I've got an old 21/1 analog spot meter that works great -- except, of course, for the lack of mercury cells to power it. For years I've used zinc-air hearing aid batteries with wads of aluminum foil to get contact with the undersize 375 cells; around 2020 I bought an adapter to use a small lithium button cell regulated to the correct voltage.
Since then, however, I've found two issues: first, the regulator won't pass enough current to operate the dial light (which worked last time I had a good zinc-air in the meter), and second, the lithium cell runs down over about a year even if I'm not using the meter -- presumably because the regulator has some tiny draw even when not supplying any current to the device.
In the past, I've heard of these meters being modified to a) run the dial light from the 9V booster battery, and b) internally regulate current with a switch so nothing draws current from the lithium cell when not in use. Sadly, I'm not electronically savvy enough to make these mods myself, and last time I tried to disassemble my meter to check if the dial light's grain of wheat bulb was still good, I couldn't find the fasteners that hold the case closed.
Is there anyone around who is competent to make these modifications, so my 1960s vintage meter can continue to soldier on toward the century mark (it passed a half century some time ago)? No, technically one of these isn't worth such service, but compared to a modern spotmeter, the conversion probably costs less than buying a new one with similar "look through" operation.
Since then, however, I've found two issues: first, the regulator won't pass enough current to operate the dial light (which worked last time I had a good zinc-air in the meter), and second, the lithium cell runs down over about a year even if I'm not using the meter -- presumably because the regulator has some tiny draw even when not supplying any current to the device.
In the past, I've heard of these meters being modified to a) run the dial light from the 9V booster battery, and b) internally regulate current with a switch so nothing draws current from the lithium cell when not in use. Sadly, I'm not electronically savvy enough to make these mods myself, and last time I tried to disassemble my meter to check if the dial light's grain of wheat bulb was still good, I couldn't find the fasteners that hold the case closed.
Is there anyone around who is competent to make these modifications, so my 1960s vintage meter can continue to soldier on toward the century mark (it passed a half century some time ago)? No, technically one of these isn't worth such service, but compared to a modern spotmeter, the conversion probably costs less than buying a new one with similar "look through" operation.
