[78-L] Weak sound WAS Re: Acoustic gramophones sound comparisons, and experiment proposal.

[Inigo Cubillo]

Dave, your credenza weak sound immediately raises a suggestion. Thin sound
may come either from the soundbox or from the sound conduit. Soundbox may
be treated apart, for its correction is a subject on its own. And tests for
the rest of the sound chain may be conducted with the aid of a substitute
of any other brand.
The tonearm must be perfectly airtight. The delicate points are the movable
joints. These must be dismantled, cleaned, and re-greased with a good thick
grease, which ensures ease of movement while helps the joint airtightness.
Dunno if the victor tonearm middle joint is of the threaded type or a plain
sliding tube secured by a screw-in-the-slot, as in some Columbia machines.
The later are more tricky to repair, and if they've been mistreated during
years, and have too much play, are almost impossible to repair properly. If
this type of sliding joint is in good shape, though, a dab of thick grease
applied on the inner tube after thorough cleaning of both parts, before
reassembling, should be enough to re-set it in perfect shape. If it is of
the threaded type, as in HMV machines, after cleaning, light good oil must
be used instead of grease. The long thread secures airtightness, and light
oil is needed to diminish it's friction to a minimum. Grease would make the
joint too heavy, sticky and slow.
Treatment of the base joint of the tonearm is a different matter, for it
usually has several parts, with sliding joints and tube end beds. In
general, when thoroughly cleaned and re-greased in all their sliding
joints, they come to life again. Keep in mind that sliding joints need to
be sealed with grease to make them airtight if they are somewhat worn out
or have too much clearance, which gives an escape of air pressure, and then
of music strength. If they still are in good shape, though, s thinner
grease or oil is needed. This must be examined and worked out with a
mechanical mind, and a certain feeling of how to grease a joint to make it
airtight but frictionless. The ball bearings at the tonearm base can be
cleaned in gasoline or whatever grease solvent without dismantling, if
they're in good shape, and re-oiled. If the balls are full of dirt or dead
grease, maybe dismantling and cleaning of the balls one by one is the way
to proceed. If the balls track has been ever smashed (by accidental kicks
on the tonearm, or forcing of any kind) then the running of the ball
bearing shows jumps, and the horizontal movement of the tonearm is not
soft. The tonearm jerks put undesirable strain on the record grooves. Fat
grease helps to soften the effect, but it is only a bad solution. The track
must be changed or smoothed out. If this is the case, marks of the balls
can be easily seen on the track when examined under a good light. This
repair work may then involve changing the track and maybe the balls too,
and this is very tricky and needs of successive trial and error to adjust
properly.
If the tonearm base has also an upper arm with the typical centering
set-screw, this is also a point of delicate adjustment. But this has
nothing to see with the fable sound.
The tonearm base joint with the horn throat must also be airtight. This can
involve felt washers and the gramophone board in between. All the contact
surfaces must be well cleaned and greased, and the joint well secured with
its strong screws. On HMV machines, the tonearm base is fixed with screws
to the wooden board, and the horn throat is also screwed to the board by
the inner side. Anyway, thick grease will help in making all these joints
airtight.
The horn throat on HMV big machines is a detachable thick metal part, and
is also secured to the horn body by screws and a felt gasket. All this,
cleaned, revitalised with thick grease, and thoroughly screwed back in
position, work wonders with the sound.
Then comes the metal horn (still in HMV reentrant machines, which is the
only big horn I know well). This is made of welded zinc plates. If there
are air escapes at the joints, I don't know how to repair them, but I
imagine that if the whole horn can be immersed in thick good paint, at some
painting shop, so the paint gets into every part of the internal volutes,
the paint when dried would seal any air escapes between the plates.
I've read that early credenzas had a wooden horn mouth, attached to the
larger end of the metal horn. If this is the case, and the wooden part is
easily accessible from the mouth, I would try to seal all the joints and
cracks (if any) by the outer side with a good thick glue, and seal also
inside with a good varnish or shellac. Maybe it would be needed to
revitalise the wood first, with the aid of a suitable creamy or wax-like
product for wood.
If all the joints in the sound tube, from the tonearm end to the horn mouth
are properly treated, cleaned and greased, and all air escapes are sealed,
then the sound of a reentrant machine with any good soundbox and a good
electrical recording, will be astonishingly strong, yet clear and well
balanced. The sound of a Whiteman, Ellington or any other good orchestra
record from late twenties or thirties is warm and full.
So my suggestion is: let the soundbox apart, get another in good shape, one
which has been overhauled and properly adjusted, and work first on the
sound conduit as I've explained. Once you get it as good as possible, then
you can repair the soundbox. I always have several soundboxes at hand for
testing purposes.

Saludos,

Inigo