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Bonjour a tous, restoring a 1972 GenRad Sound Level Calibrator 1562-A


Used to calibrate measurement precision mics like Sound level meters like Genrad 1982


The original 9V mercury battery corroded a few parts
TO-5 transistors, 2N1304, 2N1305, housing inside, battery snaps and case parts.

As mercury salts are poisonous,

1/ What is the best solvent to use? 99% iso alcohols seems ineffective.
2/ How hazardous are the mercury compounds used in batteries?
3/ Recommended cleaning procedure?

Seeking a source on the severely corroded TO-5 metal can geranium transistors

2N1305 GERMANIUM PNP 2N1304 GERMANIUM NPN

Many thanks

Jon

Mercury batteries used mercuric (II) oxide. Mercuric oxide is toxic and can
be absorbed through inhalation as well as exposure to bare skin. Not nearly
as bad as dimethymercury (one drop even with a pair of gloves on - it can
get through them) can be lethal. This is from the Chemistry Stackexchange:



Mercury batteries had the advantage of a very flat discharge curve. They
stayed at the cell voltage of 1.35 volts until their end-of-life when the
voltage dropped very quickly. I know photographers have found replacements
for the mercury batteries that were commonly used for powering the light
sensors of film cameras. Some are based on silver oxide cells and others
use alkaline button cells with a voltage converter chip. The housing for
these converts the shape of the button cell into the form factor of the old
mercury cell it replaces. I bought some of these (they are not cheap) for
use in my old Nikon F camera “Photomic” heads. They work fine and no, I
don’t shoot film much any longer; I have used the old Nikon F for testing
out the older Nikon lenses, some of which are supposedly not usable on the
Nikon digital cameras because they require mirror lockup. A friend of mine
successfully uses even these old lenses with the new Nikon Z cameras
because the F to Z mount converter provides enough depth for the backs of
these lenses.

Someone on this list may know of replacements for the larger (I’ve seen
some that are about AA size) mercury cells.

Steve many thanks very long time!

Many thanks for the fast advise! Built 1972..1978 at least.

Found three of my GenRad sound level meters to check it . Must fab a 1.125" to 0.500" aluminum cylinder to adapt the transducer.

1/ ERROR! Battery 9 V CARBON-ZINC not mercury! #1600 1" dia ~ 1.5" Wow, no Hg!

2/ Corrosion most at two Transistors, battery - snap, edge of outer frame, fortunately the Shure transducer seems OK.

3/ Transistors 2N1305,5 corroded but IT STILL WORKS! Seeking replacements TO-5 metal can NPN, PNP Geranium original were Texas Instruments

Will proceed with cleanup and report later.


Bon Journee,
Jon

Rebonjour! Update:

Cleaned a bit, can use a standard 9V alkaline batt with snaps.

Output is IN CAL for freq and 1V at jack.

Needed an adapter, 1.125" to 0.500" reducer to fit my GR mics into the calibrated cavity, they were in the originlas kits but super rare.


I kluged a PVC plastic pipe adapter and used felt gaskets...Voila! ......

With the three 3 GenRad meters, ONE is in CAL at 114 db, the other read a bit low. As all are from 1970s, this is remarkable.

All it needs is some careful corrosion cleaning, new battery snap and replacing the corroded transistors, 2N1304, 2N1305.

For the $25 on ebay I am a happy guy!

Bon journee,

Jon

I have restored one of these. The transistor types are not too critical, you could use just about any old Ge small signal transistors of the right polarity if you can find them. Maybe even silicon. I had to find a substitute for the unobtainable thermistor - now THAT was a challenge!

Morris

Morris many thanks for the note

The transistors are all fine, just corroded can on two.

I cleaned up all the corrosion with isopropyl alcohol and a Dremel buffer. All 6 transistors must be germanium for correct operation. The original lamp and thermistor are intact. Replaced the snap terminal 9V 1" dia x 1.5" original carbon zinc battery with standard E522 alkaline 9V battery, but a tight fit into cylindrical housing.

Bon journée

Jon