be wrong but: The Rega planar
motor is a pair of multi pole two phase synchronous pancake motors
sandwiched together with the poles interleaved. The resistor and
capacitor are there to change the phase (lag or lead?) of one motor so
that the assemlby turns in the right direction when it is started.

That chimes with my understanding, based purely on having had to 'fix' a
similar problem with a friend's Rega a few years ago. Haven't commented
previously as I don't know the full details. I just replaced the burnt out
resistor with one rated at a higher power. And have since forgotten the
value.

Must admit I was less than impressed with the circuit at the time. From
this thread it does look like this resistor is prone to burning. Although
perhaps that is made worse by the risk of the motor being stalled or
loaded.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Rega RB300 turntable...
 

Roger Thorpe wrote:

William Sommerwerck wrote:
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.


It's a while since I looked, and I could be wrong but:
The Rega planar motor is a pair of multi pole two phase
synchronous pancake motors sandwiched together with the
poles interleaved.
The resistor and capacitor are there to change the phase
(lag or lead?) of one motor so that the assemlby turns in
the right direction when it is started.
Incidentally mine is a Rega 2 and the resistor burnt out
too. A day after a short friendly 'phone conversation with
the company the postman handed me an envelope containing a
new resistor (with a higher power rating).
--

I read it that the resistor is in series with the whole
motor. How could that introduce a relative phase shift
between the two halves?

I looked at the site someone linked to, at the circuit for a
simple synchronous motor. When a resistor is used to drop
the supply voltage, the value of the recommended cap remains
the same. I didn't mention phase, therefore, not because I
know it's not significant, but that I have no evidence to
suggest that a resistor in series makes any difference.

Motors are something of a black art, AFAIK. Two motors in
parallel sharing a cap and resistor is about as black as art
can get. How can a symmetrical circuit favour one direction?
In what way is the circuit not symmetrical? Are you sure
that direction isn't determined by geometry?

Actually, this isn't a good place to explain such a thing.
If you have a name for the type of motor arrangement, maybe
I could look it up?

Ian

Rega RB300 turntable...
 

"PeterD" wrote in message
...
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!

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. 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.
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

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.

Rega RB300 turntable...
 

"Jim Lesurf" wrote in message
...
In article
, Roger
Thorpe
wrote:
William Sommerwerck wrote:
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.


It's a while since I looked, and I could be wrong but:
The Rega planar
motor is a pair of multi pole two phase synchronous
pancake motors
sandwiched together with the poles interleaved. The
resistor and
capacitor are there to change the phase (lag or lead?) of
one motor so
that the assemlby turns in the right direction when it is
started.

That chimes with my understanding, based purely on having
had to 'fix' a
similar problem with a friend's Rega a few years ago.
Haven't commented
previously as I don't know the full details.

Now, since you have now commented, you *do* have the full
details, presumably?

I just replaced the burnt out
resistor with one rated at a higher power. And have since
forgotten the
value.

Oh...maybe not

Must admit I was less than impressed with the circuit at
the time. From
this thread it does look like this resistor is prone to
burning. Although
perhaps that is made worse by the risk of the motor being
stalled or
loaded.

Perhaps? Certainly, surely?

Is it really likely, do you think, that the manufacturer
would continue to fit an inappropriate resistor for so long?
It's not like resistor power rating is complicated or
arcane. Cost difference can't be that significant, and
there's no shortage of space.

It would be interesting to know how the winding resistance
compares with the impedance of an up-to-speed motor. If the
difference is great enough, it could be that all those
burned-out resistors are a result of stalled motors or
increased drag, or even the fitting of heavy platters. It's
also possible that every burned-out resistor has saved a
motor winding, in which case a higher-rated resistor would
be a liability.

Ian

Rega RB300 turntable...
 

"Ian Iveson" wrote in message
...
Roger Thorpe wrote:

William Sommerwerck wrote:
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.


