Devices included in this entry:
ETL GCA10G direct-drive counter (modified 17 pin base)
ETL GSA10G direct-drive selector (modified 27 pin base; pictured in thumbnail)
These strange devices are known as 'direct drive' glow transfer counting tubes: dekatrons specially designed to be coupled to a Nixie display tube without any intermediate hardware. The GSA10G has a series of ten supplemental anodes arranged equidistantly around the inside of the tube, one for each output cathode. Nixie tube cathodes are connected to these anodes, as the glow transfer passes by a supplemental anode the flow of current will jump between it and the primary anode, causing the appropriate character in the Nixie tube to illuminate. The primary anode has a series of fins around it's perimeter, which isolate the glow transfer to specific supplemental anodes during operation.
The GCA10G is an earlier counting-only variant of Ericcson direct drive technology, and lacks many refinements, such as the finned primary anode and curved secondary anodes. (GCA10G's with late date codes seem to adopt these features.) The GCA10G's lack of selector output cuts the pins on the base down to 18, compare this to the GSA10G, which has a monstrous modified 27 pin base with an extra pin in the center of the socket.
Unfortunately the GSA10G and GCA10G were a technology that few actually felt was necessary. Dekatrons already directly indicate their count position, and few felt the substantial additional cost of a Nixie tube was worth it just to give counter operators an Arabic character to stare at. Very few direct drive dekatron part numbers were made and fewer still were used in products. The GSA10G example shown here is actually an Ericsson development sample; the label includes terse warnings about the lack of future supply.
ETL GSA10G Datasheet (PDF)
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