On 13/12/2015 14:43, Adrian Tuddenham wrote:
N_Cook wrote:

3 pics of this disc
http://www.diverse.4mg.com/marguerite1.jpg
http://www.diverse.4mg.com/marguerite2.jpg
http://www.diverse.4mg.com/marguerite3.jpg

Typical centre-start transcription disc of the period. Broadcasters
sometimes used centre-start to make sure the louder climax of a
performance was recorded at the highest surface speed to give best
quality.

Common practice for continuous programmes lasting longer than one disc
side was to use two recording machines (often with a single common
amplifier). Sometimes thesae were set up so that one recorded
outside-in and the other inside-out, this meant that the changeover on
playback was less noticeable because the surface noise didn't suddenly
change its quality. This system was not popular with the playback
operators, who had to check each side carefully and often made mistakes.

The label suggest that there is no question that the intended playing
speed was 50 RPM - but it is definitely non-standard.

To vary the speed without a lot of butchery, connect the turntable motor
through a step-up auto-transformer to the 100v output of a large P.A.
amplifier. Feed the amplifier from an audio signal generator and adjust
the frequency to get the required speed change. Carefully monitor the
motor current and adjust the amplifier gain so that it is maintained at
a similar value to the normal 50c/s current, otherwise you will burn out
the motor at low frequencies.

Alternatively, look out for a secondhand Lenco turntable with infinitely
variable speed.


The tearing around the spindle hole is the only obvious failing of the
film, clumsy positioning over a spindle in antiquity?

No, these discs weren't played many times, so it is more likely to be
caused by shrinkage of the laquer film pulling away at the centre. It
also appears to have delaminated at the rim for the same reason.

Film laid down like silicone slivers and resist etc in chippery
production? spun at high speed with a dot of liquid on the disc?

....or edge dipped into a bath of laquer whilst rotating slowly. Both
techniques were used.

The colours are about right, plum-brown in flat light and coppery tone
with slanting light reflecting off the aluminium. The apparent grooves
on the rear is probably machining marks of the Al blank.

They weren't usually machined, the blanks were stamped out of sheet
aluminium. Without examining this one closely, I wouldn't like to guess
at what caused that.


Perhaps the 50rpm business was a "pirated" manufacturer trying to escape
patent infringement, I suppose patent library is one route to look into.

No chance, hardly anybody but the BBC and GPO could get hold of MSS
blanks during the war; the GPO ran the factory. By 1944 aluminium was
in very short supply, so private recordings, when they could be made at
all, were being made on glass and even galvanised iron blanks (they were
heavy!). The BBC monitoring services recorded onto wax cylinders.

I'll check again , but the blank space between 2 tracks, with
continuation groove, spirals in such a fashion that playing from sinside
to out , the disc would be spinning normal clockwise , so hopefully
normal handedness of the tonearm and normal antiskating weight.

A centre-start disc still rotates in the conventional direction, it is
one of the few conventions in the recording world that never seemed to
be flouted. The only time you would need a reversing turntable is if
you needed to play it backwards to recover a lost turn because of a
jumped groove.



Found a pulley to give +0.5% of 50 RPM, so within normal mains f variation.
I intend to record on minidisc as stereo from a magnetic pickup. At this
stage not playing around with the EQ of the phono amp, any
recommendations for setting the normal domestic amp bass and treble
controls for this first (only?) recording . After a second or 2 at inner
and outer posistions to check antiskating weight and stylus weight is ok