It's a while since I looked, and I could be wrong but:
The Rega planar motor is a pair of multi pole two phase synchronous
pancake motors sandwiched together with the poles interleaved.
The resistor and capacitor are there to change the phase (lag or lead?)
of one motor so that the assemlby turns in the right direction when it is
started.
Incidentally mine is a Rega 2 and the resistor burnt out too. A day after
a short friendly 'phone conversation with the company the postman handed
me an envelope containing a new resistor (with a higher power rating).
--

I read it that the resistor is in series with the whole motor. How could
that introduce a relative phase shift between the two halves?

I looked at the site someone linked to, at the circuit for a simple
synchronous motor. When a resistor is used to drop the supply voltage, the
value of the recommended cap remains the same. I didn't mention phase,
therefore, not because I know it's not significant, but that I have no
evidence to suggest that a resistor in series makes any difference.

Motors are something of a black art, AFAIK. Two motors in parallel sharing
a cap and resistor is about as black as art can get. How can a symmetrical
circuit favour one direction? In what way is the circuit not symmetrical?
Are you sure that direction isn't determined by geometry?

Actually, this isn't a good place to explain such a thing. If you have a
name for the type of motor arrangement, maybe I could look it up?

Ian



Ian. See my later post regarding the correct value, and how it all performed
when fitted. I think that I'm down the same road as Jim was when he did his
mate's one, and judging by what someone else said about Rega sending them a
shiny new resistor of increased power rating, that would seem to be the
right road, if their answer is also upping the rating from what they
originally designed in. Also, its primary function does seem to be that of a
simple dropper to get the 240v mains supply down to something closer to the
110v rating of the motor. My replacement R resulted in 240v in, 98v out
across the motor. I would say that the 0.22uF cap is there to introduce
phase shift between the two stacked windings, to ensure startup, and as
someone else suggested, correct rotational direction. I'm not sure that
stalling is a big current-draw issue for a synchronous motor like it would
be for AC or DC brushgear types. Anyone actually know ?

Arfa

Rega RB300 turntable...
 

In article , Ian Iveson
wrote:

"Jim Lesurf" wrote in message
...

Must admit I was less than impressed with the circuit at the time.
From this thread it does look like this resistor is prone to burning.
Although perhaps that is made worse by the risk of the motor being
stalled or loaded.

Perhaps? Certainly, surely?

No, I can't say for *sure* since I don't now know the rest of the circuit
details or the motor characteristics, fusing, etc. Lacking details I can
only say "perhaps" in the above.

Is it really likely, do you think, that the manufacturer would continue
to fit an inappropriate resistor for so long? It's not like resistor
power rating is complicated or arcane. Cost difference can't be that
significant, and there's no shortage of space.

Afraid I have no data to base a general value of what is "likely". I can
only note that:

1) I found that the resistor was burned out and seemed to me to be rather
small (hence probably low power rating) and replaced it with a higher rated
one.

2) That others here are commenting in a way that supports this idea.

It would be interesting to know how the winding resistance compares
with the impedance of an up-to-speed motor. If the difference is great
enough, it could be that all those burned-out resistors are a result of
stalled motors or increased drag, or even the fitting of heavy
platters. It's also possible that every burned-out resistor has saved a
motor winding, in which case a higher-rated resistor would be a
liability.

That is possible. All kinds of speculations might sometimes return "true".
:-) However in the case of the resistor I replaced the turntable seems to
have worked fine since. The owner seems quite happy with it some years
later.

However, joining you in speculation, the problem with fitting components
with (relatively) low power ratings is that the component tends to run hot
and this can shorten life or lead to other problems. Given the cost of the
turntable it might be better to use a better design for the PSU. Or even
use a fuse that is user-replacable without a soldering iron. Or ensure that
the system is rated to remain undamaged even with a prolonged stall.

I agree that low power resistors are cheap, though. :-)

Slainte,

Jim

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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.