Pentax Spotmeter circuit diagram User manual

Iifl, on the flip slde of this letten is a cincuit schematic fon the finst
      Asahi lo Spotmeten cinca -1968.
             I obtainod t}e diagrram by tnaclng the cincuit inside the meteF.
     Took about an horir!    I will e-mail you the  .gif   file  if you rrant.
      You can place  it on'foun website.
         Slrrce mencuql  battenies aFe now unavailable  fon this meter,    I substituted  a
       slfver"olidp  ceff in its place 1 a'892 size silye*ortde eett).  Sllveo Oxlde potential  ls
            | .55 vdc compar.ed to the  | .35 vdc 1m*tury  cetth ao the needle will r.ead about a
      stop.and-a-half high eompared to the oniginal voltage.
      The meter cian now be r.ecalibrated by adfusting Rl to a highen nesistance, but
     problem  is that factor.y potentiometen-Rl   is onty eaOO ohms-, and nuns out of
't     adjustment nange  i wichthe newbattcry wtagil.    lt needs about  -3s00  ohms, so I
      substituted a little  lok  ten-turn pot in its place, and ne-calibnated the meten
      with a gr.ey card and t'hnee othen TTL meters  I have her.e. Glose enough.
        In onden bflt   the mueh-smallen sllver.-oxide eell into the battery compaFtmentr
     one has to fabnlcate an alumlnum adapter about the scrne slze as the o"tglnat
       batteryr  that the new cell llves in. We did  it on a metal  lathe.
           .llrso the meten. has a number  of metal-to-motal  switch c€ntaets  that easlly
      oxldize o.ver time and caus6 the ninding  to either become  erratic  or fail
      completely.
      Theyoxidize from  batteryr outgassing  !  without  guestion, these un.neliable
     mechanleal connections are the r,roak point of the design
     The way that Asahi engineered  the LodHigh  switch, the battery.check needs
     and the battery tab is neally poon.
          ( EsPeclelr!fie battery tab. t goGEclean chat one wlth my poeket knife about once a week ll )
           I rronden how many   l" spotmeters  have been tossed into the dumpstoF due to
       this deficit..-  Other than thatr  it is a manvelously precise instrument,
     and is extromely  useful fon zone-type photognaphy.
      -,.  I bought mlne in 1969 and didntt find much use for  it until this yean
    Now it is the only meten  I use.