On Tue, 18 Feb 2014, gareth wrote:

"Michael Black" wrote in message
news:alpine.LNX.2.02.1402181359580.14557@darkstar. example.org...
On Tue, 18 Feb 2014, gareth wrote:
There was a time, back inthe 1920s and 1930s, that any active device
(valves in them thar days, tubes for the leftpondians) would cost nearly
a week's wages for the average working man, and so it was good economical
sense to try and use it as many ways as possible simultaneously.
Times have changes, and active devices with performance into the tens
of MegaHertz are now ten-a-penny, so what is achieved by competitions
such as the "Two Transistor Challenge" where it is the costs of switching
(manual, relays) which would be the major outlay?
Not carping, just curious.

There have always been "contests" like that, though sometimes they were
about "build a whole receiver using the same transistor type", or "build a
receiver without any ICs" after ICs had come around.

What I find intriguing is the realisation that valves ("tubes" to you?) can
be operated with only 12V on the anode.

That's not new. There were some articles in the various hobby electronic
magazines in the fifties and sixties about running them at low voltage,
"starved circuits".

Of course, that was about the time when new tubes came along that could be
run off low plate voltage, a sort of last gasp before transistors took
over. You'd see such tubes in car radios in a very specific time span,
tubes for the RF stages, maybe in the IF but those might have been
transistors, and then the audio stage. That period when tubes weren't yet
really good at radio frequencies.

Or the COllins R392, that used 28v plate voltage.

The best "starved circuit" was an article by John W. Campbell (of science
fiction fame) in CQ in the late fifties. It was about running a CRT at
relatively low voltage in an oscilliscope. It drove up sensitivity so you
could do away with amplification for many purposes (and thus the scope was
broadband) but you lost deflection and I think brightness. The scheme
came out of Bell Labs, he mentioned some specially built CRTs for the
purpose that included magnifiers.

Michael