Decca 1A - Concealed Weight Adjustment

[Gram1948]

I recently cam across an advert that included the Decca 1A I have. In the advert the point where the tonearm meets the horn was indicated with a note that reads " Improved Tone Arm, perfect articulation, positive clamping and concealed weight adjustment. It's the last bit that has got me beat. What is the "concealed weight adjustment" and how does it work? Up until now when I have played the machine I've simply fully turned the large knurled nut counter clockwise to release the arm and played a record but it appears there is something else going on. Is this an early attempt at tracking weight adjustment?

I've included a few photos...hope someone can throw some light on it.

[Henry]

It certainly is a beautiful machine, in great condition (to judge by the shiny metalwork). How does it sound? I've never seen a bowl-shaped reflective sound board like that one; it's somewhat like a parabolic microphone in reverse. As to the weight adjustment, have you tried various positionings of that blade-like projection opposite the knurled nut?

[Orchorsol]

It certainly is a beautiful machine, in great condition (to judge by the shiny metalwork). How does it sound? I've never seen a bowl-shaped reflective sound board like that one; it's somewhat like a parabolic microphone in reverse. As to the weight adjustment, have you tried various positionings of that blade-like projection opposite the knurled nut?

The blade-like projection engages in the spring clip above, to hold the tonearm up in its retracted position when shutting the lid. I wonder whether the knurled nut adjusts some kind of spring inside the arm tube joint, with the small set screw in the centre holding the joint together?

[Gram1948]

Thanks Henry and Orchosol for your replies. Orchosol is right about the blade. It simply allows the tonearm to clip in an upright position when changing records without the necessity to lock it there with the knurled nut. I'm sure the centre screw in the middle of the knurled nut has a part to play in the weight adjustment particularly as the mechanism is described as "concealed" which leads me to think it's somewhere behind it. Like Orchosol my initial belief was that it simply held the knurled nut in position but maybe it has an adjusting feature. I'm reluctant to fiddle with it until I know more. The knurled nut will lock the arm in any position which in a way could be argued that tracking weight could be adjusted with it but I can't believe that is right in that it would not allow for any vertical fluctuations of the record. Whatever adjustment is made must surely allow for vertical as well as horizontal movement of the arm.

Henry, in answer to your question about how well it plays here is a link to the 1A on You Tube that I did this morning while investigating the "concealed weight adjustment"

https://www.youtube.com/watch?v=6DtuCF9rk7U

Thanks both for your replies

[Gram1948]

Whoops...missed the r out of Orchorsol....sorry!!

[Henry]

Henry, in answer to your question about how well it plays here is a link to the 1A on You Tube that I did this morning while investigating the "concealed weight adjustment"
https://www.youtube.com/watch?v=6DtuCF9rk7U

OK, I must have this machine. In the interest of continuing good international relations, please ship it over at once and I will solve the concealed weight problem and you will never have to worry about it again!

P.S. You may keep the record, I have a few of my own.

[Gram1948]

Hi Henry, I'd love to ship it to you but am somewhat attached to it!!

Orchorsol got me thinking. I've always thought the knurled nut was to lock off the arm in the storage position for transporting but maybe the clip was all that was ever intended to hold it in the bowl. If the knurled nut is for adjustment then it's either inefficient or no longer works as the arm seems to be either locked or free with no degrees in between

[epigramophone]

As a matter of general interest, the latest booklet in the CLPGS Reference Series is "The Decca Portable Gramophone" by Christopher Proudfoot, ISBN978-0-900883-84-2.

It, and many other titles, can be found at www.clpgs.org.uk.

[Edisone]

Found it in the Canadian patent: There's a "spiral spring" under the knurled knob (Figure 7) - its end can be hooked into different holes to adjust its tension. ... I must find my Decca, to see if it's one of these types.

[Gram1948]

Thanks Epigramophone. Yes I have a copy of the CLPGS book. It has the ad in it I have seen but no further explanation.

Thanks also Edisone. I did discover this morning that turning the knurled nut counter clockwise to release the tone arm and then continuing to turn it against the resistance felt when the arm was fully released caused a tension from an inner spring to be felt but I couldn't work out how adjustment was carried out. Your post explains all. Case closed. Many thanks for your help.