Very much On Topic: Integrated Vacuum Tubes

[Tony Duell]

> > - What was/is the smallest tube? purpose? 
> 
> RCA's Nuvistor - a family often found in late 1960s TV tuners and some
> test equipments. They are almost always triodes, and are really small -
> 3/4 inch long, maybe 3/8 inch diameter, all metal. RCA made a few half
> sized Nuvistors, but never sold them.

Somewhere I have a valved hearing aid. It's a flat case that fits in your 
pocket containing a 3-stage amplifier. The first 2 stages use DF64s -- 
rectangular cross-section valves perhaps 1/4" wide, 3/16" thick, and 1" 
long, the output stage is a DL64 which is perhaps 1+1/4" long. They have 
5 lead-out wires coming from one end of the device, they could be 
soldered in, but here they're pluged into ting 5-pin sockets (I've seen 
similar xockets with 2 contacts not fitted used a transistor holders). 

There were also cylindrical valves, not much larger, on an 8-wire base.

-tony