[78-L] HMV Junior and Columbia 113a repair work ongoing...

[Inigo Cubillo]

Just to thank everybody for your valuable help for my questions, made last
november, about how could I get parts for reparation of these two machines.

In the end, after following the various clues you gave, I ended working
with George Vollema (Great Lakes Antique Phonograph, MI), Ken Priestley
(Holmfirth Antiques, West Yorkshire, UK), and Meadows & Passmore (Brighton,
UK).

Overall, the repair of the HMV is on its way. It needed a new speed lever
assembly, plus matched springs for the governor. The original governor was
missing the weights and sliding disc, so I fitted them from an old no 34
motor, which happened to fit in the original axis, but I didn't have
matched springs, so it worked but with a disturbing vibration. Ken has
supplied new matched springs, and surplus spring sets slightly larger and
slightly shorter, for me to be able to adjust the speed range properly. Ken
also gave advice for the wood work; the gramophone base was badly warped
and needed straightening. after some weeks submerged in water, it recovered
a flat shape, and now it is drying in the press. George supplied a new
speed lever assembly from an old style Victor IV, which happens to carry
the same motor as the HMV Junior.

For the Columbia, no 15 Viva-Tonal soundbox, George has supplied new fine
rubber gasket tubing, and Meadows & Passmore have supplied a new aluminium
diaphragm. The back rubber joint was also badly rotten, so I made a new one
using rubber joints made for WC water tanks. From two of these, I've cut
out two washers to be glued together (using silicone) to form a back rubber
washer of adequate thickness.

So thanks to all you who provided advice, adresses and contacts to be able
to get the parts.

COLUMBIA 113A TRACKING ADJUSTMENT
Which follows is for curious gramophone tinkers like me. I love making
slight modifications in gramophones for improving their overall
performance. With the Columbia no 15 soundbox from the 113a portable, it is
possible to improve the alignment/tracking problems it has from origin. I
don't know if the US Columbia equivalent model (163) has the same problems,
for the tonearm is slightly different from the british model 113a. The 113a
suffers from bad tracking azimuth, and also bad zenith angle between needle
and record surface. The tonearm and the pivot distance are very short, and
the construction of the tonearm is such that when carrying the needle to
the center of the TT, the needle falls almost on the spindle, with the
diaphragm plane purely radial; there is too small offset, a very small
overhang, and no inwards azimuth tilt at all. This produces a constant
outwards tracking error, small at the inner grooves, but very bad at the
outer grooves of a 12-inch record. Besides that, the built-in soundbox
fixing screw and notch provide a zenith angle of some 45 degrees between
needle and record surface, which is too flat for an orthophonic-like
soundbox. Doctors recommend some 65 degrees instead.

The use of a self-made rubber joint with no screw holes, to be glued to the
neck piece and to the soundbox backplate, provides a chance to adjust the
zenith angle, rotating the soundbox with respect to the neck piece. Thus, a
65 degree angle can be achieved. This is better, especially when using
bamboo needles, as the needle point bisector falls then just vertical on
the record groove, providing better sound, less dragging force, less needle
wear, and less stress on the soundbox, etc.

This zenith adjustment makes the tonearm effective length shorter, for the
needlepoint falls shorter to the tonearm pivot. But instead of aggravating
the azimuth issue, this reduces the inadequate overhang and, for this
geometric design, improves the tracking error in the inner grooves. This is
what can be measured on the actual machine. It can be observed that the
tracking error is small from the middle to the end of a record, where it is
vital to align the needle with the grooves. As a counterpart, the outwards
tracking error at the start of a 12-incher is very bad.

For a better azimuth adjustment, two ways are possible: to use a wedged
rubber washer, and/or a curved neck coupling tube (trunnion) which can be
designed to provide an offset distance and inwards azimuth tilt which
reduce the overall tracking error as desired. I must confess that I've used
a wedged silicone joint in the past for adjusting a better tracking error,
with overall good results. But it caused another collateral problem: due to
the great thickness and softness of the silicone joint, it was too
compliant for a good performance. So now I've stuck to a flat rubber joint,
as in the original design. Still I have to test the curved trunnion for
improving the azimuth. Will report later.

-- 

Inigo Cubillo
Madrid, SPAIN