JVC Victor Tonearm Counterweight Sag Repair

I acquired my UA7 series tonearm as a piece of a QL10 ensemble, which I bought only to get my hands on the TT101 chassis. After I much modified the QL10 plinth and finally fixed my TT101, I am using it for my Koetsu Urushi.  The very high mass Fidelity Research FR64S with Ortofon LH9000 headshell and B60 base seemed more appropriate for mounting the Koetsu, and I have been very pleased with the results while the UA tonearm sits idle with its counterweight at half mast.  However, by examination, I agree it is a very nicely made tonearm, superior in many ways in terms of quality of construction to some of the high end most costly tonearms we have today. It is well worth repairing.  What do you suppose is its effective mass, assuming a run of the mill headshell of about 10g? Unsubstantiated rumor has it being medium to low mass.

I found an undocumented post about 7045 being effective mass of 14g

(IF add 19% for 7082’s 37mm longer s/p distance/longer tube = 16.7g)

"Re: UA-7045 effective mass

Post by sebar65 » 13 Dec 2021

Hi, I read that the UA 7045 tonearm has an effective mass of 14 g. I don’t succeed to find the source of this information, but I am sure that this tonearm is adapted to any middle compliance cartridge.
Cheers seb."

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VinylEngine and JVC Victor Literature show a very large cartridge/headshell weight range of 12-32g. Victor specifically mentions low mass/high compliance cartridges in their 7045/7082 brochure.

"Specifications

Type: statically balanced arm with new gimbal support for tracing hold system

Length: 350mm

Effective length: 245mm

Overhang: 15mm

Tracking force: 0-3g (0.1g steps)

Cartridge weight: 12-32g (including headshell weight)

Arm elevation range: 40-60mm

Weight: 610g

Accessories: oil damped arm lifter, low capacitance signal cable"

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my collection’s weights

loose cartridges

5.5g: Grado ME+ Mono Cartridge

6g: shure 44e MM; stanton 600 MM; P mount standard (P mount cartridges track at 1.25g)

7g: shure V15 V-P MM, (6g P Mount in a 1/2" adapter weighing 1 gram) (no brush)

8g: AT14Sa MM Shibata on Tapered Aluminum;

8.3g: AT160ML MM, MicroLine on Beryllium

headshells (AA indicates headshell includes azimuth adjustment)

9g: no name lightweight

13g: Victor, came with 7082

headshells with cartridges (AA indicates headshell includes azimuth adjustment)

15g: Sumiko Talisman S, MC Van Den Hul Line Contact on Sapphire Tube;

18g: Shure V15VxMR MM, Jico SAS on Boron 

18g: AT33PTG/II MONO MC in Pat’s AA headshell (rebuilt MicroLinear on Boron by VAS)

18g: AT160ML MM, MicroLine on Beryllium in AT AA Headshell

19g: Shure 97xe MM in Lustre AA Headshell (rebuilt MicroLinear on Boron by VAS)

23g: AT33PTG/II Stereo MC, MicroLinear on tapered Boron

note: two have weights added onto the headshell for use of a light cartridge/headshell combo in a short arm.

 

 

 

from Ortofon: either length 7045 or 7082 is considered MODERATE MASS Arm

There are a few general "rules of thumb" that we need to consider:

* A tonearm whose effective mass is rated at 10 grams or below is considered low mass (e.g. early SME’s, Grace 747 etc.).

A tonearm whose effective mass is rated between 11 and 25 grams is considered moderate mass (e.g. SME 309, IV, IV-Vi, V, Triplanar, Graham).

Arms above 25 grams of mass are high mass in nature (Eminent Technology, Dynavector).

* A phono cartridge whose compliance is rated at 12 x l0ˉ6 or below, is considered low compliance.

A cartridge whose compliance is rated between 13 x l0ˉ6 and 25 x l0ˉ6 is considered high to very high.

Note: Another way of expressing compliance is um/mN. Here a rating of

5 to 10 is considered very low,

10 to 20 is moderate and

above 35 is very high.