I came across a set of three RCA WV-97A VTVMs that had “Lectrocell” battery eliminators make by Lectrotech.
It's the same size as a D battery.
The Lectrocell was listed in the “Product Report” section of the July 1964 edition of PF Reporter (pages 60-61). I guess that is probably the date the product was first sold.
Eliminate VTVM Battery
The device shown above can be used to permanently replace the dry cell now used in VTVM’s. “Lectrocell” is a miniaturized power supply the same size and shape as the cell it replace: it connects to the AC power input of the VTVM. The unit, from Lectrotech, Inc., is priced at $3.95 and can be installed in a few minutes.
This appears to be the original style of packaging for the “Lectrocell”, based on the PF Reporter product report.
The other two meters had red bottom caps and white encapsulant, rather than black.
This is the newer style of packaging.
Like the modern VTVM battery eliminator circuits, it’s designed for heater circuits where one side is grounded and in common with negative side of the battery for the Ohms function.
I haven’t tried to reverse-engineer the circuit from measurements at the terminals. I don’t think I’ll get to that any time soon.
Does anyone know how to de-encapsulate the epoxy packaging, and have the chemicals and equipment to do it safely? From what I’ve read, I don’t want to go anywhere near trying to dissolve the epoxy on my own.
The Internet Archive has a scan of some Lectrotech product literature. I’ve excerpted the page on the Lectrocell. Click the image for the PDF.
Update
(Mr?) Adams over on the Antique Radio Forum came up with a product notice from the February 1965 issue of Radio Electronics. It contains a schematic that reveals that the Lectrocell is just a half-wave rectifier feeding a 1.5 volt Zener diode shunt regulator. Pity the poor filament transformer driving that load!
